Universal Shorts
अम्ल, क्षार एवं लवण — pH, सूचक और रोज़मर्रा के रसायन
Sour, Bitter, and Worth Marks Every Single Cycle
An acid releases H⁺ ions in water. A base releases OH⁻ ions. A base that actually dissolves in water is called an alkali — so every alkali is a base, but not every base is an alkali. That one sentence has decided more statement-based questions than any formula in this chapter.
Why this topic earns its place in your revision: acids, bases and salts show up in SSC, Railway, CTET and BPSC TRE Part II almost every cycle, and the questions are recall-based, not calculation-based. That makes it one of the highest marks-per-hour topics in the whole general science section.
You are really learning three things at once — how to identify an acid or base (indicators), how strong it is (pH), and what forms when the two meet (salts). Every question you will ever see is a variation on one of those three.
अम्ल, क्षार एवं लवण — pH, सूचक और रोज़मर्रा के रसायन
Indicators — The Colour Table Exams Live On
An indicator tells you whether a solution is acidic or basic by changing colour.
Memory hook: phenolphthalein is shy in acid (shows no colour at all) and pink in base. Methyl orange has the opposite temperament — loud red in acid.
Olfactory indicators change smell instead of colour. Onion, vanilla essence and clove oil lose their characteristic smell in a basic solution. Papers ask this directly: "which of the following is an olfactory indicator?"
A universal indicator is a mixture of several indicators, so instead of a yes/no answer it gives a whole colour range and reports the approximate pH.
अम्ल, क्षार एवं लवण — pH, सूचक और रोज़मर्रा के रसायन
The pH Scale — 0 to 14, and the Numbers That Get Asked
pH = −log[H⁺]. The scale runs from 0 to 14: below 7 is acidic, exactly 7 is neutral, above 7 is basic. The small 'p' comes from the German potenz, meaning power, and the scale was introduced by S. P. L. Sørensen in 1909.
Lower pH means more acidic means more H⁺ ions. A change of one pH unit is a tenfold change in acidity — pH 3 is ten times more acidic than pH 4, and a hundred times more acidic than pH 5. This is the single most exploited trap in the topic.
Numbers worth memorising cold:
अम्ल, क्षार एवं लवण — pH, सूचक और रोज़मर्रा के रसायन
Salts — Four Formulas That Repeat Forever
Neutralisation: acid + base → salt + water.
Acid + metal → salt + hydrogen gas (confirmed by the burning-splinter 'pop' test).
Acid + metal carbonate → salt + water + carbon dioxide (turns limewater milky).
The four salts that carry most of the marks:
Common salt, NaCl, is neutral — a strong acid met a strong base and neither one won.
अम्ल, क्षार एवं लवण — pH, सूचक और रोज़मर्रा के रसायन
What Exams Actually Ask
SSC CGL / CHSL / MTS: one-line recall — "which acid is present in tamarind?" (tartaric) or the formula of a named salt. The standard trap is swapping the baking soda and washing soda formulas, because both are sodium salts and look alike at a glance.
Railway NTPC / Group D: everyday chemistry — antacids, the tooth-decay pH, which gas is released when an acid meets a metal. Straight recall, no reasoning.
BPSC TRE-4 Part II (General Studies): an indicator colour question or the pH of a named substance. These papers reuse the litmus and phenolphthalein pairs cycle after cycle.
CTET Paper I and II (Science / EVS): application framing — "a farmer's field is too acidic, what should be added?" The answer is a base: quick lime or slaked lime.
UPSC Prelims: statement-based sets where you judge two or three statements together. Here the tenfold-per-unit rule and the "every alkali is a base, not every base is an alkali" line usually decide the answer.
अम्ल, क्षार एवं लवण — pH, सूचक और रोज़मर्रा के रसायन
Points to Remember
⚠ Exam Tip 1: When a question names a food, answer with the acid, never the salt — curd is lactic, lemon citric, vinegar acetic, tamarind tartaric, spinach oxalic, and an ant sting is methanoic.
⚠ Exam Tip 2: Plaster of Paris must be stored in a moisture-proof container, because damp air sets it. This one line is asked more often than its formula.
आवर्त सारणी — 18 समूह, 7 आवर्त और चार प्रवृत्तियाँ
A Map, Not a List
There are 118 known elements. Nobody memorises 118 sets of properties — you memorise a map, and then read properties off the position.
The map was built in two stages, and papers ask about both.
That one word swap, mass to number, is the single most asked fact in the chapter. It also repaired the anomalies Mendeleev could not explain, such as argon (mass 40) sitting before potassium (mass 39): by atomic number, 18 before 19, the order is obviously right.
Once the map is correct, four trends explain almost everything else.
आवर्त सारणी — 18 समूह, 7 आवर्त और चार प्रवृत्तियाँ
How the Table Is Laid Out
18 vertical groups and 7 horizontal periods.
The groups worth naming, because papers name them:
Period lengths are fixed and get asked directly: period 1 holds 2 elements, periods 2 and 3 hold 8 each, periods 4 and 5 hold 18 each, and periods 6 and 7 hold 32 each.
The lanthanides (atomic numbers 57–71) and actinides (89–103) are pulled out and printed as two rows below the table, purely to keep it a readable width.
आवर्त सारणी — 18 समूह, 7 आवर्त और चार प्रवृत्तियाँ
The Four Trends — Learn Two Directions Only
Every trend question is really asking about one of two movements: left to right across a period, or top to bottom down a group.
1. Atomic radius — decreases across a period (nuclear charge grows while electrons stay in the same shell, so the pull tightens) and increases down a group (a new shell is added each time).
2. Ionisation enthalpy — the energy needed to pull an electron away. Increases across a period, decreases down a group. Noble gases sit at the top of the scale; caesium near the bottom.
3. Electronegativity — the pull an atom exerts on a shared pair. Increases across, decreases down. Fluorine is the most electronegative element, at 4.0 on the Pauling scale.
4. Metallic character — decreases across a period, increases down a group. That is why the left side is metals, the right side non-metals, and a staircase of metalloids (B, Si, Ge, As, Sb, Te) runs between them.
Trends 2 and 3 always move together; trends 1 and 4 always move opposite to them.
आवर्त सारणी — 18 समूह, 7 आवर्त और चार प्रवृत्तियाँ
The Names Before Mendeleev — and the Gaps After
Döbereiner's triads (1817) — groups of three elements where the atomic mass of the middle one was roughly the average of the other two, as in lithium, sodium, potassium. It worked for only a handful of sets.
Newlands' law of octaves (1866) — arranging elements by increasing atomic mass, every eighth element repeated the properties of the first, like notes in a musical scale. It held only up to calcium.
Lothar Meyer independently plotted atomic volume against atomic mass and got the same periodicity as Mendeleev.
Mendeleev's predictions are the part papers love. He left blanks and named the missing elements after the element above them:
The predictions matched so closely that the table was accepted outright.
Hydrogen remains the standing anomaly. With one valence electron it resembles the alkali metals; needing one electron to fill its shell, it resembles the halogens. It is placed in group 1 by convention, not by comfort.
आवर्त सारणी — 18 समूह, 7 आवर्त और चार प्रवृत्तियाँ
What Exams Actually Ask
SSC CGL / CHSL / MTS — direct recall: which law is based on atomic number, who gave the law of octaves, what eka-silicon turned out to be, which element is most electronegative, which group the noble gases occupy. Pure one-liners, and all of them repeat.
Railway NTPC / Group D — the same recall style, with a special fondness for the number of groups and periods, and for the alkali versus alkaline earth distinction.
UPSC Prelims — moves to reasoning: given two elements, which has the higher ionisation enthalpy and why; statement-based items on why atomic radius falls across a period. Learn the reason, not just the direction.
BPSC TRE-4 Part II (General Studies, 40 marks) — the Chemistry subject carries a dedicated Periodic Table chapter, so this is one of the few places where a whole chapter maps to one topic.
CTET and State TETs — classroom-framed items on classification of elements into metals and non-metals.
The standing trap: mixing up Mendeleev with Moseley, and Döbereiner with Newlands. Two pairs, four names — that is where the mark is lost.
आवर्त सारणी — 18 समूह, 7 आवर्त और चार प्रवृत्तियाँ
Points to Remember
⚠ Exam Tip 1: When a question asks which element has the largest atomic radius in a period, the answer is the one on the far left, not the one with the highest atomic mass. Candidates who reason from mass instead of position get this backwards every time.
⚠ Exam Tip 2: 'Most electronegative' is fluorine, but 'most reactive metal' is caesium and 'most reactive non-metal' is fluorine again. Papers put all three in the same set of options and rely on you reading only the last two words of the question.
धातु एवं अधातु — सक्रियता श्रेणी, निष्कर्षण और परीक्षा में पूछे जाने वाले सभी मिश्रधातु
Metals, Non-metals and the Exceptions That Get Tested
The general rules are easy. Metals are lustrous, malleable, ductile, sonorous and good conductors of heat and electricity. Non-metals are dull, brittle and poor conductors. Metal oxides are basic; non-metal oxides are acidic (CO₂ + H₂O → H₂CO₃).
Papers almost never test the rule. They test the exception:
धातु एवं अधातु — सक्रियता श्रेणी, निष्कर्षण और परीक्षा में पूछे जाने वाले सभी मिश्रधातु
The Reactivity Series — One Ladder, Three Predictions
Learn the order once, top (most reactive) to bottom (least):
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au > Pt
Hydrogen sits in the middle as a marker, not as a metal. That single ladder answers three separate question types:
Aqua regia — 3 parts concentrated HCl to 1 part concentrated HNO₃ — dissolves even gold and platinum.
धातु एवं अधातु — सक्रियता श्रेणी, निष्कर्षण और परीक्षा में पूछे जाने वाले सभी मिश्रधातु
Extraction — Position Decides the Method
Top of the series (K, Na, Ca, Mg, Al): so reactive that carbon cannot pull them out. They are obtained by electrolysis of the molten ore or chloride. Aluminium comes from bauxite this way.
Middle (Zn, Fe, Pb, Cu): the ore is first turned into an oxide, then reduced with carbon.
Bottom (Ag, Au, Hg): often found native, or released by simply heating. Cinnabar (HgS) heated in air gives mercury directly.
The thermite reaction: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + a great deal of heat. Aluminium is the reducing agent; the molten iron produced is used to weld cracked railway tracks and machine parts on the spot.
Common ores: bauxite (Al), haematite (Fe), cinnabar (Hg), zinc blende (Zn), galena (Pb), copper pyrites (Cu).
धातु एवं अधातु — सक्रियता श्रेणी, निष्कर्षण और परीक्षा में पूछे जाने वाले सभी मिश्रधातु
Alloys and Corrosion
An alloy is a homogeneous mixture of a metal with another metal or non-metal, made to gain hardness, resist corrosion or lower the melting point. Any alloy containing mercury is an amalgam.
| Alloy | Made of | Used for |
|---|---|---|
| Brass | Copper + Zinc | Utensils, fittings |
| Bronze | Copper + Tin | Statues, medals |
| Solder | Lead + Tin | Joining electrical wires (low melting point) |
| Steel | Iron + Carbon | Construction |
| Stainless steel | Iron + Carbon + Chromium + Nickel | Cutlery, surgical tools |
| Duralumin | Aluminium + Copper + Magnesium + Manganese | Aircraft bodies |
| German silver | Copper + Zinc + Nickel | Ornamental ware — contains no silver |
Corrosion. Iron rusts only when both oxygen and moisture are present; the product is hydrated iron oxide, Fe₂O₃·xH₂O. Silver tarnishes black (Ag₂S) and copper turns green. Prevention: galvanisation (a zinc coat), painting, oiling, electroplating and alloying. Zinc protects even where the coat is scratched, because zinc is above iron in the reactivity series and corrodes first.
धातु एवं अधातु — सक्रियता श्रेणी, निष्कर्षण और परीक्षा में पूछे जाने वाले सभी मिश्रधातु
What Exams Actually Ask
The four traps:
धातु एवं अधातु — सक्रियता श्रेणी, निष्कर्षण और परीक्षा में पूछे जाने वाले सभी मिश्रधातु
Points to Remember
⚠ Exam Tip 1: When a question asks which metal will displace another, do not reason chemically — just check which one sits higher on the ladder. That single check answers displacement, acid-reaction and extraction questions alike.
⚠ Exam Tip 2: If an option says a coating protects iron because it seals out air, prefer the zinc answer instead. Galvanisation works even on a scratched surface, because zinc is more reactive and corrodes in place of the iron — sealing is only part of the story.
परमाणु की संरचना — तीन कण, 2n² नियम और समस्थानिक
Three Particles Decide Every Atom Question
Open any general science paper and you will find one or two atom questions. They are not chemistry so much as bookkeeping — count the particles correctly and the mark is yours.
An atom has exactly three particles worth knowing:
| Particle | Charge | Mass (u) | Found by |
|---|---|---|---|
| Electron | –1 | 1/1840 | J. J. Thomson (1897) |
| Proton | +1 | 1 | E. Goldstein / Rutherford |
| Neutron | 0 | 1 | James Chadwick (1932) |
Protons and neutrons sit packed in the nucleus; electrons circle it in shells. Because the nucleus holds both heavy particles, it carries almost the entire mass of the atom while occupying almost none of its volume.
A neutral atom always has electrons = protons. The moment those two numbers stop matching, you are no longer looking at an atom — you are looking at an ion.
परमाणु की संरचना — तीन कण, 2n² नियम और समस्थानिक
From Plum Pudding to Orbits — Three Models, Three Failures
Thomson (1904) pictured the atom as a positively charged sphere with electrons stuck in it like seeds in a watermelon — the plum pudding model. It explained why atoms are neutral, and nothing else.
Rutherford's gold foil experiment (1911) fired alpha particles at a thin gold sheet. Three observations, three conclusions:
Rutherford therefore proposed a nucleus with electrons revolving around it. But a revolving charged particle must radiate energy and spiral inward, so his atom should collapse in a fraction of a second.
Bohr (1913) fixed exactly that: electrons revolve only in fixed energy shells and radiate nothing while they stay in one.
परमाणु की संरचना — तीन कण, 2n² नियम और समस्थानिक
A = Z + N — The One Formula That Answers Half the Questions
Two numbers describe any atom:
> A = Z + N, so N = A – Z
An element is written as ᴬZX, for example ²³₁₁Na.
Worked example — Sodium (²³₁₁Na):
Z = 11 → 11 protons, and since a neutral atom balances, 11 electrons.
N = A – Z = 23 – 11 = 12 neutrons.
Worked example — Chlorine (³⁵₁₇Cl): 17 protons, 17 electrons, 35 – 17 = 18 neutrons.
Now the ion case, which papers love. In Na⁺ the atom has lost one electron: protons stay 11, electrons drop to 10, neutrons are untouched at 12. In Cl⁻ it has gained one: 17 protons, 18 electrons, 18 neutrons. Charge changes electrons only — never protons, never neutrons.
परमाणु की संरचना — तीन कण, 2n² नियम और समस्थानिक
The 2n² Rule, Valency, and the Isotope Family
Bohr and Bury gave the shell-filling rule:
> Maximum electrons in the nth shell = 2n² → K = 2, L = 8, M = 18, N = 32
Two extra conditions: the outermost shell never holds more than 8, and a new shell only begins after the one before it has at least 8.
Magnesium (Z = 12) → 2, 8, 2. Two electrons outside, so valency 2.
Chlorine (Z = 17) → 2, 8, 7. Needs one more to reach 8, so valency 1.
Now the three look-alike families:
Uses worth memorising: U-235 in reactors, Co-60 in cancer therapy, I-131 for the thyroid, C-14 for dating fossils.
परमाणु की संरचना — तीन कण, 2n² नियम और समस्थानिक
What Exams Actually Ask
SSC CGL and CHSL stay factual: who discovered the neutron, which particle carries no charge, how many neutrons are in a given nuclide. The trap is the discovery pairing — Thomson found the electron, Chadwick the neutron, and swapping them is the commonest wrong option printed.
BPSC TRE-4 General Studies prefers applications: which isotope treats cancer, which one dates fossils, why chlorine's atomic mass is a fraction. It also asks the gold foil conclusions, usually as "most alpha particles passed undeflected, which proves what?"
CTET and state TETs frame the same content around a classroom: a teacher draws two atoms with the same proton count and different mass — what are they called? The answer is still isotopes; the wrapping only looks different.
Railway NTPC and Group D stick to one-liners: charge on a proton, mass of an electron relative to a proton, maximum electrons in the M shell.
UPSC Prelims rarely asks the structure itself but does ask isotope applications inside nuclear-energy questions.
परमाणु की संरचना — तीन कण, 2n² नियम और समस्थानिक
Points to Remember
• Electron — J. J. Thomson, 1897. Proton — Goldstein (canal rays), named by Rutherford. Neutron — James Chadwick, 1932.
• Neutron is the only chargeless particle; electron is the lightest, about 1/1840 of a proton.
• Z = protons = electrons in a neutral atom. A = Z + N, so N = A – Z.
• Gold foil experiment → atom is mostly empty, nucleus is small, dense and positive.
• Rutherford's model failed on stability; Bohr's fixed energy shells rescued it.
• 2n² → K 2, L 8, M 18, N 32. Outermost shell caps at 8.
• Valency = outer electrons, or 8 minus them, whichever is smaller.
• Isotopes same Z; isobars same A; isotones same N.
• U-235 reactors · Co-60 cancer · I-131 thyroid · C-14 carbon dating.
⚠ Exam Tip 1: When an ion appears, change only the electron count. Nine wrong answers out of ten come from someone adjusting the protons too.
⚠ Exam Tip 2: If the question gives you a mass number and asks for neutrons, subtract first and read the options second — one option is always the proton count, sitting there to catch a rushed eye.
पदार्थ की अवस्थाएँ — अवस्था परिवर्तन, वाष्पन बनाम क्वथन और गैस नियम
Three States, One Explanation
Every general-science paper opens somewhere near this chapter, and it looks so easy that most candidates skim it. Then the paper asks which process turns camphor straight into vapour, or why a desert cooler fails in the monsoon, or what the latent heat of fusion of ice is — and the easy chapter has quietly taken three marks.
The whole topic rests on one idea: matter is made of particles, and the state depends on how strongly those particles are held together and how much energy they carry. Heat the particles and they break free; cool them and they lock up again.
Get that single sentence properly, and the definitions, the naming of each change of state, the gas laws and the everyday examples all follow from it. Memorise them as separate lists and you will confuse sublimation with deposition in the hall — which is exactly what the paper is counting on.
पदार्थ की अवस्थाएँ — अवस्था परिवर्तन, वाष्पन बनाम क्वथन और गैस नियम
The Particle Model — What Actually Differs
| Solid | Liquid | Gas | |
|---|---|---|---|
| Shape | Fixed | Takes the container | Takes the container |
| Volume | Fixed | Fixed | Fills the container |
| Force between particles | Strongest | Moderate | Negligible |
| Space between particles | Least | More | Most |
| Compressibility | Almost nil | Very slight | Very high |
| Rate of diffusion | Slowest | Moderate | Fastest |
Two consequences carry most of the questions.
Gases are highly compressible because the particles are far apart — this is why LPG and CNG can be squeezed into a cylinder, and why an oxygen cylinder holds far more gas than its volume suggests.
Diffusion is fastest in gases and slowest in solids, because diffusion needs particles to move past one another. Incense smoke crosses a room in seconds; a copper–gold contact takes years.
Solids do diffuse — just far too slowly to notice.
पदार्थ की अवस्थाएँ — अवस्था परिवर्तन, वाष्पन बनाम क्वथन और गैस नियम
The Six Changes of State — and the Two That Get Confused
Latent heat is the heat a substance absorbs at constant temperature while changing state. The thermometer does not move while ice is melting — all the energy goes into breaking the bonds.
That is why steam at 100 °C burns far worse than water at 100 °C: it carries the extra latent heat and releases it on your skin.
Temperature in kelvin: K = °C + 273. Ice melts at 273 K, water boils at 373 K.
पदार्थ की अवस्थाएँ — अवस्था परिवर्तन, वाष्पन बनाम क्वथन और गैस नियम
Evaporation vs Boiling, and the Gas Laws
Evaporation happens only at the surface, at any temperature, silently. Boiling happens throughout the liquid, at one fixed temperature, with bubbles. Both absorb heat; only one is a bulk phenomenon.
Evaporation speeds up with larger surface area, higher temperature, faster wind and lower humidity. Note the last one: humidity works the other way. A desert cooler is superb in May and useless in a humid monsoon week — the air is already saturated, so nothing more can evaporate.
Evaporation causes cooling, because the escaping particles carry away latent heat. That is why sweating cools you, why water stays cold in an earthen pot, and why acetone feels icy on the skin.
The three gas laws, one line each:
Plasma is the fourth state (stars, neon signs); Bose–Einstein condensate the fifth.
पदार्थ की अवस्थाएँ — अवस्था परिवर्तन, वाष्पन बनाम क्वथन और गैस नियम
What Exams Actually Ask
SSC CGL, CHSL and MTS ask one-line factual items: which substance sublimes, what plasma is, which state has the highest diffusion rate. The recurring trap is sublimation versus deposition — both are direct changes, and the options always contain both.
Railway NTPC and Group D lean on the latent-heat numbers and the steam-burn reasoning, plus kelvin conversion. Candidates lose the conversion mark by subtracting 273 instead of adding it.
BPSC TRE-4 General Science and CTET Paper I / II science frame the same physics through classroom demonstrations — the earthen pot, the wet cloth on a fan, camphor left in a dish overnight. The concept is identical; only the wrapper changes.
UPSC Prelims takes it further into applications: why pressure cookers cook faster (higher pressure raises the boiling point), why water boils below 100 °C on a hill, and why LPG is stored as a liquid under pressure. Expect a reason, not a definition.
पदार्थ की अवस्थाएँ — अवस्था परिवर्तन, वाष्पन बनाम क्वथन और गैस नियम
Points to Remember
⚠ Exam Tip 1: Steam at 100 °C causes a worse burn than water at 100 °C — not because it is hotter, but because it releases 22.6 × 10⁵ J/kg of latent heat as it condenses on the skin.
⚠ Exam Tip 2: Rising humidity slows evaporation. In any "which factor increases the rate of evaporation" question, humidity is the odd one out and is almost always the intended answer to a NOT-type stem.
दैनिक जीवन का रसायन — प्रचलित नाम, सूत्र और उपयोग जो तुरंत याद होने चाहिए
This is the cheapest chapter in general science. There is nothing to derive, nothing to balance and nothing to calculate — you either recall that washing soda is Na₂CO₃·10H₂O or you do not. Yet it appears every single year: two to three questions in SSC CGL and CHSL, one or two in Railway NTPC and Group D, and it sits inside the general science portion of BPSC TRE-4 and CTET as well.
What makes students lose these easy marks is not ignorance, it is confusion between near-twins. Baking soda and washing soda are both sodium carbonates. Plaster of Paris and gypsum are both calcium sulphates. Quick lime and slaked lime differ by one water molecule. Blue and green vitriol differ only by the metal. The paper knows this, and it sets the twin as the distractor almost every time. So learn these in pairs, never alone.
दैनिक जीवन का रसायन — प्रचलित नाम, सूत्र और उपयोग जो तुरंत याद होने चाहिए
The sodium and calcium family carries most of the marks.
Baking soda — sodium bicarbonate, NaHCO₃ — is an antacid and the powder inside soda-acid fire extinguishers. Washing soda — sodium carbonate decahydrate, Na₂CO₃·10H₂O — softens hard water and goes into glass and soap. Caustic soda is NaOH; caustic potash is KOH.
On the calcium side, limestone, chalk and marble are all CaCO₃ — three names, one formula. Heat it and you get quick lime, CaO. Add water to quick lime and you get slaked lime, Ca(OH)₂, which fizzes and gives out heat. Pass chlorine over dry slaked lime and you get bleaching powder, calcium oxychloride, CaOCl₂, used to disinfect drinking water.
And the pair that decides one question a year: gypsum is CaSO₄·2H₂O, but heat it to about 373 K and it becomes Plaster of Paris, CaSO₄·½H₂O — half a water molecule, and that half is the answer.
दैनिक जीवन का रसायन — प्रचलित नाम, सूत्र और उपयोग जो तुरंत याद होने चाहिए
Next, the vitriols and the salts. The word vitriol always means a hydrated sulphate, and only the metal changes:
Blue vitriol (nila thotha) = CuSO₄·5H₂O · Green vitriol = FeSO₄·7H₂O · White vitriol = ZnSO₄·7H₂O · Epsom salt = MgSO₄·7H₂O.
Read them once as a colour-to-metal chain — blue copper, green iron, white zinc — and the distractor stops working.
The other salts worth ten seconds each: common salt is NaCl; nausadar or sal ammoniac is NH₄Cl; hypo, used in photography to fix film, is sodium thiosulphate Na₂S₂O₃; potash alum (phitkari) is a double sulphate used to purify water and to stop bleeding from a shaving cut; Indian saltpetre is KNO₃ and Chile saltpetre is NaNO₃; milk of magnesia, the antacid, is Mg(OH)₂; and vermilion, used as sindoor, is mercuric sulphide HgS.
दैनिक जीवन का रसायन — प्रचलित नाम, सूत्र और उपयोग जो तुरंत याद होने चाहिए
Now the gases, liquids and the acids in your kitchen.
Marsh gas is methane, CH₄ — the main component of biogas and natural gas, and the gas that bubbles out of marshes. Laughing gas is nitrous oxide, N₂O. Dry ice is not ice at all: it is solid carbon dioxide, which sublimes straight to gas without wetting anything.
Vinegar is a 5–8% solution of acetic acid, CH₃COOH. The alcohol in drinks is ethanol, C₂H₅OH. Methanol, CH₃OH, is wood spirit and is poisonous — it causes blindness and death, which is why the two are never interchangeable. Formalin, used to preserve biological specimens, is about 40% formaldehyde in water. Aqua regia is 3 parts concentrated HCl to 1 part concentrated HNO₃, and it dissolves even gold and platinum.
The natural acids: ant sting → formic, curd → lactic, tamarind → tartaric, spinach and tomato → oxalic, apple → malic, lemon → citric.
दैनिक जीवन का रसायन — प्रचलित नाम, सूत्र और उपयोग जो तुरंत याद होने चाहिए
What exams actually ask, and the trap in each.
SSC CGL and CHSL prefer the straight one-liner — "the chemical name of baking soda is…" — but they place the twin as an option. If the question says washing soda and you see both Na₂CO₃ and Na₂CO₃·10H₂O, the decahydrate is the intended answer, because washing soda is defined as the crystalline hydrated form.
Railway NTPC and Group D favour the use, not the formula: which compound disinfects drinking water, which is used in fire extinguishers, which preserves specimens.
BPSC TRE-4 and CTET frame the same fact as a classroom situation — a demonstration where a white powder is heated and gives off a gas that turns lime water milky, which is CaCO₃ releasing CO₂.
The standing trap across all of them is the matching question: four pairs, three correct, one silently swapped — usually hypo, nausadar or caustic potash.
दैनिक जीवन का रसायन — प्रचलित नाम, सूत्र और उपयोग जो तुरंत याद होने चाहिए
Points to Remember
• Baking soda NaHCO₃ · Washing soda Na₂CO₃·10H₂O · Caustic soda NaOH · Caustic potash KOH.
• Limestone = chalk = marble = CaCO₃ → heat → quick lime CaO → add water → slaked lime Ca(OH)₂ → add chlorine → bleaching powder CaOCl₂.
• Gypsum CaSO₄·2H₂O → heat to 373 K → Plaster of Paris CaSO₄·½H₂O.
• Blue vitriol CuSO₄·5H₂O · Green vitriol FeSO₄·7H₂O · White vitriol ZnSO₄·7H₂O · Epsom salt MgSO₄·7H₂O.
• Hypo Na₂S₂O₃ · Nausadar NH₄Cl · Vermilion HgS · Milk of magnesia Mg(OH)₂.
• Marsh gas CH₄ · Laughing gas N₂O · Dry ice solid CO₂ · Aqua regia 3 HCl : 1 HNO₃.
⚠ Exam Tip 1: When two options differ only by water of crystallisation, the one named after a crystal or a wash — washing soda, gypsum, blue vitriol — is the hydrated one. The anhydrous form is almost never the intended answer.
⚠ Exam Tip 2: In matching questions, verify the pair you feel surest about first and strike it out. The examiner swaps only one pair, so eliminating the certain ones leaves the swap standing alone.
क्या हमारे आस-पास के पदार्थ शुद्ध हैं — तत्व, यौगिक, मिश्रण, कोलॉइड और पृथक्करण की हर विधि
Air, sea water, brass and milk are all mixtures. Water, common salt and sugar are all compounds. Copper, oxygen and gold are elements. Almost every question this chapter asks is really asking you to put one substance into one of those three boxes — and then to name the technique that would pull it apart again.
The chapter earns its place in papers precisely because it is pure classification. There is nothing to derive and no formula to remember. Either you know that air is a homogeneous mixture and that brass is one too, or you don't. The separation half is just as mechanical: every technique exploits exactly one property — particle size, density, immiscibility, whether a component sublimes, or a difference in boiling point. Learn which property each technique uses, and you can answer a separation question about a mixture you have never seen in your life.
क्या हमारे आस-पास के पदार्थ शुद्ध हैं — तत्व, यौगिक, मिश्रण, कोलॉइड और पृथक्करण की हर विधि
A pure substance has one kind of particle throughout, and it splits into two families.
An element cannot be broken into anything simpler by a chemical reaction. 118 are named; the first 92, up to uranium, occur naturally. Elements are metals, non-metals, or the seven metalloids — boron, silicon, germanium, arsenic, antimony, tellurium and polonium. At room temperature only two elements are liquid, mercury and bromine, and eleven are gases.
A compound is two or more elements chemically combined in a fixed ratio by mass. Water is always 1:8 hydrogen to oxygen, never 1:7.
The compound–mixture divide is the most-asked idea in the chapter. Iron filings stirred into sulphur powder still look like iron and still answer to a magnet. Heat that mixture and you get iron sulphide — neither magnetic nor yellow. A mixture keeps its components' properties, has no fixed ratio, and comes apart by physical means. A compound loses them, has a fixed ratio, and needs a chemical reaction.
क्या हमारे आस-पास के पदार्थ शुद्ध हैं — तत्व, यौगिक, मिश्रण, कोलॉइड और पृथक्करण की हर विधि
Mixtures are graded by the size of the dispersed particle, and the three names follow straight from it.
In a true solution the particle is smaller than 1 nanometre — invisible, never settles, passes through filter paper, scatters no light. Salt water is a solution; so are air and brass, because a solution need not be liquid.
A suspension carries particles bigger than about 100 nm. They are visible, they settle on standing, and filter paper catches them. Chalk in water and muddy water are suspensions.
Between the two sits the colloid, 1 to 100 nm. It looks as clear as a solution, never settles, passes through filter paper — but it scatters a beam of light. That scattering is the Tyndall effect, the standard test that tells a colloid from a true solution: a sunbeam picked out in a dusty room, or through a forest canopy. Milk is an emulsion, fog and clouds are aerosols, butter and jelly are gels, whipped cream is a foam, coloured glass is a solid sol.
क्या हमारे आस-पास के पदार्थ शुद्ध हैं — तत्व, यौगिक, मिश्रण, कोलॉइड और पृथक्करण की हर विधि
Every technique exploits one property, and naming that property answers the question.
Particle size — filtration for an insoluble solid in a liquid, sieving for grains of different size. Density — sedimentation and decantation for mud in water, winnowing for husk and grain, centrifugation for cream from milk or cells from blood. Immiscibility — a separating funnel for kerosene and water. Magnetism — iron pulled out of a sand mixture.
Sublimation lifts out the one component that goes straight from solid to vapour: camphor, naphthalene or ammonium chloride mixed with salt. Chromatography splits substances that dissolve to different extents in the same solvent, which is how the dyes inside one ink blot come apart.
Evaporation recovers a non-volatile solute. Crystallisation does the same job better — it leaves soluble impurities in the mother liquor and never heats a solid to dryness. Simple distillation separates miscible liquids whose boiling points differ by more than 25 K; below that gap, fractional distillation is required.
क्या हमारे आस-पास के पदार्थ शुद्ध हैं — तत्व, यौगिक, मिश्रण, कोलॉइड और पृथक्करण की हर विधि
SSC CGL and CHSL run the classification question directly — 'Which of the following is a compound?' with air, brass and bronze printed beside water. All three distractors are mixtures, and the item collapses the moment you remember that every alloy is a mixture.
RRB NTPC and Group D prefer the separation half: which technique recovers salt from sea water, which one takes naphthalene out of sand.
BPSC TRE-4 asks the paired definition — the property a colloid shows that a true solution does not, or the particle-size band of each.
CTET frames the same content around a classroom demonstration: a student shines a torch through a glass of milk and through salt water, and you are asked what the difference proves.
UPSC Prelims stays with everyday examples — milk, fog, smoke, butter — each to be matched to the right colloid type.
The trap that repeats everywhere is the boiling-point rule. Papers offer two miscible liquids differing by about 10 K and list simple distillation as an option. The answer is fractional distillation.
क्या हमारे आस-पास के पदार्थ शुद्ध हैं — तत्व, यौगिक, मिश्रण, कोलॉइड और पृथक्करण की हर विधि
Element — one kind of atom; 118 named, first 92 natural. Compound — fixed mass ratio, component properties lost, needs chemistry to split. Mixture — any ratio, properties kept, splits physically.
Particle size: solution below 1 nm · colloid 1–100 nm · suspension above 100 nm.
Tyndall effect — shown by colloids and suspensions, never by a true solution.
Colloid types: milk = emulsion · fog and clouds = aerosol · butter and jelly = gel · whipped cream and shaving foam = foam · paint and milk of magnesia = sol · coloured glass = solid sol.
Only two elements are liquid at room temperature — mercury and bromine.
Alloys — brass, bronze, steel — are mixtures, never compounds.
⚠ Exam Tip 1: When two miscible liquids are given, look only at the boiling-point gap. Above 25 K means simple distillation, below 25 K means fractional distillation. Nothing else in the question changes that.
⚠ Exam Tip 2: Choose crystallisation over evaporation the moment the question mentions purity, or a solid that would decompose on heating — evaporation leaves impurities behind in the residue.
मोल संकल्पना — तीन सूत्र जो ग्राम को उन परमाणुओं में बदल देते हैं जिन्हें गिना नहीं जा सकता
A chemist has a problem no other scientist has quite so sharply: the thing being counted is invisible and the thing being measured is a weight. You can put 11 grams of dry ice on a balance. You cannot put 1.5 × 10²³ molecules on anything.
The mole is the bridge. One mole is simply a fixed count of particles — 6.022 × 10²³ of them, called Avogadro's number — chosen so that the count weighs a convenient number of grams. One mole of carbon-12 atoms weighs exactly 12 grams. One mole of water molecules weighs 18 grams. That correspondence is the whole trick.
Once you accept it, every numerical question in the topic is a conversion between three currencies: grams, particles, and — for gases only — litres. Three formulas move between them, and the next card is all three. Learn which currency the question gives you and which it wants back; the arithmetic is trivial after that.
मोल संकल्पना — तीन सूत्र जो ग्राम को उन परमाणुओं में बदल देते हैं जिन्हें गिना नहीं जा सकता
The three formulas, all of them giving n, the number of moles.
From mass: n = m ÷ M, where m is the given mass in grams and M the molar mass in grams per mole.
From count: n = N ÷ N_A, where N is the number of particles and N_A is 6.022 × 10²³ per mole.
From gas volume: n = V ÷ 22.4, where V is the volume in litres at STP. Gases only.
Work 11 grams of carbon dioxide right through. Molar mass of CO₂ is 12 + 32 = 44 g/mol, so n = 11 ÷ 44 = 0.25 mol. Number of molecules = 0.25 × 6.022 × 10²³ = 1.5055 × 10²³. Volume at STP = 0.25 × 22.4 = 5.6 litres.
One quantity, three answers, no new idea needed. Every question in this topic is that walk, entered at a different door.
मोल संकल्पना — तीन सूत्र जो ग्राम को उन परमाणुओं में बदल देते हैं जिन्हें गिना नहीं जा सकता
Three words get confused in every paper, so separate them once.
Atomic mass is how heavy one atom is compared with one-twelfth of a carbon-12 atom. It is a ratio, so it carries no unit — oxygen is 16, full stop.
Molecular mass adds those up for a molecule. Water is 2 × 1 + 16 = 18. Still a ratio, still no unit.
Molar mass is the mass of one mole of the substance, and it does carry a unit: grams per mole. Its number is the same as the molecular mass. Water is 18 g/mol.
So calculating molar mass is just careful addition. CaCO₃ = 40 (Ca) + 12 (C) + 3 × 16 (O) = 100 g/mol. The error that costs marks here is counting the oxygen once and reporting 68 — the subscript is doing work, and a subscript ignored is a wrong molar mass carried into every later step of the question.
मोल संकल्पना — तीन सूत्र जो ग्राम को उन परमाणुओं में बदल देते हैं जिन्हें गिना नहीं जा सकता
Percentage composition and formulas. Take a compound that is 40 per cent carbon, 6.7 per cent hydrogen and 53.3 per cent oxygen by mass.
Step one, assume 100 grams, so the percentages become grams directly: 40 g C, 6.7 g H, 53.3 g O.
Step two, divide each by its atomic mass to get moles: 40 ÷ 12 = 3.33, 6.7 ÷ 1 = 6.7, 53.3 ÷ 16 = 3.33.
Step three, divide all by the smallest: 1 : 2 : 1. That whole-number ratio is the empirical formula, CH₂O — the simplest ratio of atoms, nothing more.
Step four, if the question also gives a molar mass, divide it by the empirical formula mass. Empirical CH₂O weighs 30; a molar mass of 180 gives 180 ÷ 30 = 6, so multiply every subscript by six: C₆H₁₂O₆, glucose.
Empirical says the ratio. Molecular says the actual molecule. A question that gives you a molar mass is asking for the second.
मोल संकल्पना — तीन सूत्र जो ग्राम को उन परमाणुओं में बदल देते हैं जिन्हें गिना नहीं जा सकता
What exams actually ask. SSC CGL and CHSL general science keep it to one step — the value of Avogadro's number, the 22.4 litre molar volume, or moles from a clean mass like 11 g of CO₂. RRB NTPC and Group D usually stay at definition level: what is a mole, what does Avogadro's number count. BPSC TRE-4 Part II general science asks the molar mass calculation and the mole definition, and a molar mass slip there is expensive because the same wrong figure travels through the rest of the question. CTET and the state TETs frame it as a classroom item — how many particles are in a spoonful of sugar. UPSC prelims touches it indirectly, through parts-per-million in environment questions.
Two traps recur. First, 22.4 litres is for a gas at STP and nothing else; offered for a liquid or a solid it is simply wrong. Second, the number printed in the question is rarely one mole — 9 g of water is half a mole, not one.
मोल संकल्पना — तीन सूत्र जो ग्राम को उन परमाणुओं में बदल देते हैं जिन्हें गिना नहीं जा सकता
Points to Remember. One mole is 6.022 × 10²³ particles, Avogadro's number. Three routes to n: mass ÷ molar mass, particles ÷ 6.022 × 10²³, and gas volume in litres ÷ 22.4 at STP. Molar mass in g/mol is numerically the relative molecular mass; atomic and molecular masses are ratios and carry no unit. CaCO₃ = 40 + 12 + 48 = 100 g/mol. CO₂ is 44, water 18, glucose 180. Empirical formula is the simplest whole-number ratio; molecular formula is the empirical one multiplied by molar mass ÷ empirical mass. CH₂O × 6 = C₆H₁₂O₆.
⚠ Exam Tip 1: 22.4 litres belongs to a gas at STP only. If the substance in the question is a liquid or a solid, any option built on 22.4 is a distractor by construction.
⚠ Exam Tip 2: For 'which sample has the most atoms', count atoms, not molecules. One mole of NH₃ carries four times Avogadro's number of atoms and beats one mole of O₂, which carries only two.
रासायनिक आबंधन — आयनिक, सहसंयोजक, धात्विक, और नमक बिजली क्यों चलाता है पर चीनी नहीं
Atoms bond for one reason: the noble gases are stable and everyone else wants their electron arrangement. Helium is content with 2 electrons in its only shell, and every other noble gas with 8 in its outermost shell. So an atom will give away, take, or share electrons until its outer shell looks like a noble gas. That is the octet rule, with a duplet rule for the tiny atoms — hydrogen, lithium, beryllium — which aim for 2 instead of 8.
How the atom reaches that arrangement decides the type of bond, and the type of bond decides every property the paper then asks about — melting point, solubility, whether it conducts, whether it is hard or soft.
That chain is the whole chapter: electron arrangement → bond type → property. Learn it forwards and you can answer questions backwards, deducing the bond from a list of properties, which is exactly how the harder items are set.
रासायनिक आबंधन — आयनिक, सहसंयोजक, धात्विक, और नमक बिजली क्यों चलाता है पर चीनी नहीं
The ionic bond — transfer. A metal hands electrons over to a non-metal, and the two charged ions that result hold each other by electrostatic attraction.
Work it through with common salt. Sodium is 2,8,1 — one awkward electron in the outer shell. Chlorine is 2,8,7 — one short of eight. Sodium gives its electron away and becomes Na⁺ at 2,8; chlorine takes it and becomes Cl⁻ at 2,8,8. Both now match a noble gas, and the opposite charges lock them into a crystal lattice.
Same logic gives MgO, where magnesium (2,8,2) hands two electrons to oxygen (2,6), and CaCl₂, where calcium's two electrons go to two separate chlorine atoms.
The properties follow from the lattice. Ionic compounds are hard, brittle, crystalline solids with high melting and boiling points, they dissolve in water, and they conduct electricity when molten or dissolved — but not as solids, because the ions cannot move.
रासायनिक आबंधन — आयनिक, सहसंयोजक, धात्विक, और नमक बिजली क्यों चलाता है पर चीनी नहीं
The covalent bond — sharing. Two non-metals, neither willing to surrender electrons, share instead. Each shared pair is one bond.
One shared pair gives a single bond: H₂, Cl₂, HCl, H₂O, NH₃, CH₄. Two shared pairs give a double bond: O₂, CO₂. Three shared pairs give a triple bond: N₂, which is why nitrogen gas is so unreactive — three bonds are hard to break.
Covalent compounds are usually gases, liquids or soft solids with low melting points, they are poor conductors because there are no free ions, and they dissolve in organic solvents rather than in water. Two carbon giants break the pattern: diamond and graphite are covalent yet melt above 3,000 °C, and graphite alone conducts, because each of its carbon atoms bonds to only three neighbours and the fourth electron is free to move.
The coordinate bond is a covalent bond where one atom supplies both shared electrons — as in NH₄⁺ and H₃O⁺.
रासायनिक आबंधन — आयनिक, सहसंयोजक, धात्विक, और नमक बिजली क्यों चलाता है पर चीनी नहीं
Two more attractions complete the picture.
The metallic bond. In a metal, the atoms release their outer electrons into a shared pool and sit as positive cores in a 'sea' of delocalised electrons. Those free electrons explain everything metals do: they conduct heat and electricity in the solid state, unlike ionic solids; they are malleable and ductile, because the layers can slide without breaking the bonding; and they are lustrous.
The hydrogen bond. When hydrogen is attached to a strongly electronegative atom — fluorine, oxygen or nitrogen — it is left slightly positive and attracts a lone pair on a neighbouring molecule. This is a force between molecules, not a true chemical bond, and it is weak individually. Yet it is why water boils at 100 °C instead of somewhere below zero as its molecular mass would suggest, and why ice floats: hydrogen bonds hold the molecules in an open framework that is less dense than liquid water.
As a rough sorter, a large electronegativity difference between two atoms points to an ionic bond, a small one to a covalent bond.
रासायनिक आबंधन — आयनिक, सहसंयोजक, धात्विक, और नमक बिजली क्यों चलाता है पर चीनी नहीं
What exams actually ask.
SSC CGL, CHSL and the Railway papers ask it as one-line property recall, and their favourite item is conduction. Solid sodium chloride does not conduct; molten or dissolved sodium chloride does. Candidates who memorise 'ionic compounds conduct electricity' without the state qualifier lose the mark every time.
The second favourite is the carbon pair. Diamond and graphite are both pure carbon and both covalent, yet graphite conducts and diamond does not, and graphite is soft while diamond is the hardest natural substance. Any question offering both is testing structure, not composition.
UPSC Prelims prefers statement sets on the hydrogen bond — typically one true statement about water's boiling point or the density of ice, paired with a false one calling it a covalent bond.
BPSC TRE-4 keeps bonding inside general science and asks for the bond type in a named compound. CTET and the state TETs frame it as classroom science — sorting everyday substances by whether their solutions conduct.
रासायनिक आबंधन — आयनिक, सहसंयोजक, धात्विक, और नमक बिजली क्यों चलाता है पर चीनी नहीं
Points to Remember
• Octet rule: 8 electrons in the outer shell. Duplet rule: 2, for H, Li and Be.
• Ionic = metal + non-metal, electrons transferred. Covalent = non-metal + non-metal, electrons shared.
• NaCl: Na (2,8,1) → Na⁺ (2,8); Cl (2,8,7) → Cl⁻ (2,8,8).
• Ionic solids: high melting point, water-soluble, conduct only when molten or dissolved.
• Covalent: low melting point, poor conductor, soluble in organic solvents. Exceptions — diamond and graphite.
• Single = 1 shared pair, double = 2, triple = 3. N₂ has a triple bond, hence its low reactivity.
• Coordinate bond: both electrons from one atom — NH₄⁺, H₃O⁺.
• Metallic bond: sea of delocalised electrons — conducts as a solid, malleable, ductile.
• Hydrogen bond: intermolecular, not a true bond. Explains water's boiling point and floating ice.
⚠ Exam Tip 1: On any conduction question, read for the state of matter before you read the compound. 'Sodium chloride conducts electricity' is false as written and true the moment the word 'molten' or 'aqueous' is added.
⚠ Exam Tip 2: Diamond and graphite in the same option list is never a composition question — both are carbon. It is asking about how the atoms are joined, and only graphite has that fourth free electron.
उपचयन-अपचयन, विद्युत अपघटन और सेल — इलेक्ट्रॉन वास्तव में कहाँ जाते हैं
A car battery, a rusting gate, a silver-plated spoon and an aluminium smelter are the same chemistry four times over. In each, electrons leave one substance and arrive at another.
That transfer has two halves and they are inseparable. Oxidation is loss of electrons; reduction is gain. Neither happens alone, which is why the pair is called a redox reaction.
Once you see a reaction as electron traffic, two questions answer everything: who lost electrons, and who took them. The loser has been oxidised and is the reducing agent. The taker has been reduced and is the oxidising agent.
That last sentence is where most marks are won or lost, because it feels backwards. The oxidising agent oxidises something else, and in doing so it is itself reduced. Say it aloud until it stops sounding wrong.
Everything else in this topic — cells, electrolysis, corrosion — is that one idea in different equipment.
उपचयन-अपचयन, विद्युत अपघटन और सेल — इलेक्ट्रॉन वास्तव में कहाँ जाते हैं
Three definitions, widening in scope.
The oldest is about oxygen: oxidation adds oxygen or removes hydrogen; reduction removes oxygen or adds hydrogen. In 2Cu + O₂ → 2CuO, copper is oxidised.
The electronic definition is the one to keep. Oxidation Is Loss, Reduction Is Gain — OIL RIG. In Zn + CuSO₄ → ZnSO₄ + Cu, zinc gives up two electrons and copper ions take them.
The widest is oxidation number: oxidation is an increase in it, reduction a decrease. Rules worth memorising — free element 0, oxygen usually −2, hydrogen usually +1, and the numbers in a neutral compound sum to zero.
Work one: in H₂SO₄, two hydrogens give +2 and four oxygens give −8, so sulphur must be +6. In KMnO₄, potassium +1 and four oxygens −8 leave manganese at +7 — which is why permanganate is such a strong oxidising agent. It has a long way to fall.
उपचयन-अपचयन, विद्युत अपघटन और सेल — इलेक्ट्रॉन वास्तव में कहाँ जाते हैं
Electrolysis is redox forced to happen. An outside source pushes electrons where they would not go on their own.
One rule never changes, in any cell: reduction at the cathode, oxidation at the anode. What does change is the sign. In an electrolytic cell the anode is positive and the cathode negative, because the battery makes them so. Cations travel to the cathode and gain electrons; anions travel to the anode and lose them.
Four uses carry the marks. Electroplating — the object to be coated is the cathode, the coating metal is the anode. Electrorefining of copper — impure copper is the anode, pure copper the cathode, copper sulphate the electrolyte. Extraction of reactive metals — aluminium from alumina dissolved in molten cryolite, sodium from molten sodium chloride. The chlor-alkali process — electrolysis of brine gives chlorine at the anode, hydrogen at the cathode, and sodium hydroxide in solution.
Faraday's first law fixes the quantity: mass deposited is proportional to the charge passed, so m ∝ It.
उपचयन-अपचयन, विद्युत अपघटन और सेल — इलेक्ट्रॉन वास्तव में कहाँ जाते हैं
A galvanic cell is the reverse trade: a spontaneous redox reaction made to deliver current. Here the anode is negative and the cathode positive — the opposite of electrolysis, though reduction still happens at the cathode.
In the Daniell cell a zinc rod in zinc sulphate is joined to a copper rod in copper sulphate by a salt bridge. Zinc is above copper in the reactivity series, so zinc dissolves, releasing electrons that travel through the wire to the copper. The zinc electrode wears away; the copper electrode gains mass.
The cells you use are variations. A dry cell has a zinc container as anode and a graphite rod packed with manganese dioxide as cathode, giving about 1.5 volts. A lead-acid cell uses lead and lead dioxide plates in dilute sulphuric acid at about 2 volts, so a 12-volt car battery is six cells in series. A hydrogen-oxygen fuel cell produces only water.
Rusting is the same process, unwanted: iron oxidises in the presence of water and oxygen.
उपचयन-अपचयन, विद्युत अपघटन और सेल — इलेक्ट्रॉन वास्तव में कहाँ जाते हैं
What exams actually ask
SSC CGL and CHSL keep it to one line: which gas is liberated at the anode in brine electrolysis, what is galvanisation, what is the electrolyte in a lead storage battery. The trap is the sign of the electrodes — a question that says 'positive electrode' rather than 'anode' is testing whether you know the sign flips between the two kinds of cell.
RRB NTPC and Group D favour applications: which metal coats galvanised iron, why food cans are tin-plated, what a sacrificial anode does.
BPSC TRE-4 and other State services set statement pairs — 'the oxidising agent is itself oxidised' is the standard false statement.
CTET and the State TETs frame it as classroom demonstration items: what a nail in copper sulphate solution shows, why the blue colour fades.
UPSC Prelims prefers the industrial angle — cryolite's role in aluminium extraction, or why the process is so power-hungry.
उपचयन-अपचयन, विद्युत अपघटन और सेल — इलेक्ट्रॉन वास्तव में कहाँ जाते हैं
Points to Remember
• OIL RIG — Oxidation Is Loss, Reduction Is Gain. The two always occur together.
• The oxidising agent is itself reduced; the reducing agent is itself oxidised.
• Reduction at the cathode and oxidation at the anode, in every cell. Only the sign changes: electrolytic anode +, galvanic anode −.
• Oxidation numbers: free element 0, O usually −2, H usually +1, neutral compound sums to zero. S in H₂SO₄ is +6; Mn in KMnO₄ is +7.
• Electroplating: object at the cathode, coating metal at the anode. Electrorefining: impure metal at the anode.
• Brine electrolysis (chlor-alkali) → Cl₂ at anode, H₂ at cathode, NaOH in solution.
• Aluminium from alumina in molten cryolite; sodium from molten NaCl.
• Dry cell ≈ 1.5 V · lead-acid cell ≈ 2 V, so a 12 V battery has six cells. Fuel cell gives water only.
• Galvanisation = zinc coating. Sacrificial protection uses a more reactive metal such as zinc or magnesium.
⚠ Exam Tip 1: If a question names an electrode by charge instead of by name, translate it first. 'Positive electrode' means anode in electrolysis but cathode in a battery — the same words describe opposite plates.
⚠ Exam Tip 2: Rusting needs both water and oxygen. Any option offering only one of them, or offering carbon dioxide, is wrong — which is why oiling, painting and galvanising all work by keeping those two out.
विलयन की सांद्रता — मोलरता, मोललता, नॉर्मलता, ppm और विलयन बनाम विलायक का जाल
A solution has two parts: the solute, which dissolves, and the solvent, which does the dissolving. Together they are the solution. Concentration answers one question — how much solute sits in how much of what?
That last phrase is where marks are lost. Six different formulas exist because six different denominators are useful, and each formula names its own denominator precisely. Mass percentage divides by the solution. Molality divides by the solvent. Molarity divides by the volume of the solution, not the solvent. Mix two of them and you get a number that looks reasonable and is wrong, which is exactly what the distractors are built from.
So learn these formulas as denominator first, numerator second. If you can say what each one divides by, the arithmetic is one line and the trap options stop working. Everything in the next three cards is that one discipline applied six times.
विलयन की सांद्रता — मोलरता, मोललता, नॉर्मलता, ppm और विलयन बनाम विलायक का जाल
Mass percentage = (mass of solute ÷ mass of solution) × 100, where mass of solution = solute + solvent.
Dissolve 15 g of salt in 85 g of water. The solution weighs 100 g, so the answer is 15/100 × 100 = 15%. The standard wrong answer is 15/85 × 100 = 17.6%, produced by dividing by the water instead of by the whole solution. Notice that the numbers 15 and 85 were chosen so that the correct answer is the easy one — that is deliberate on the setter's part, and it is a gift you should take.
Volume percentage works the same way with volumes.
Parts per million = (mass of solute ÷ mass of solution) × 10⁶. It is mass percentage with 10⁶ instead of 100, used when the solute is too dilute for a percentage to read sensibly — pollutants, dissolved salts, trace metals.
The shortcut worth memorising: for dilute water solutions, 1 mg per kg = 1 mg per litre = 1 ppm.
विलयन की सांद्रता — मोलरता, मोललता, नॉर्मलता, ppm और विलयन बनाम विलायक का जाल
Molarity (M) = moles of solute ÷ volume of SOLUTION in litres. Unit: mol/L.
Dissolve 4 g of NaOH and make the solution up to 250 mL. Moles = 4 ÷ 40 = 0.1. Volume = 0.25 L. M = 0.1 ÷ 0.25 = 0.4 M. The trap is leaving the volume in millilitres and answering 0.1 — which is why 0.1 M appears as an option in almost every version of this question.
Molality (m) = moles of solute ÷ mass of SOLVENT in kilograms. Unit: mol/kg.
Dissolve 20 g of glucose, molar mass 180, in 180 g of water. Moles = 20 ÷ 180 = 0.111. Solvent = 0.18 kg. m = 0.111 ÷ 0.18 = 0.62 m. Using 200 g — the whole solution — gives 0.56, the classic distractor.
Why two units for one idea: heat a solution and its volume expands, so molarity falls even though nothing was added or removed. Mass does not expand. Molality is therefore temperature-independent, which is why freezing-point and boiling-point work always uses it.
विलयन की सांद्रता — मोलरता, मोललता, नॉर्मलता, ppm और विलयन बनाम विलायक का जाल
Normality (N) = gram equivalents of solute ÷ volume of solution in litres, and in practice N = M × n-factor.
The n-factor is basicity for an acid — replaceable H⁺ — so HCl is 1, H₂SO₄ is 2, H₃PO₄ is 3. For a base it is acidity, the number of OH⁻: NaOH is 1, Ca(OH)₂ is 2. For a salt it is the total positive charge. So 0.5 M H₂SO₄ is 0.5 × 2 = 1 N. Equivalent mass = molar mass ÷ n-factor.
Mole fraction x = moles of that component ÷ total moles of all components. It has no unit, and the fractions of all components add to exactly 1. Two moles of ethanol in eight moles of water gives x = 2 ÷ 10 = 0.2 for ethanol, so water must be 0.8. Dividing 2 by 8 is the common slip.
Dilution: adding solvent changes the volume but not the moles, so M₁V₁ = M₂V₂. Take 100 mL of 0.5 M and dilute to 500 mL: M₂ = (0.5 × 100) ÷ 500 = 0.1 M. In titration the same logic gives N₁V₁ = N₂V₂.
विलयन की सांद्रता — मोलरता, मोललता, नॉर्मलता, ppm और विलयन बनाम विलायक का जाल
What exams actually ask
BPSC TRE-4 asks this in the Part II Chemistry block and in Prelims General Science, mostly as a one-step molarity calculation with a clean molar mass — NaOH 40, NaCl 58.5, glucose 180 — or as the straight definition question, which term uses the solvent and which uses the solution.
SSC CGL and CHSL favour two items: the temperature-independence question, where molality is the answer and molarity is the trap, and a ppm conversion drawn from water quality, where the whole test is knowing that mg per litre and ppm are numerically the same for dilute water.
Railway NTPC and Group D stay at unit level — what is the unit of molarity, of molality, of mole fraction. Mole fraction having no unit is asked more often than its formula.
UPSC Prelims meets ppm in environment questions, where permissible limits for fluoride, arsenic and dissolved solids are quoted in mg/L and you are expected to read them as ppm without conversion.
CTET, Bihar STET and UP TET keep it classroom-level: concentrated versus dilute, saturated versus unsaturated, and one mass-percentage sum.
विलयन की सांद्रता — मोलरता, मोललता, नॉर्मलता, ppm और विलयन बनाम विलायक का जाल
Points to Remember
• Solution = solute + solvent. Every formula below differs only in what it divides by.
• Mass % = (mass of solute ÷ mass of SOLUTION) × 100.
• ppm = (mass of solute ÷ mass of SOLUTION) × 10⁶. For dilute water, 1 mg/kg = 1 mg/L = 1 ppm.
• Molarity M = moles ÷ litres of SOLUTION. Unit mol/L. Changes with temperature.
• Molality m = moles ÷ kilograms of SOLVENT. Unit mol/kg. Does NOT change with temperature.
• Normality N = M × n-factor. Acid → basicity, base → acidity, salt → total positive charge.
• Equivalent mass = molar mass ÷ n-factor. H₂SO₄: 98 ÷ 2 = 49.
• Mole fraction x = moles of one component ÷ TOTAL moles. No unit. All fractions sum to 1.
• Dilution M₁V₁ = M₂V₂; titration N₁V₁ = N₂V₂. Adding solvent never changes the number of moles.
• Molarity and mass % both use the solution; only molality uses the solvent alone.
⚠ Exam Tip 1: Before touching the numbers, write the denominator the formula demands and circle it in the question. Half the wrong options in a concentration numerical are the same calculation with the other denominator — 15/85 instead of 15/100, or 0.111/0.2 instead of 0.111/0.18. If you have already committed to which quantity goes below the line, the trap option cannot reach you.
⚠ Exam Tip 2: Check units before you check arithmetic. Molarity must come out in mol/L, so the volume has to be in litres — 250 mL is 0.25, not 250. Molality must come out in mol/kg, so the solvent has to be in kilograms — 180 g is 0.18, not 180. Two decimal shifts account for more lost marks in this chapter than any misunderstanding of chemistry.
बहुलक, प्लास्टिक, संश्लेषित रेशे, साबुन और अपमार्जक — रोज़मर्रा की वस्तुओं का रसायन
Look at three ordinary things and ask why they behave as they do.
An electrical switch is plastic, yet it does not soften when the wiring behind it warms up, while a plastic bucket left in the sun goes soft at the rim. A nylon rope holds a load that a cotton rope of the same thickness would not. A soap that lathers beautifully at home refuses to lather at all in a village well's water and leaves a grey deposit instead.
Each of those has a precise chemical reason, and each reason is worth a mark in a general awareness paper.
This is the most frequently examined chemistry in the whole of general studies, and the least demanding. There are no equations to balance and no calculations. What there is instead is a small vocabulary — polymer, monomer, thermoplastic, thermosetting, saponification, micelle — attached to materials you have handled since childhood.
Learn the reason behind each object rather than the object itself, and the questions answer themselves.
बहुलक, प्लास्टिक, संश्लेषित रेशे, साबुन और अपमार्जक — रोज़मर्रा की वस्तुओं का रसायन
A polymer is one very large molecule built by joining thousands of small identical units. The small unit is the monomer, and the joining process is polymerisation.
Nature makes polymers too. Cellulose in cotton and wood, starch in grain, proteins in wool and silk, and natural rubber are all natural polymers. What laboratories added was the ability to choose the monomer and therefore the properties.
Polythene is made from ethene, polyvinyl chloride from vinyl chloride, polystyrene from styrene, and Teflon from tetrafluoroethene — the non-stick coating on cookware. Bakelite, made from phenol and formaldehyde, was the first fully synthetic plastic.
The division that examiners care about is by behaviour on heating.
Thermoplastics soften when heated and can be melted and reshaped again and again — polythene, PVC, polystyrene, nylon. This is why plastic buckets and bottles can be recycled and why they deform in strong sun.
Thermosetting plastics set once and never soften again, because heat locks their chains together permanently. Bakelite and melamine are the examples, which is exactly why electrical switches, plug tops and pan handles are made of them.
बहुलक, प्लास्टिक, संश्लेषित रेशे, साबुन और अपमार्जक — रोज़मर्रा की वस्तुओं का रसायन
Fibres fall into three groups, and the middle group is where the marks are lost.
Natural fibres come from plants or animals. Cotton and jute are cellulose; wool and silk are protein. Silk is the only natural fibre that arrives as a continuous filament rather than as short staples.
Semi-synthetic fibre means rayon, and rayon is the trap. It is made by dissolving and re-forming wood cellulose, so its raw material is natural but the fibre is manufactured. It is called artificial silk because it takes dye well and drapes like silk at a fraction of the cost — but it is not the first synthetic fibre, because it is not fully synthetic at all.
Fully synthetic fibres are built from petrochemical monomers. Nylon was the first of them: strong enough for parachutes, ropes and fishing nets, and stronger than a natural fibre of the same thickness. Polyester, sold as terylene or dacron, resists creasing and is the material of PET bottles. Acrylic imitates wool and is warmer for its weight.
Rubber sits alongside these. Natural rubber is soft and sticky in heat, so it is heated with sulphur to cross-link its chains — the process called vulcanisation, which is what makes a tyre possible.
बहुलक, प्लास्टिक, संश्लेषित रेशे, साबुन और अपमार्जक — रोज़मर्रा की वस्तुओं का रसायन
Soap is the sodium or potassium salt of a long-chain fatty acid. It is made by heating a fat or oil with an alkali such as sodium hydroxide, a reaction called saponification, which yields soap and glycerol. Sodium makes hard cake soap; potassium makes soft and liquid soaps.
The cleaning action depends on the shape of the molecule. One end is an ionic head that mixes with water; the other is a long hydrocarbon tail that mixes with oil and grease. In water, many soap molecules gather with their tails pointing inward around a droplet of dirt and their heads outward, forming a cluster called a micelle. The dirt is now wrapped in a water-friendly shell and rinses away.
Hard water contains dissolved calcium and magnesium salts. These react with soap to form an insoluble scum, so the soap is used up producing a grey deposit instead of lather, and the cleaning fails.
Detergents solve exactly this. A detergent is the sodium salt of a long-chain alkyl benzene sulphonic acid rather than of a fatty acid, and its calcium and magnesium salts stay soluble. That is the whole reason detergents work in hard water and soaps do not. Their disadvantage is that branched-chain detergents resist bacterial breakdown and cause foam in rivers, which is why straight-chain, biodegradable versions replaced them.
बहुलक, प्लास्टिक, संश्लेषित रेशे, साबुन और अपमार्जक — रोज़मर्रा की वस्तुओं का रसायन
What exams actually ask
SSC CGL, CHSL and MTS ask one everyday-chemistry question a shift, most often the monomer of a named plastic or the material of an ordinary object. Their trap is Teflon against polythene: both are made from small gaseous monomers, and a candidate who remembers only 'plastic from a gas' will pick ethene for the non-stick pan.
RRB NTPC and Group D favour the fibres, especially the first synthetic fibre and the raw material of rayon. The trap is rayon itself, offered as the answer to 'first synthetic fibre' because it is older and is nicknamed artificial silk.
BPSC TRE-4 Part II general studies asks the reason rather than the name — why a switch is bakelite, why soap fails in hard water, why a detergent does not.
UPSC Prelims links detergents to water pollution and biodegradability.
CTET environmental studies keeps to sorting and observation: which fabrics come from plants, which from animals, what happens to plastic waste.
The error that recurs across all of them is swapping the definitions of soap and detergent, since both are sodium salts and both clean.
बहुलक, प्लास्टिक, संश्लेषित रेशे, साबुन और अपमार्जक — रोज़मर्रा की वस्तुओं का रसायन
Points to Remember
• A polymer is made of repeating monomer units joined by polymerisation.
• Natural polymers: cellulose, starch, protein, natural rubber. Synthetic: polythene, PVC, Teflon, nylon, polyester, bakelite.
• Monomers to remember: polythene from ethene, PVC from vinyl chloride, Teflon from tetrafluoroethene, bakelite from phenol and formaldehyde.
• Thermoplastics soften and can be remoulded — polythene, PVC, polystyrene, nylon.
• Thermosetting plastics never soften again — bakelite and melamine, used for switches and handles.
• Bakelite was the first fully synthetic plastic.
• Cotton and jute are cellulose; wool and silk are protein. Silk is the only natural continuous filament.
• Rayon is semi-synthetic, made from wood cellulose, and is called artificial silk.
• Nylon was the first fully synthetic fibre — parachutes, ropes, nets.
• Polyester is terylene or dacron, and PET bottles are made from it.
• Vulcanisation is heating rubber with sulphur to make it hard and elastic.
• Soap is the sodium or potassium salt of a fatty acid, made by saponification of a fat with alkali, giving glycerol as well.
• Cleaning works through micelles — ionic head in water, hydrocarbon tail in oil.
• Soap forms an insoluble scum in hard water; detergents do not, because their calcium and magnesium salts are soluble.
⚠ Exam Tip 1: For any question about a plastic object, ask first whether the object is ever allowed to get hot. Switches, plug tops, pan handles and crockery must be thermosetting — bakelite or melamine — while buckets, bottles, pipes and bags are thermoplastic. The use of the object gives away the category before you have recalled a single chemical name.
⚠ Exam Tip 2: Keep one sentence ready to separate soap from detergent: soap is the salt of a fatty acid and fails in hard water, a detergent is the salt of a sulphonic acid and does not. Nearly every question in this area is that one contrast rephrased, and having the sentence ready removes the swap that costs most candidates the mark.
ईंधन, दहन तथा ज्वाला — ज्वलन ताप, ऊष्मीय मान और तीन क्षेत्र
Combustion is a chemical reaction in which a substance combines with oxygen and gives out heat, usually with light as well. Nothing burns without oxygen, which is why oxygen is called the supporter of combustion while the thing that burns is called combustible.
Three conditions must be met together for a fire to start. A combustible substance must be present. A supporter of combustion — oxygen from the air — must be available. And the substance must reach its ignition temperature, the lowest temperature at which it catches fire.
Remove any one and there is no fire, which is also the whole logic of putting one out. Take away the fuel, cut off the oxygen with a blanket or carbon dioxide, or bring the temperature below the ignition point with water. Fire fighting is these three conditions read backwards.
Substances with a very low ignition temperature that catch fire easily are called inflammable — petrol, alcohol and liquefied petroleum gas among them.
SSC CGL and CHSL, RRB NTPC and Group D, BPSC TRE-4 general science and the CTET science paper all draw on this chapter, and it is asked far more often than its size suggests.
ईंधन, दहन तथा ज्वाला — ज्वलन ताप, ऊष्मीय मान और तीन क्षेत्र
Combustion comes in three kinds, and the flame in three zones.
Rapid combustion is ordinary burning, as when gas burns at a stove. Spontaneous combustion happens without any external heat being applied — white phosphorus catching fire in air is the standard example. Explosion is combustion so fast that a large volume of gas and heat is released at once, as in fireworks.
Now the flame, which is the part most asked. A candle flame has three zones, and they run from coolest inside to hottest outside.
The innermost dark zone contains unburnt wax vapour. Almost no burning happens here, so it is the least hot part of the flame — a fact that surprises students, because it sits at the centre.
The middle luminous yellow zone is where partial combustion occurs. Carbon particles are left unburnt, glow white-hot, and it is this glow that gives the flame its yellow light. Moderately hot.
The outermost non-luminous blue zone has plenty of oxygen, so combustion is complete, and this is the hottest zone. Goldsmiths direct the outermost zone onto metal for exactly that reason, through a blowpipe.
ईंधन, दहन तथा ज्वाला — ज्वलन ताप, ऊष्मीय मान और तीन क्षेत्र
Calorific value is the number that ranks fuels. It is the heat produced by the complete combustion of one kilogram of a fuel, measured in kilojoules per kilogram.
The approximate figures worth carrying, rounded: cow dung cake about 6,000 to 8,000; wood about 17,000 to 22,000; coal about 25,000 to 33,000; biogas about 35,000 to 40,000; petrol, kerosene and diesel all around 45,000; CNG about 50,000; LPG about 55,000; and hydrogen about 150,000 kilojoules per kilogram — by far the highest of any fuel, which is the single most asked figure here.
An ideal fuel is not simply the one with the highest number. It should have a high calorific value, a moderate ignition temperature so that it neither refuses to light nor catches fire by accident, a controlled rate of burning, little ash and few harmful products, and it should be cheap, easily available and safe to store and carry. Hydrogen fails several of these despite its calorific value, which is why it has not replaced petrol.
Solid fuels are wood and coal; liquid fuels are petrol, diesel and kerosene; gaseous fuels are LPG, CNG and biogas. Gaseous fuels generally burn cleanest and are easiest to control.
ईंधन, दहन तथा ज्वाला — ज्वलन ताप, ऊष्मीय मान और तीन क्षेत्र
Coal, petroleum and the harm that burning does.
Coal is graded by how much carbon it holds, and the order is asked directly. Peat has the least, roughly half; lignite, the brown coal, comes next; bituminous is higher again and is the commonest household and industrial grade; and anthracite has the most carbon, is the hardest, and burns almost without smoke. More carbon means more heat and less smoke, so the quality order follows the carbon order exactly.
Heating coal in the absence of air is called destructive distillation, and it gives coke, coal tar and coal gas.
Petroleum, often called black gold, is separated in a refinery into petroleum gas, petrol, kerosene, diesel, lubricating oil, paraffin wax and bitumen, in that rough order as the boiling point rises.
Burning them has costs. Incomplete combustion produces carbon monoxide, which is poisonous and especially dangerous from a coal fire or heater in a closed room. Complete combustion produces carbon dioxide, which is not poisonous but is the main greenhouse gas. Sulphur and nitrogen oxides from coal and oil turn rain acidic. Unburnt carbon particles cause respiratory illness.
Water must never be used on an oil fire, because oil floats and spreads the flames, nor on an electrical fire, because water conducts. Carbon dioxide is the right agent for both.
ईंधन, दहन तथा ज्वाला — ज्वलन ताप, ऊष्मीय मान और तीन क्षेत्र
What exams actually ask.
SSC CGL and CHSL ask the flame zones and the calorific value ranking. The two facts they return to most are that the innermost zone is the coolest and that hydrogen has the highest calorific value of any fuel.
RRB NTPC and Group D prefer definitions and the fire-fighting logic — what ignition temperature means, why carbon dioxide works as an extinguisher, why water is wrong for an oil fire.
BPSC TRE-4 general science asks the coal series in order and the products of destructive distillation, and it likes the incomplete-versus-complete combustion contrast because carbon monoxide has a public-safety angle.
The CTET science paper keeps to the candle flame and the conditions needed for burning.
Three traps worth naming. The innermost zone assumed to be hottest because it is at the centre, when it is the coolest and barely burning at all. Carbon dioxide and carbon monoxide swapped — the dioxide is the greenhouse gas, the monoxide is the poison. And the coal order reversed, with anthracite placed at the bottom because peat sounds like a finished product; the order runs peat, lignite, bituminous, anthracite, with carbon rising all the way.
ईंधन, दहन तथा ज्वाला — ज्वलन ताप, ऊष्मीय मान और तीन क्षेत्र
Points to Remember
· Combustion needs three things together: a combustible substance, oxygen, and the ignition temperature.
· Ignition temperature is the lowest temperature at which a substance catches fire. Inflammable substances have very low ones.
· Types: rapid, spontaneous (white phosphorus), explosion.
· Candle flame zones: innermost dark (unburnt vapour, least hot), middle luminous yellow (partial combustion, glowing carbon), outermost blue (complete combustion, hottest).
· Calorific value = heat from complete combustion of 1 kg of fuel, in kilojoules per kilogram.
· Hydrogen has the highest calorific value, roughly 1,50,000 kJ/kg; LPG about 55,000; petrol about 45,000; wood about 17,000-22,000.
· An ideal fuel: high calorific value, moderate ignition temperature, controlled burning, low ash, cheap and safe to store.
· Coal order by carbon: peat, lignite, bituminous, anthracite — anthracite the best.
· Destructive distillation of coal gives coke, coal tar and coal gas.
· Incomplete combustion gives poisonous carbon monoxide; complete combustion gives carbon dioxide, the main greenhouse gas.
· Never water on an oil fire or an electrical fire; use carbon dioxide.
⚠ Exam Tip 1: Remember the flame zones by oxygen supply rather than by position. The outside touches the most air, so it burns most completely and is hottest; the centre touches none, so it barely burns and is coolest. Reasoning from oxygen gets the order right even if the diagram has faded from memory.
⚠ Exam Tip 2: When a question compares fuels, check which property it names. Highest calorific value is hydrogen every time, but 'best household fuel' or 'ideal fuel' is a different question, and there the answer is usually LPG or CNG because safety, cost and storage are being weighed too.
उत्प्रेरक तथा चार औद्योगिक प्रक्रियाएँ — हैबर, संपर्क, ऑस्टवाल्ड और सॉल्वे
Almost every chemical a country runs on — fertiliser, sulphuric acid, nitric acid, washing soda — is made by a named industrial process, and every one of those processes is really a story about a catalyst.
A catalyst is a substance that changes the speed of a reaction without being used up in it. At the end you can recover it, chemically unchanged. It works by offering the reaction an easier path — a lower activation energy — so that more of the colliding molecules have enough energy to actually react.
That single idea turns reactions which would take years into reactions that finish in seconds, and it is why four process names keep returning in general science papers: Haber, Contact, Ostwald and Solvay. Learn what each one makes and which catalyst it uses, and you have answered most of what is ever asked about industrial chemistry.
उत्प्रेरक तथा चार औद्योगिक प्रक्रियाएँ — हैबर, संपर्क, ऑस्टवाल्ड और सॉल्वे
Four words decide most catalyst questions.
Positive catalyst speeds a reaction up by lowering the activation energy. Negative catalyst, or inhibitor, slows one down — glycerol added to hydrogen peroxide stops it decomposing on the shelf. Promoter is not a catalyst at all; it makes the catalyst work better, the way molybdenum boosts iron in the Haber process. Catalytic poison destroys a catalyst's activity, which is why sulphur compounds ruin a platinum catalyst.
Enzymes are biological catalysts — protein molecules that run the body's reactions at ordinary body temperature.
Now the trap. A catalyst does not increase the yield of a reversible reaction. It speeds up the forward and the backward reaction by exactly the same factor, so equilibrium is reached sooner but sits in precisely the same place. Any option promising more product because of the catalyst is wrong.
उत्प्रेरक तथा चार औद्योगिक प्रक्रियाएँ — हैबर, संपर्क, ऑस्टवाल्ड और सॉल्वे
Five things change the speed of a reaction, and papers test them as everyday observations.
Temperature — roughly, a 10 °C rise doubles the rate. Milk spoils faster in summer for this reason.
Concentration or pressure — more particles per unit volume means more collisions. For gases, raising the pressure is raising the concentration.
Surface area — powdered calcium carbonate fizzes with acid far faster than a marble chip of the same mass, because only the surface can react. This is also why flour dust can explode while a sack of flour cannot burn quickly.
Catalyst — lowers the energy barrier.
Nature of the reactants — ionic reactions in solution are almost instant; covalent bonds must break first, so those reactions are slower.
Worked example: iron rusts slowly in dry air, faster in moist air, fastest in salty moist air. Concentration and the nature of the medium, both visible in one object.
उत्प्रेरक तथा चार औद्योगिक प्रक्रियाएँ — हैबर, संपर्क, ऑस्टवाल्ड और सॉल्वे
| Process | Makes | Catalyst |
|---|---|---|
| Haber | Ammonia, NH₃ | Finely divided iron, promoted by molybdenum |
| Contact | Sulphuric acid, H₂SO₄ | Vanadium pentoxide, V₂O₅ |
| Ostwald | Nitric acid, HNO₃ | Platinum gauze |
| Solvay | Sodium carbonate, Na₂CO₃ | No catalyst — ammonia is recycled |
Haber: N₂ + 3H₂ ⇌ 2NH₃, at about 200 atmospheres and 450–500 °C. The high pressure is deliberate — four molecules become two, so squeezing the mixture pushes it towards ammonia. The ammonia goes on to make urea.
Contact: the key step is 2SO₂ + O₂ ⇌ 2SO₃. The SO₃ is absorbed in concentrated sulphuric acid to give oleum, which is then diluted — never poured straight into water, which would throw up an uncontrollable mist.
Ostwald: ammonia is burnt over hot platinum to nitric oxide, which oxidises to NO₂ and dissolves in water as nitric acid.
Solvay: brine, limestone and ammonia give sodium bicarbonate, heated to washing soda.
उत्प्रेरक तथा चार औद्योगिक प्रक्रियाएँ — हैबर, संपर्क, ऑस्टवाल्ड और सॉल्वे
SSC CGL and CHSL ask the catalyst by name: 'Vanadium pentoxide is used in which process?' The standard trap is swapping V₂O₅ and platinum between the Contact and Ostwald processes — platinum was once used in the Contact process too, and papers exploit that history.
RRB NTPC and Group D ask what a process makes: 'Haber's process manufactures —' with nitric acid sitting in the options, because Ostwald starts from ammonia and students merge the two.
BPSC TRE-4 General Studies asks the concept — what a catalyst does to activation energy, or which factor does not affect the rate of a reaction.
UPSC Prelims frames it as a statement set, typically including the claim that a catalyst alters the position of equilibrium. That statement is false.
CTET and State TETs keep it classroom-shaped: why powdered chalk reacts faster with acid than a chalk stick.
And watch molybdenum — it is asked as the promoter, never as the catalyst.
उत्प्रेरक तथा चार औद्योगिक प्रक्रियाएँ — हैबर, संपर्क, ऑस्टवाल्ड और सॉल्वे
• Catalyst: changes the rate, is chemically unchanged at the end, and works by lowering activation energy.
• Positive catalyst speeds up · negative catalyst (inhibitor) slows down · promoter helps the catalyst · poison destroys it.
• Enzymes are biological catalysts.
• Haber → ammonia → iron catalyst, molybdenum promoter, about 200 atm and 450–500 °C.
• Contact → sulphuric acid → V₂O₅. Oleum is the intermediate; H₂SO₄ is called the King of Chemicals.
• Ostwald → nitric acid → platinum gauze, starting from ammonia.
• Solvay → sodium carbonate → brine, limestone and ammonia, with the ammonia recovered and reused.
• Rate depends on temperature, concentration or pressure, surface area, catalyst, and the nature of the reactants.
⚠ Exam Tip 1: If an option says a catalyst increases the yield or shifts the equilibrium of a reversible reaction, it is wrong — a catalyst only makes equilibrium arrive sooner.
⚠ Exam Tip 2: Read whether the question wants the catalyst or the promoter. Haber's catalyst is iron; molybdenum is only the promoter.
हाइड्रोजन, भारी जल तथा गैसों की पहचान — हर पूछी जाने वाली गैस का एक सूत्र और एक परीक्षण
Two or Three Marks Hidden in One Line
Open any General Science paper and you will find a question that reads like a laboratory instruction: "Which gas turns lime water milky?" or "A gas blackens lead acetate paper. Identify it." These carry full marks and take four seconds — if you have stored the gas, its formula and its identifying test as one unit rather than three.
That is the whole method of this topic. For every gas that appears in papers we fix three things together:
> name → formula → the one test that proves it
The same discipline applies to water. Water is not one fact but a small cluster: its anomalous expansion, its hardness and the two chemicals that remove each type, and the two look-alike compounds — heavy water (D₂O) and hydrogen peroxide (H₂O₂) — that examiners love to swap for plain H₂O.
Five cards, roughly twenty formulas. Learn them as pairs, never as a list.
हाइड्रोजन, भारी जल तथा गैसों की पहचान — हर पूछी जाने वाली गैस का एक सूत्र और एक परीक्षण
Hydrogen, and the Two Compounds That Impersonate Water
Hydrogen — H₂. Atomic number 1, the lightest element and the most abundant in the universe. Its three isotopes are pure recall marks:
| Isotope | Symbol | Neutrons |
|---|---|---|
| Protium | ¹H | 0 |
| Deuterium | ²H or D | 1 |
| Tritium | ³H or T | 2 (radioactive) |
Lab preparation: Zn + dilute H₂SO₄ → ZnSO₄ + H₂↑
Test: brings a burning splint to a 'pop' sound.
Heavy water — D₂O. Water in which both hydrogens are deuterium. Molar mass 20 (ordinary water 18), boiling point 101.4 °C, freezing point 3.8 °C. It is used as a moderator in nuclear reactors — it slows fast neutrons without absorbing many of them. Discovered by Harold Urey.
Hydrogen peroxide — H₂O₂. Antiseptic, bleaching agent, and the chemical used to restore darkened old oil paintings (it converts black PbS back to white PbSO₄). Light decomposes it into water and oxygen, which is why it is kept in dark or opaque bottles.
हाइड्रोजन, भारी जल तथा गैसों की पहचान — हर पूछी जाने वाली गैस का एक सूत्र और एक परीक्षण
Water — Anomalous Expansion, and the Two Hardnesses
H₂O. Cool water and it contracts like any liquid — until 4 °C. Below that it expands. So water is densest at 4 °C (1 g/cm³), ice is lighter than water and floats, and a frozen pond keeps liquid water at 4 °C at the bottom where fish survive. That is anomalous expansion, and it is why a bottle of water cracks in a freezer.
Water also carries the highest specific heat of common liquids — 1 cal/g °C (4.18 J/g °C) — which is why it is used as a coolant. Latent heat of fusion 80 cal/g; latent heat of vaporisation 540 cal/g.
Hardness is dissolved calcium and magnesium salts. Hard water refuses to lather with soap because it forms an insoluble scum.
| Type | Caused by | Removed by |
|---|---|---|
| Temporary | Bicarbonates — Ca(HCO₃)₂, Mg(HCO₃)₂ | Boiling, or Clark's method — slaked lime Ca(OH)₂ |
| Permanent | Sulphates and chlorides — CaSO₄, MgSO₄, CaCl₂, MgCl₂ | Washing soda Na₂CO₃, permutit (zeolite), ion-exchange resin |
Boiling removes only temporary hardness. Washing soda removes both.
हाइड्रोजन, भारी जल तथा गैसों की पहचान — हर पूछी जाने वाली गैस का एक सूत्र और एक परीक्षण
The Gas Table — Formula and Test as One Unit
| Gas | Formula | Identifying test |
|---|---|---|
| Oxygen | O₂ | Relights a glowing splint |
| Hydrogen | H₂ | 'Pop' with a burning splint |
| Carbon dioxide | CO₂ | Turns lime water milky; excess CO₂ clears it again |
| Ammonia | NH₃ | Pungent; moist red litmus → blue; dense white fumes with an HCl rod |
| Hydrogen sulphide | H₂S | Rotten-egg smell; blackens lead acetate paper |
| Sulphur dioxide | SO₂ | Pungent; turns acidified potassium dichromate paper orange → green |
| Chlorine | Cl₂ | Greenish-yellow; bleaches moist litmus; starch-iodide paper → blue |
| Nitrogen dioxide | NO₂ | Reddish-brown, pungent |
| Carbon monoxide | CO | Colourless, odourless, highly poisonous |
Three of these earn extra questions on their own:
हाइड्रोजन, भारी जल तथा गैसों की पहचान — हर पूछी जाने वाली गैस का एक सूत्र और एक परीक्षण
What Exams Actually Ask
SSC CGL / CHSL / MTS ask the test in reverse — they describe the observation and want the gas. "A gas turns lime water milky" (CO₂) and "a gas blackens lead acetate paper" (H₂S) are the two that repeat most. SSC also loves heavy water = D₂O with H₂O₂ planted beside it as a distractor.
RRB NTPC / Group D prefer the common names: laughing gas, marsh gas, dry ice, water gas. They also ask which gas is used as a moderator-related fact — note the moderator is heavy water, a liquid, not a gas, and options often blur that.
BPSC and state PSCs favour hardness. The classic trap: "Temporary hardness is removed by boiling" is true, but an option reading "Permanent hardness is removed by boiling" is planted beside it. Washing soda removes both; boiling removes only temporary.
UPSC Prelims asks why — why ice floats, why CO is more dangerous than CO₂ in a closed room (CO₂ warns you by choking, CO gives no warning at all).
CTET-style classroom questions ask which gas makes the lime water in a school demonstration turn milky when a child breathes through a straw.
हाइड्रोजन, भारी जल तथा गैसों की पहचान — हर पूछी जाने वाली गैस का एक सूत्र और एक परीक्षण
Points to Remember
⚠ Exam Tip 1: If an option says permanent hardness is removed by boiling, it is wrong — every time. Boiling only breaks down bicarbonates. Washing soda (Na₂CO₃) is the answer whenever the question asks for one chemical that handles both kinds of hardness.
⚠ Exam Tip 2: Do not let H₂O₂ and D₂O share a slot in your memory. D₂O is heavy water — a nuclear moderator. H₂O₂ is hydrogen peroxide — an antiseptic that light destroys. Examiners place them as adjacent options precisely because the symbols look alike at speed.
संयोजकता एवं मूलक — क्रिस-क्रॉस विधि जो हर रासायनिक सूत्र बना देती है
One Rule Writes Every Formula
Ask a Class 8 student to write the formula for aluminium oxide and most reach for memory. There is no need to memorise — there is one rule.
Valency is the combining capacity of an element or radical: how many hydrogen atoms (or their equivalent) one atom of it can combine with. It comes directly from the electrons in the outermost shell — the same shell that decides where an element sits in the periodic table and how badly it wants to complete its octet of eight.
A metal loses electrons to empty its outer shell, so its valency equals the electrons it gives away. A non-metal gains electrons to fill its outer shell, so its valency equals the electrons it takes. Once you know an atom's valency, you don't calculate a formula — you write it, in seconds, every time.
संयोजकता एवं मूलक — क्रिस-क्रॉस विधि जो हर रासायनिक सूत्र बना देती है
The Valency You Must Know Cold
Most elements exams test have fixed valency. Learn these once: hydrogen, sodium, potassium, silver — all +1. Oxygen, calcium, magnesium, zinc, barium — all +2. Aluminium, boron — +3. Carbon and silicon — +4 (and sometimes +2 for carbon). Nitrogen swings between +3 and +5 depending on the compound.
A smaller group has variable valency — mostly transition and post-transition metals. Iron forms Fe2+ (ferrous) and Fe3+ (ferric). Copper forms Cu+ (cuprous) and Cu2+ (cupric). Lead and tin behave the same way, with a lower and a higher state.
Papers name the compound by the valency used — ferrous sulphate is Fe2+, ferric chloride is Fe3+ — so the Latin-derived name itself is telling you which formula to write, if you know the -ous/-ic pattern: lower valency takes -ous, higher takes -ic.
संयोजकता एवं मूलक — क्रिस-क्रॉस विधि जो हर रासायनिक सूत्र बना देती है
Radicals — Groups That Behave Like One Atom
A radical is a group of atoms that carries a charge and moves through a reaction as a single unit, exactly like an ion. Exams expect instant recall of these:
Charge -1: hydroxide OH-, nitrate NO3-, bicarbonate HCO3-, chloride Cl- (a simple radical, not compound).
Charge -2: sulphate SO4(2-), carbonate CO3(2-), sulphite SO3(2-).
Charge -3: phosphate PO4(3-).
Charge +1: ammonium NH4+ — the only common positive compound radical.
Notice the pattern inside the names: '-ate' means the radical containing more oxygen (sulphate, SO4 2-); '-ite' means one oxygen fewer (sulphite, SO3 2-). That single letter is worth marks on its own in a 'name the radical' question, and it is the detail most students blur under time pressure.
संयोजकता एवं मूलक — क्रिस-क्रॉस विधि जो हर रासायनिक सूत्र बना देती है
The Criss-Cross Method, Step by Step
Write the symbols side by side, metal (or ammonium) first, radical second. Take each valency and drop it as the other one's subscript — that's the 'criss-cross.' Then simplify the ratio to its lowest terms.
Calcium phosphate: Ca is +2, phosphate PO4 is -3. Cross them: Ca3(PO4)2. The subscripts 3 and 2 don't share a common factor, so this is final.
Aluminium sulphate: Al is +3, sulphate SO4 is -2. Cross them: Al2(SO4)3.
Ammonium carbonate: NH4 is +1, carbonate CO3 is -2. Cross them: (NH4)2CO3 — brackets appear whenever a radical needs a subscript greater than 1.
Calcium oxide: Ca is +2, O is -2. Crossing gives Ca2O2 — but 2:2 simplifies to 1:1, so the correct formula is CaO. Skipping this last step is the single most common formula-writing mistake in the exam hall.
संयोजकता एवं मूलक — क्रिस-क्रॉस विधि जो हर रासायनिक सूत्र बना देती है
What Exams Actually Ask
BPSC TRE-4 and CTET general science routinely give a compound name and ask for the formula, or the reverse — a formula and ask for the name — testing the same criss-cross skill in both directions.
SSC and Railway general science favour matching-type questions: valency of an element/radical matched against its symbol, or 'which of these compounds is correctly written' with three formulas that forgot to simplify the ratio.
The most repeated trap across all these exams is exactly the CaO mistake above — a technically 'crossed' formula that was never reduced to lowest terms. A close second is confusing valency with charge sign for variable-valency metals: writing Fe3+ compounds using Fe2+'s formula because the question named the metal without the ferrous/ferric clue and the student defaulted to the more familiar valency.
UPSC-level general science rarely asks formula-writing directly but expects the same table for balancing equations.
संयोजकता एवं मूलक — क्रिस-क्रॉस विधि जो हर रासायनिक सूत्र बना देती है
Points to Remember
⚠ Exam Tip 1: If your crossed formula has both subscripts sharing a common factor, you are not done — divide it out before you write the final answer.
⚠ Exam Tip 2: '-ous' and '-ite' both mean the lower option (lower valency, fewer oxygens); '-ic' and '-ate' both mean the higher option. Pair them and you'll never confuse ferrous sulphite with ferric sulphate again.
धातुओं का निष्कर्षण — अयस्क, भर्जन, निस्तापन, प्रगलन और विद्युत-अपघटनी शोधन
From Rock to Metal — Why the Route Changes
Most metals are not found free in nature. They occur as minerals, and a mineral from which a metal can be extracted profitably is called an ore. Every ore is a mineral, but not every mineral is an ore. Only the least reactive metals — gold, platinum, and sometimes silver and copper — are found in the free, native state.
The whole subject of metallurgy follows one rule: the method of extraction depends on the metal's position in the reactivity series. Low-reactivity metals can be freed just by heating; middle-reactivity metals need a reducing agent such as carbon; and highly reactive metals hold on to their partners so tightly that only electrolysis can pull them apart.
This topic follows real metals through that route as case studies, because exams test exactly this reasoning — which step, which metal, and why.
धातुओं का निष्कर्षण — अयस्क, भर्जन, निस्तापन, प्रगलन और विद्युत-अपघटनी शोधन
Step One — Concentrating the Ore
Mined ore is mixed with sand, clay and rock, together called gangue. The first job is to remove it, and the method depends on how the ore differs from the gangue.
Froth flotation is used for sulphide ores such as zinc blende (ZnS), galena (PbS) and copper pyrites. The powdered ore is mixed with water and pine oil and air is blown through; the sulphide particles are wetted by the oil and float up with the froth, while the gangue, wetted by water, sinks.
Gravity separation (hydraulic washing) uses the fact that heavy ore particles settle faster than light gangue in running water. Magnetic separation pulls out a magnetic ore such as magnetite (Fe₃O₄) or separates tinstone from wolframite. For bauxite, a chemical method — leaching with sodium hydroxide — dissolves the alumina and leaves impurities behind.
धातुओं का निष्कर्षण — अयस्क, भर्जन, निस्तापन, प्रगलन और विद्युत-अपघटनी शोधन
Step Two — Roasting vs Calcination, and Reduction
Before reduction, the ore is usually converted into an oxide, because oxides are easier to reduce. Two heating processes do this, and exams love to swap them.
Roasting heats a sulphide ore strongly in excess air: 2ZnS + 3O₂ → 2ZnO + 2SO₂. The giveaway is sulphur dioxide gas.
Calcination heats a carbonate (or hydrated) ore in a limited supply of air or none: ZnCO₃ → ZnO + CO₂. The giveaway is carbon dioxide or water vapour.
Case study — zinc: zinc blende is roasted, calamine is calcined, and both give ZnO, which is then reduced with carbon (coke): ZnO + C → Zn + CO.
Case study — mercury: cinnabar (HgS) needs no carbon at all. Roasting gives HgO, and simply heating it further releases mercury, because mercury sits so low in the reactivity series.
धातुओं का निष्कर्षण — अयस्क, भर्जन, निस्तापन, प्रगलन और विद्युत-अपघटनी शोधन
Step Three — Electrolysis for Reactive Metals, Then Refining
Sodium, potassium, calcium, magnesium and aluminium are more reactive than carbon, so carbon cannot take oxygen away from them. They are extracted by electrolysis of their molten compounds. Sodium comes from molten sodium chloride: sodium collects at the cathode and chlorine at the anode.
Case study — aluminium: bauxite is purified to alumina (Al₂O₃), which melts above 2000 °C. It is dissolved in molten cryolite to lower the melting point and save energy, then electrolysed (the Hall–Héroult process). Aluminium forms at the cathode. This heavy electricity demand is why aluminium plants are built near cheap power.
The metal obtained is still impure, so it is refined. In electrolytic refining, the impure metal is the anode, a thin strip of pure metal is the cathode, and a salt solution of the metal is the electrolyte. Pure metal deposits on the cathode; insoluble impurities fall below the anode as anode mud. Copper, zinc and silver are refined this way.
धातुओं का निष्कर्षण — अयस्क, भर्जन, निस्तापन, प्रगलन और विद्युत-अपघटनी शोधन
What Exams Actually Ask
SSC CGL/CHSL and Railway NTPC/Group D lean heavily on ore–metal matching: bauxite–aluminium, haematite–iron, galena–lead, cinnabar–mercury, zinc blende and calamine–zinc. They also ask the single-process questions: which process uses excess air, which ore is concentrated by froth flotation, what cryolite does. UPSC Prelims tends to frame it as statements — for example, that aluminium is obtained by electrolysis because carbon cannot reduce alumina. BPSC TRE-4 General Studies and CTET's science content ask the reactivity-based reasoning: why sodium cannot be made with coke, or why gold occurs native.
The classic traps: swapping roasting and calcination (remember: roasting = sulphide + excess air, calcination = carbonate + little or no air); thinking cryolite is an ore of aluminium rather than a solvent that lowers the melting point; and placing the pure metal at the anode in electrolytic refining — it is always the impure metal that is the anode.
धातुओं का निष्कर्षण — अयस्क, भर्जन, निस्तापन, प्रगलन और विद्युत-अपघटनी शोधन
Points to Remember
⚠ Exam Tip 1: Look at the gas released — SO₂ means roasting, CO₂ means calcination. The ore's anion tells you the process.
⚠ Exam Tip 2: If a metal lies above carbon in the reactivity series, the answer is electrolysis; carbon reduction is never correct for sodium, magnesium or aluminium.
औषधियों में रसायन — पीड़ाहारी, ज्वरनाशी, प्रतिजैविक, पूतिरोधी, विसंक्रामी और प्रतिअम्ल
Why Medicines Are a Chemistry Topic
Every medicine is a chemical chosen for what it does to the body, so exams classify drugs by action, not by brand: does it relieve pain, lower fever, kill bacteria, protect a wound or neutralise acid? Learn the classes and their standard examples, and most questions answer themselves.
Two ideas cause most mistakes. First, one drug can belong to several classes — aspirin relieves pain, lowers fever, reduces inflammation and thins the blood. Second, the same substance can change class with concentration: a 0.2% phenol solution is an antiseptic, while a 1% solution is a disinfectant.
This topic covers the six classes papers ask about most — analgesics, antipyretics, antibiotics, antiseptics, disinfectants and antacids — plus the few names from tranquillisers and antihistamines that keep reappearing.
औषधियों में रसायन — पीड़ाहारी, ज्वरनाशी, प्रतिजैविक, पूतिरोधी, विसंक्रामी और प्रतिअम्ल
Pain and Fever — Analgesics and Antipyretics
Analgesics reduce pain without causing unconsciousness. They come in two groups.
Non-narcotic analgesics — aspirin, paracetamol, ibuprofen — relieve mild to moderate pain and are not habit-forming.
Narcotic analgesics — morphine and codeine, obtained from opium — relieve severe pain, such as after surgery, but produce sleep and dependence in larger doses. Heroin is a derivative of morphine.
Antipyretics lower body temperature in fever. Paracetamol and aspirin are both analgesic and antipyretic.
Aspirin is acetylsalicylic acid. Beyond pain and fever, it reduces inflammation and stops platelets from clumping, which is why it is also described as an anti-clotting drug. Its known drawback is irritation of the stomach lining. Paracetamol relieves pain and fever but has little anti-inflammatory action — the difference between the two is a frequent one-mark question.
औषधियों में रसायन — पीड़ाहारी, ज्वरनाशी, प्रतिजैविक, पूतिरोधी, विसंक्रामी और प्रतिअम्ल
Antibiotics — Killing Bacteria, Not Viruses
An antibiotic is a substance, first obtained from micro-organisms, that kills bacteria or stops their growth. Alexander Fleming discovered penicillin in 1928 from the mould Penicillium. Earlier, Paul Ehrlich had developed Salvarsan, an arsenic compound used against syphilis, which is why he is called the father of chemotherapy. Selman Waksman discovered streptomycin, used against tuberculosis.
Two classifications matter:
• By effect — bactericidal drugs kill bacteria (penicillin, ofloxacin, aminoglycosides); bacteriostatic drugs stop them multiplying (erythromycin, tetracycline, chloramphenicol).
• By range — broad-spectrum drugs act on many kinds of bacteria (chloramphenicol, tetracycline, ampicillin, amoxicillin); narrow-spectrum drugs act on a few (penicillin G).
Antibiotics have no effect on viruses, so they do not cure the common cold or influenza. Overuse lets resistant bacteria survive and spread — the problem called antibiotic resistance.
औषधियों में रसायन — पीड़ाहारी, ज्वरनाशी, प्रतिजैविक, पूतिरोधी, विसंक्रामी और प्रतिअम्ल
Antiseptics, Disinfectants and Antacids
Antiseptics kill or stop micro-organisms on living tissue — wounds, cuts, skin. Examples: Dettol (chloroxylenol and terpineol), tincture of iodine (2–3% iodine in an alcohol–water mixture), boric acid (dilute, for the eyes) and iodoform.
Disinfectants do the same on non-living objects — floors, drains, instruments — and are too harsh for skin. Examples: 1% phenol, chlorine at 0.2–0.4 ppm in drinking water, and sulphur dioxide in very low concentration.
The classic case: phenol at 0.2% is an antiseptic, at 1% a disinfectant. Concentration, not the chemical, decides the class.
Antacids neutralise excess hydrochloric acid in the stomach. Examples: sodium hydrogencarbonate (baking soda), magnesium hydroxide (milk of magnesia) and aluminium hydroxide. Metal hydroxides are preferred because they are insoluble and do not push the pH above neutral. Cimetidine and ranitidine work differently — they block histamine from triggering acid release.
औषधियों में रसायन — पीड़ाहारी, ज्वरनाशी, प्रतिजैविक, पूतिरोधी, विसंक्रामी और प्रतिअम्ल
What Exams Actually Ask
SSC CGL, CHSL and MTS — match the drug to its class, and the chemical or common name: aspirin = acetylsalicylic acid, milk of magnesia = magnesium hydroxide. The trap is a near-name: salicylic acid for aspirin, or magnesium sulphate (Epsom salt) for milk of magnesia.
Railway NTPC and Group D — discoverers (Fleming and penicillin) and the antiseptic–disinfectant split. The distractor for Fleming is usually Pasteur or Ehrlich.
BPSC TRE-4 (General Science) — everyday classes: which drug is an antacid, which is an antipyretic, why antibiotics fail against a cold.
CTET science — classroom-framed questions on antacids and neutralisation, set at the Class 7 acids-and-bases level.
UPSC Prelims — antibiotic resistance and why antibiotics do not act on viruses, usually as statements to be marked true or false.
औषधियों में रसायन — पीड़ाहारी, ज्वरनाशी, प्रतिजैविक, पूतिरोधी, विसंक्रामी और प्रतिअम्ल
Points to Remember
• Analgesic = pain relief. Non-narcotic: aspirin, paracetamol, ibuprofen. Narcotic: morphine, codeine (from opium).
• Antipyretic = lowers fever: paracetamol, aspirin.
• Aspirin = acetylsalicylic acid; also anti-inflammatory and anti-clotting.
• Penicillin — Fleming, 1928. Salvarsan — Ehrlich. Streptomycin — Waksman.
• Bactericidal: penicillin, ofloxacin. Bacteriostatic: erythromycin, tetracycline, chloramphenicol.
• Antibiotics do not work on viruses.
• Antiseptic = living tissue (Dettol, tincture of iodine, boric acid). Disinfectant = non-living objects (1% phenol, chlorine).
• Antacids: NaHCO₃, Mg(OH)₂ (milk of magnesia), Al(OH)₃; cimetidine and ranitidine block histamine.
• Tranquillisers: equanil, barbiturates. Antihistamines: brompheniramine, terfenadine.
⚠ Exam Tip 1: If a question gives a concentration, the answer turns on it — 0.2% phenol is an antiseptic, 1% phenol a disinfectant.
⚠ Exam Tip 2: For aspirin, reject salicylic acid; for milk of magnesia, reject magnesium sulphate — both are the planted near-names.
सीमेंट, काँच, मृत्तिका और उर्वरक: कच्चा माल, संघटन और उपयोग
Four Materials You See Every Day
The house you live in, the window in its wall, the plate you eat from and the grain on that plate all depend on four families of chemical materials: cement, glass, ceramics and fertilisers. Exam setters love them because every question has a short, factual answer: what is it made from, what is added to it, and what is it used for.
Cement binds bricks and stones; glass is a transparent, brittle, non-crystalline solid made from sand; ceramics are hard, heat-resistant objects made by firing clay; and fertilisers feed plants with nitrogen, phosphorus and potassium.
For each material, store three things: the raw materials, one special additive or property, and one use. For example, cement: limestone and clay, gypsum added at the end, and it sets by reacting with water. That template is enough to answer most SSC, Railway, CTET and BPSC TRE-4 questions on this topic.
सीमेंट, काँच, मृत्तिका और उर्वरक: कच्चा माल, संघटन और उपयोग
Cement: Limestone, Clay and a Pinch of Gypsum
Ordinary Portland cement, patented by Joseph Aspdin in 1824, is made from limestone (calcium carbonate) and clay (silica and alumina). The mixture is heated in a rotary kiln to about 1400 to 1450 degrees Celsius, where it partly fuses into hard lumps called clinker. The clinker is ground to a fine powder, and 2 to 3 percent gypsum is added at this last step.
Gypsum is a retarder. Without it, cement would set almost instantly and could not be worked. Setting is not drying: it is a chemical reaction called hydration, which is why cement hardens even under water.
Mortar is cement, sand and water, used between bricks. Concrete is cement, sand, gravel or stone chips and water. Reinforced cement concrete (RCC) adds steel bars, because concrete resists compression well but tension poorly.
Remember the order: limestone and clay, kiln, clinker, grind, add gypsum.
सीमेंट, काँच, मृत्तिका और उर्वरक: कच्चा माल, संघटन और उपयोग
Glass and Ceramics
Ordinary soda-lime glass is made by melting sand (silica), soda ash (sodium carbonate) and limestone at about 1500 degrees Celsius. On cooling it does not crystallise, so it is an amorphous solid, sometimes loosely called a super-cooled liquid. Slow cooling, called annealing, removes internal stress.
Varieties matter for exams. Borosilicate glass (Pyrex) contains boron oxide, expands very little on heating and is used for laboratory ware and ovenware. Lead glass (crystal glass) has a high refractive index and sparkle, so it is used in cut glass and optical lenses. Colour comes from metal oxides: cobalt gives blue, chromium gives green and copper(I) oxide gives ruby red.
Ceramics are made by shaping clay (kaolin, or china clay, for porcelain) and firing it at high temperature. Pottery, bricks, tiles, porcelain and insulators are ceramics. They are hard and heat-resistant but brittle.
सीमेंट, काँच, मृत्तिका और उर्वरक: कच्चा माल, संघटन और उपयोग
Fertilisers: N, P and K
Plants need three major nutrients. Nitrogen (N) drives leaf and shoot growth, phosphorus (P) helps roots and flowering, and potassium (K) builds disease resistance and strength. Fertilisers supply them, and a bag labelled NPK shows the three in that order.
Urea, CO(NH₂)₂, has the highest nitrogen content of the common fertilisers at 46 percent, which is why it is the most used in India. Ammonium nitrate holds about 35 percent N and ammonium sulphate about 21 percent. Diammonium phosphate (DAP) supplies both nitrogen and phosphorus. Muriate of potash (potassium chloride) supplies potassium. Superphosphate supplies phosphorus.
A historical fact examiners enjoy: urea was the first organic compound made in a laboratory from an inorganic source. Friedrich Wöhler prepared it in 1828 by heating ammonium cyanate, and it ended the belief in vital force.
Overusing fertilisers leaches nitrates into water and causes algal blooms, so balance matters.
सीमेंट, काँच, मृत्तिका और उर्वरक: कच्चा माल, संघटन और उपयोग
What Exams Actually Ask
SSC CGL, CHSL and MTS ask the raw materials of glass and cement, the purpose of gypsum, the fertiliser with the highest nitrogen, and the colouring oxide for a given glass colour. Railway NTPC and Group D repeat the same facts, usually as a one-line fill-in: gypsum retards setting, urea is 46% N. BPSC TRE-4 general science asks composition and uses, and sometimes the type of glass for laboratory ware. CTET items are classroom-framed, for example a teacher asking why a laboratory beaker is made of borosilicate glass or why a farmer is told to use balanced NPK.
The recurring traps: saying gypsum increases strength or adds colour when it only delays setting; calling setting 'drying'; listing clay instead of soda ash as a glass ingredient; confusing borosilicate (heat-resistant) with lead glass (high refractive index); picking DAP or ammonium nitrate for highest nitrogen instead of urea; and forgetting that DAP carries phosphorus as well as nitrogen.
Attach one signature fact to every material and the options sort themselves.
सीमेंट, काँच, मृत्तिका और उर्वरक: कच्चा माल, संघटन और उपयोग
Points to Remember
⚠ Exam Tip 1: If an option says gypsum 'increases strength', 'adds colour' or 'makes cement waterproof', reject it; its only job is to retard setting.
⚠ Exam Tip 2: For highest nitrogen choose urea (46%); for 'N and P together' choose DAP; for potassium choose muriate of potash.
एथेनॉल और एथेनॉइक अम्ल: सोडियम परीक्षण, ऑक्सीकरण, निर्जलीकरण, एस्टरीकरण और साबुनीकरण
Two Carbon Compounds, Five Reactions
Ethanol (C₂H₅OH) and ethanoic acid (CH₃COOH) are the two carbon compounds that appear again and again in science papers. Both are everyday substances: ethanol is the alcohol in spirit, sanitisers and fuel blends, and ethanoic acid is the sour part of vinegar. What separates them is a functional group. Ethanol carries −OH (alcohol) and ethanoic acid carries −COOH (carboxylic acid). Almost every question asks what each one does with sodium, with a carbonate or bicarbonate, with an oxidising agent, with concentrated sulphuric acid, or with the other compound. If you can write five equations and remember one observation for each, you can answer nearly every item on this topic. This short builds them in order: ethanol's properties and reactions, ethanoic acid's properties, then esterification and saponification, and finally the traps exams set around them.
एथेनॉल और एथेनॉइक अम्ल: सोडियम परीक्षण, ऑक्सीकरण, निर्जलीकरण, एस्टरीकरण और साबुनीकरण
Ethanol: Properties and Three Reactions
Ethanol is a colourless liquid with a pleasant smell, fully miscible with water, and neutral to litmus: it does not turn litmus red or blue. It is made industrially by fermentation, where yeast enzymes (zymase) convert sugar to ethanol and carbon dioxide.
Reaction 1, with sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑. Sodium ethoxide forms and hydrogen bubbles off. Water also gives this reaction, which is why only the correct test comes next.
Reaction 2, oxidation: heated with alkaline potassium permanganate or acidified potassium dichromate, ethanol becomes ethanoic acid. The orange dichromate turns green.
Reaction 3, dehydration: heated with excess concentrated sulphuric acid at 443 K (170 °C), ethanol loses water and forms ethene: C₂H₅OH → C₂H₄ + H₂O. The acid acts as a dehydrating agent and is not used up.
एथेनॉल और एथेनॉइक अम्ल: सोडियम परीक्षण, ऑक्सीकरण, निर्जलीकरण, एस्टरीकरण और साबुनीकरण
Ethanoic Acid: A Weak Acid with a Sour Smell
Ethanoic acid (acetic acid) is a colourless liquid with a sharp smell. Vinegar is a 5–8% solution of it in water. Pure ethanoic acid freezes at 290 K (16.6 °C), so on cold days it solidifies into ice-like crystals; this is why it is called glacial acetic acid.
It is a weak acid: it turns blue litmus red but ionises only slightly in water. Its reactions with bases and carbonates are the ones exams use.
With sodium carbonate: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂↑. With sodium hydrogencarbonate: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑. Both give brisk effervescence of carbon dioxide that turns lime water milky.
With sodium hydroxide it neutralises: CH₃COOH + NaOH → CH₃COONa + H₂O.
Ethanol shows no effervescence with sodium hydrogencarbonate, so this is the clean test to tell the acid from the alcohol.
एथेनॉल और एथेनॉइक अम्ल: सोडियम परीक्षण, ऑक्सीकरण, निर्जलीकरण, एस्टरीकरण और साबुनीकरण
Esterification, Saponification and Denatured Spirit
When ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, they form an ester and water: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. The ester is ethyl ethanoate, a sweet, fruity-smelling liquid used in perfumes and flavourings. The sulphuric acid acts as a catalyst and dehydrating agent, and the reaction is reversible.
When an ester is heated with sodium hydroxide, the reaction runs the other way into the sodium salt of the acid and the alcohol. This alkaline breakdown is called saponification, and it is how soap is made from fats, which are esters of glycerol.
Denatured spirit is ethanol made unfit to drink by adding poisonous methanol, often with a blue dye. Methanol can cause blindness and death, so denaturing keeps cheap industrial alcohol out of drinks and from tax evasion.
एथेनॉल और एथेनॉइक अम्ल: सोडियम परीक्षण, ऑक्सीकरण, निर्जलीकरण, एस्टरीकरण और साबुनीकरण
What Exams Actually Ask
BPSC TRE-4 science sections, SSC CGL, CHSL and MTS general science, Railway NTPC and Group D, and UPSC prelims-style questions all draw from this pair. CTET-style science items frame it as vinegar, spirit and soap in everyday settings. These questions are AI-written for practice, not copied from any past paper, but they follow the patterns such papers use.
Trap patterns: (1) offering 'reacts with sodium to give hydrogen' as a test for ethanoic acid versus ethanol, when both do it; (2) naming carbon dioxide as the gas from ethanol with sodium; (3) confusing the temperature of dehydration (443 K, ethene) with other conditions; (4) calling alkaline hydrolysis of an ester 'esterification'; (5) believing vinegar is citric acid because it is sour; (6) mixing up 'glacial' with a glacier or with ice being present, when it refers to pure acid freezing below 16.6 °C. Whenever a question names the reagent, recall the observation tied to it before looking at the options.
एथेनॉल और एथेनॉइक अम्ल: सोडियम परीक्षण, ऑक्सीकरण, निर्जलीकरण, एस्टरीकरण और साबुनीकरण
Points to Remember
Ethanol C₂H₅OH (−OH, alcohol), neutral to litmus; ethanoic acid CH₃COOH (−COOH), turns blue litmus red.
Ethanol + Na → sodium ethoxide + hydrogen.
Ethanol + oxidising agent → ethanoic acid (orange dichromate turns green).
Ethanol + concentrated H₂SO₄ at 443 K → ethene + water.
Ethanoic acid + carbonate or bicarbonate → salt + water + carbon dioxide (brisk effervescence).
Acid + alcohol with concentrated H₂SO₄ → ester (fruity smell) + water: esterification.
Ester + NaOH → soap or sodium salt + alcohol: saponification.
Vinegar is 5–8% ethanoic acid; glacial acetic acid is pure and freezes at 16.6 °C.
⚠ Exam Tip 1: To separate the acid from the alcohol, use sodium hydrogencarbonate (the acid fizzes, the alcohol does not); the sodium test fails because both release hydrogen.
⚠ Exam Tip 2: Match the condition with the product: oxidation gives the acid, 443 K with concentrated H₂SO₄ gives ethene, and acid plus alcohol with H₂SO₄ gives the ester.