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CBSE · Class 10 · Science

Chemical Reactions and Equations

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
The reaction 4Al + 3O2 → 2Al2O3 is an example of:
  1. a decomposition reaction
  2. a combination reaction
  3. a double displacement reaction
  4. a displacement reaction
2.
Which of these chemical equations is correctly balanced?
  1. 2AgCl → 2Ag + 2Cl2
  2. 2AgCl → 3Ag + Cl2
  3. 2AgCl → 2Ag + Cl2
  4. 3AgCl → 2Ag + Cl2
3.
A reaction in which heat is given out is called:
  1. decomposition
  2. endothermic
  3. displacement
  4. exothermic
4.
In the reaction ZnO + C → Zn + CO, the substance oxidised is:
  1. C
  2. Zn
  3. ZnO
  4. CO
5.
Solutions of iron(II) sulphate (FeSO4) and sodium hydroxide (NaOH) are mixed. The precipitate formed is:
  1. NaOH
  2. Fe(OH)2
  3. Na2SO4
  4. FeSO4
6.
Which of these is an exothermic process?
  1. Respiration
  2. Decomposition of silver chloride in sunlight
  3. Electrolysis of water
  4. Heating of lead nitrate
7.
Which gas is given off when zinc granules react with dilute sulphuric acid?
  1. sulphur dioxide
  2. nitrogen dioxide
  3. hydrogen
  4. carbon dioxide
8.
Assertion (A): In the balanced equation for Ca(OH)2 + HCl → CaCl2 + H2O, the coefficient of H2O is 2.
Reason (R): A balanced equation has the same number of atoms of each element on both sides.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
Section B — Short answer8 × 2 = 16 marks
9.
Balance the equation: Cl2 + KBr → KCl + Br2
10.
How many atoms of oxygen are there in 4C12H22O11?
11.
In the reaction Fe2O3 + 2Al → Al2O3 + 2Fe, name the oxidising agent and the reducing agent.
12.
Why should a magnesium ribbon be cleaned with sandpaper before burning it in air?
13.
Write the balanced chemical equation for: barium chloride + sulphuric acid → barium sulphate + hydrochloric acid
14.
When 175 g of zinc carbonate is heated strongly, 113.4 g of zinc oxide is left and carbon dioxide escapes. What mass of carbon dioxide is given off? Which law did you use?
15.
Find the molecular mass of ZnSO4. (Atomic masses: O = 16 u, S = 32 u, Zn = 65 u)
16.
Name the gas given off when calcium carbonate is heated strongly. How would you test for it?
Section C — Word problems4 × 4 = 16 marks
17.
A shiny brown element X turns black when heated in air. Name X and the black compound, and write the balanced equation.
18.
For the reaction CaO + H2O → Ca(OH)2, find the masses of the other substances when 252 g of CaO reacts completely. (Atomic masses: H = 1 u, O = 16 u, Ca = 40 u)
19.
Write the balanced chemical equation for each, and name the type of reaction:
(a) sulphuric acid + sodium hydroxide → sodium sulphate + water
(b) hydrogen + oxygen → water
20.
Solutions of barium chloride and dilute sulphuric acid are mixed. (a) What do you see? (b) Write the balanced equation. (c) Name the type of reaction.
AmbifulWorksheets
Practice that never repeats
CBSE · Class 10 · Science

Answer key

Chemical Reactions and Equations · AW-10S-CRE-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(b) a combination reactiontwo or more substances combine to form one product
2(c) 2AgCl → 2Ag + Cl2count each kind of atom on both sides
3(d) exothermic—
4(a) CC gains oxygen or loses hydrogen (oxidised); ZnO loses oxygen or gains hydrogen (reduced)
5(b) Fe(OH)2Fe(OH)2 is insoluble in water
6(a) Respirationit gives out heat
7(c) hydrogenit burns with a pop sound when a burning splinter is brought near
8(a) Both A and R are true, and R is the correct explanation of A.A is true: balanced: Ca(OH)2 + 2HCl → CaCl2 + 2H2O. R is true and explains A.
9Cl2 + 2KBr → 2KCl + Br2make the atoms of each element equal on both sides
104411 in one unit × 4
11Oxidising agent: Fe2O3; reducing agent: AlFe2O3 is reduced (it oxidises the other); Al is oxidised
12To remove the layer of magnesium oxide on its surface, so that the magnesium burns readily.—
13BaCl2 + H2SO4 → BaSO4 + 2HClformulas first, then balance: BaCl2 + H2SO4 → BaSO4 + HCl
1461.6 g; the law of conservation of mass175 − 113.4
15161 u1 × 65 + 1 × 32 + 4 × 16
16Carbon dioxide: it turns lime water milky—
17X is copper and the black compound is copper(II) oxide: 2Cu + O2 → 2CuO.—
1881 g of H2O; 333 g of Ca(OH)2molar masses CaO = 56, H2O = 18, Ca(OH)2 = 74; CaO: 252 g is 4.5 mol
19(a) H2SO4 + 2NaOH → Na2SO4 + 2H2O — double displacement; (b) 2H2 + O2 → 2H2O — combination—
20(a) A white precipitate of BaSO4. (b) BaCl2 + H2SO4 → BaSO4 + 2HCl. (c) Double displacement (precipitation).—