Article 194 · Chemistry
Class 10 chemistry is four chapters and about sixty reactions, and the board paper tests them in three ways: write the equation, name the type, and say what is observed. Students who know the reactions as a list fail the third question; students who know them as patterns answer all three. This page is every important reaction from the four chapters, balanced, with its condition and the observation the examiner wants, grouped by type so the pattern shows. The twenty asked most often are marked with a star. For the method of balancing, see how to balance chemical equations; for how to make the list stick, see the end of this page.
Chapter 1: Chemical reactions and equations
Combination reactions (two or more reactants, one product)
| Reaction |
Condition and observation |
| ★ CaO + H₂O → Ca(OH)₂ + heat |
Quicklime with water: the mixture hisses and gets very hot (exothermic); slaked lime is used to whitewash walls |
| ★ Ca(OH)₂ + CO₂ → CaCO₃ + H₂O |
Slaked lime on a whitewashed wall takes in CO₂ from the air over two to three days and forms a shiny calcium carbonate layer; also the lime-water test for CO₂ (turns milky) |
| 2Mg + O₂ → 2MgO |
Magnesium ribbon burns with a dazzling white flame, leaving white ash |
| C + O₂ → CO₂ |
Burning of coal, exothermic |
| 2H₂ + O₂ → 2H₂O |
Formation of water |
Decomposition reactions (one reactant, two or more products)
| Reaction |
Condition and observation |
| ★ 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃ |
Heat. Green ferrous sulphate crystals lose water, then turn reddish-brown (ferric oxide); smell of burning sulphur |
| ★ CaCO₃ → CaO + CO₂ |
Heat (thermal decomposition). Limestone to quicklime, used in cement |
| ★ 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ |
Heat. White lead nitrate gives yellow lead oxide and brown fumes of nitrogen dioxide |
| ★ 2H₂O → 2H₂ + O₂ |
Electricity (electrolysis). Hydrogen collects at the cathode in twice the volume of oxygen at the anode |
| ★ 2AgCl → 2Ag + Cl₂ |
Sunlight (photolysis). White silver chloride turns grey; the basis of black-and-white photography |
| 2AgBr → 2Ag + Br₂ |
Sunlight; the same, with silver bromide |
| 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ |
Heat; baking soda in baking (the CO₂ makes cake rise) |
Displacement reactions (a more reactive element replaces a less reactive one)
| Reaction |
Condition and observation |
| ★ Fe + CuSO₄ → FeSO₄ + Cu |
Iron nails in copper sulphate: the nails turn brown (copper deposits) and the blue solution turns light green |
| Zn + CuSO₄ → ZnSO₄ + Cu |
Blue solution turns colourless; copper deposits |
| Pb + CuCl₂ → PbCl₂ + Cu |
Lead displaces copper |
| Zn + 2HCl → ZnCl₂ + H₂ |
Also an acid-metal reaction; hydrogen gas pops with a burning splint |
Double displacement reactions (exchange of ions)
| Reaction |
Condition and observation |
| ★ Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl |
A white precipitate of barium sulphate forms at once (precipitation reaction) |
| NaOH + HCl → NaCl + H₂O |
Neutralisation, also double displacement |
| AgNO₃ + NaCl → AgCl + NaNO₃ |
White precipitate of silver chloride |
Oxidation and reduction (redox)
| Reaction |
Condition and observation |
| ★ CuO + H₂ → Cu + H₂O |
Heat. Black copper oxide turns brown (copper); CuO is reduced, H₂ is oxidised |
| ★ 2Cu + O₂ → 2CuO |
Heat. Copper powder turns black |
| ZnO + C → Zn + CO |
Heat; carbon reduces the oxide |
| MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂ |
HCl is oxidised to chlorine; MnO₂ is reduced |
| 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O |
Rusting: iron, moist air; the reddish-brown coating (corrosion). Rancidity of fats is the other everyday oxidation, slowed by antioxidants and nitrogen packing |
Chapter 2: Acids, bases and salts
Reactions of acids
| Reaction |
Condition and observation |
| ★ Zn + 2HCl → ZnCl₂ + H₂ (also 2HCl dilute with Mg, Fe, Al) |
Acid + metal → salt + hydrogen; the gas burns with a pop |
| ★ Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ |
Acid + carbonate → salt + water + CO₂; brisk effervescence; the gas turns lime water milky |
| ★ NaHCO₃ + HCl → NaCl + H₂O + CO₂ |
Acid + hydrogencarbonate, the same |
| ★ NaOH + HCl → NaCl + H₂O |
Acid + base → salt + water (neutralisation); the mixture warms |
| ★ CuO + 2HCl → CuCl₂ + H₂O |
Acid + metal oxide → salt + water; the black powder dissolves to a blue-green solution (metal oxides are basic) |
| CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ |
The same with marble chips |
| ★ Ca(OH)₂ + CO₂ → CaCO₃ + H₂O, then CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂ |
Lime water turns milky, then clear again when excess CO₂ is passed (soluble calcium hydrogencarbonate) |
Reactions of bases
| Reaction |
Condition and observation |
| ★ 2NaOH + Zn → Na₂ZnO₂ + H₂ |
Base + metal → salt (sodium zincate) + hydrogen |
| ★ Ca(OH)₂ + CO₂ → CaCO₃ + H₂O |
Base + non-metal oxide → salt + water (non-metal oxides are acidic) |
| 2NaOH + CO₂ → Na₂CO₃ + H₂O |
The same with sodium hydroxide |
Salts and their preparation
| Reaction |
Condition and observation |
| ★ 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ |
Electricity through brine (the chlor-alkali process): chlorine at the anode, hydrogen at the cathode, sodium hydroxide in solution |
| ★ Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O |
Chlorine on dry slaked lime gives bleaching powder (used for bleaching cotton, disinfecting water) |
| ★ NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃ |
Baking soda (sodium hydrogencarbonate) from brine, ammonia and CO₂ |
| ★ 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂, then Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O |
Heat, then recrystallisation: washing soda, used for glass, soap, paper and removing hardness |
| ★ CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O |
Plaster of Paris with water sets to hard gypsum within half an hour (casts, moulds) |
| CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O |
Gypsum heated to 373 K gives plaster of Paris; above that, dead burnt plaster |
| CuSO₄·5H₂O → CuSO₄ + 5H₂O |
Heat: blue crystals turn white (water of crystallisation lost); add water and the blue returns |
Metals with oxygen, water and acids
| Reaction |
Condition and observation |
| ★ 4Na + O₂ → 2Na₂O (then Na₂O + H₂O → 2NaOH) |
Sodium burns vigorously; stored under kerosene |
| 2Mg + O₂ → 2MgO; 4Al + 3O₂ → 2Al₂O₃; 2Cu + O₂ → 2CuO |
Mg burns with a white flame; Al and Cu form a protective oxide layer on heating |
| ★ 2Na + 2H₂O → 2NaOH + H₂ + heat (also K) |
Violent, the hydrogen catches fire |
| ★ Ca + 2H₂O → Ca(OH)₂ + H₂ |
Less violent; calcium floats because hydrogen bubbles stick to it |
| Mg + 2H₂O → Mg(OH)₂ + H₂ |
With hot water; Mg also floats |
| ★ 3Fe + 4H₂O (steam) → Fe₃O₄ + 4H₂ (also Al, Zn with steam) |
Metals of middle reactivity react only with steam |
| Fe + H₂SO₄ (dilute) → FeSO₄ + H₂; Mg + 2HCl → MgCl₂ + H₂ |
Hydrogen; copper does not react with dilute acids |
| Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O and Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O |
Aluminium oxide is amphoteric (reacts with acids and bases); zinc oxide too |
Reactivity and extraction
| Reaction |
Condition and observation |
| ★ Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat |
The thermite reaction: so much heat that the iron is molten; used to weld railway tracks |
| ★ 2ZnS + 3O₂ → 2ZnO + 2SO₂ |
Roasting: a sulphide ore heated in excess air |
| ★ ZnCO₃ → ZnO + CO₂ |
Calcination: a carbonate ore heated in limited air |
| ★ ZnO + C → Zn + CO |
Reduction of the oxide with carbon (metals of middle reactivity) |
| 2HgO → 2Hg + O₂ (heat); 2Cu₂O + Cu₂S → 6Cu + SO₂ |
Low-reactivity metals: heating the oxide alone is enough |
| 2Al₂O₃ → 4Al + 3O₂ (electrolysis, molten) |
High-reactivity metals are extracted by electrolysis (background in the rationalised syllabus) |
| 2NaCl → 2Na + Cl₂ (electrolysis, molten) |
Sodium at the cathode, chlorine at the anode |
Non-metals
| Reaction |
Condition and observation |
| S + O₂ → SO₂, then SO₂ + H₂O → H₂SO₃ |
Sulphur burns with a blue flame; the oxide dissolves to an acid that turns blue litmus red (non-metal oxides are acidic) |
| C + O₂ → CO₂; CO₂ + H₂O → H₂CO₃ |
The same with carbon |
Chapter 4: Carbon and its compounds
| Reaction |
Condition and observation |
| ★ CH₄ + 2O₂ → CO₂ + 2H₂O + heat (combustion) |
Saturated hydrocarbons burn with a clean blue flame; unsaturated with a sooty yellow flame |
| CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat |
Ethanol burns cleanly, a fuel |
| ★ CH₃CH₂OH + 2[O] → CH₃COOH + H₂O |
Alkaline KMnO₄ or acidified K₂Cr₂O₇, heat: oxidation of ethanol to ethanoic acid; the purple permanganate colour disappears |
| ★ CH₂=CH₂ + H₂ → CH₃–CH₃ |
Nickel or palladium catalyst: addition (hydrogenation); vegetable oil to ghee |
| ★ CH₄ + Cl₂ → CH₃Cl + HCl |
Sunlight: substitution, continues to CCl₄ |
| ★ 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂ |
Ethanol with sodium: hydrogen (burns with a pop) and sodium ethoxide |
| ★ CH₃CH₂OH → CH₂=CH₂ + H₂O |
Concentrated H₂SO₄, 443 K: dehydration to ethene |
| ★ CH₃COOH + NaOH → CH₃COONa + H₂O |
Neutralisation: sodium ethanoate |
| ★ 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂ (also with NaHCO₃) |
Brisk effervescence; the test that distinguishes a carboxylic acid from an alcohol |
| ★ CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O |
Concentrated H₂SO₄, warm: esterification; a sweet-smelling ester (ethyl ethanoate) |
| CH₃COOCH₂CH₃ + NaOH → CH₃COONa + CH₃CH₂OH |
Saponification: the ester with an alkali gives the salt of the acid and the alcohol; soap is made this way from fats |
| CH₂=CH₂ + Br₂ (aq) → CH₂Br–CH₂Br |
Bromine water decolourised: the test for unsaturation |
And from biology, the one asked in chemistry questions too: 6CO₂ + 12H₂O → (sunlight, chlorophyll) → C₆H₁₂O₆ + 6O₂ + 6H₂O, photosynthesis.
The twenty asked most, as a checklist
Ferrous sulphate heated; calcium carbonate heated; lead nitrate heated; silver chloride in sunlight; water electrolysed; iron in copper sulphate; quicklime with water; the lime-water test both ways; acid with metal, with a carbonate, with a base, with a metal oxide; base with zinc; the chlor-alkali process; bleaching powder; baking soda and washing soda; plaster of Paris; sodium and calcium with water; iron with steam; the thermite reaction; roasting and calcination of zinc; ethanol oxidised; ethanol with sodium; ethanol dehydrated; esterification; ethanoic acid with sodium carbonate. If you can write all twenty from blank paper with conditions, the chemistry questions of the paper are mostly done.
How to learn sixty reactions in two weeks
Not one by one. Each table above is a pattern: every decomposition is "one thing, energy, pieces"; every acid reaction ends in a salt plus hydrogen, water, or water and CO₂; every carbon reaction is one of four types. Learn the pattern first, then the examples, then test from blank paper: write every equation of one chapter from memory, mark it, rewrite only the missed ones, and repeat on day 3, day 7 and day 14. The same method, with the reasons it works, is in how to memorise maths formulas, and the chemistry version is in active recall for chemistry. In our Class 10 classes every reaction is written by the student on the whiteboard with its condition, and the chapter's list is tested from blank paper at the start of the next class; a child who "cannot remember reactions" usually can, within a month of that.
A team of 20+ women educators with master's degrees in chemistry and the sciences, teaching 1-on-1 online since 2018, in English, Hindi or Punjabi, to students in India, the Gulf, the UK and the US. The first 30-minute class is free; details on the CBSE Class 9 and 10 science page.
Questions parents ask
1Which chemical reactions are most important for the Class 10 board exam?
The twenty starred in the tables: the decomposition of ferrous sulphate, calcium carbonate, lead nitrate and silver chloride; iron with copper sulphate; the lime-water test; the reactions of acids with metals, carbonates and bases; the chlor-alkali process; bleaching powder, baking soda, washing soda and plaster of Paris; sodium and calcium with water; the thermite reaction; roasting and calcination of zinc ores; and the ethanol and ethanoic acid reactions. They are asked as "write the equation", "name the type" or "what is observed" almost every year.
2How do I remember all the chemical reactions of Class 10?
By type and by pattern, not one by one. The decomposition reactions all follow "one compound, heat or light or electricity, two or more products"; the acid reactions all end in salt plus hydrogen, salt plus water or salt plus water plus carbon dioxide; the carbon-compound reactions are four types with one example each. Learn the pattern, then test from blank paper: write all the equations of one chapter from memory, check, rewrite the missed ones, and repeat on day 3, 7 and 14.
3Do I have to write the conditions and the observations?
Yes, for full marks. The condition (heat, sunlight, electricity, a catalyst, concentrated acid at a temperature) goes above or beside the arrow, and when a question says "what is observed", the colour change, the gas, the precipitate or the heat is the mark: ferrous sulphate crystals turn from green to brown and a smell of burning sulphur; iron nails in copper sulphate turn brown and the blue solution fades to green.
4Is this list for the rationalised CBSE syllabus?
Yes. It follows the current CBSE Class 10 Science syllabus for the four chemistry chapters. Where NCERT dropped a topic in the rationalisation (such as the detail of the extraction of highly reactive metals and the refining of copper by electrolysis), the reaction is marked as background rather than core; check the year's syllabus document before the exam.
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