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Vidaara.orgClass 10 · Chemistry
CodeC10-CHEM-1-CW
Chapter Assignment — Chemical Reactions and Equations
Chapter: Chemical Reactions and Equations
Topic: All Topics
Maximum Marks: 40
Time: 90 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • This is a full-length worksheet covering the whole chapter — every topic is included.
  • All questions are compulsory.
  • Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
  • Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions 6 × 1 = 6 marks
1.
A balanced equation satisfies the law of conservation of:
  • A.energy
  • B.mass
  • C.volume
  • D.charge only
2.
CaO + H2O → Ca(OH)2 is a:
  • A.decomposition reaction
  • B.combination reaction
  • C.displacement reaction
  • D.precipitation reaction
3.
The yellow precipitate formed from Pb(NO3)2 and KI is:
  • A.KNO3
  • B.PbI2
  • C.PbO
  • D.KI
4.
Loss of oxygen by a substance is called:
  • A.oxidation
  • B.reduction
  • C.corrosion
  • D.rancidity
5.
Rusting of iron needs:
  • A.only air
  • B.only water
  • C.both air and water
  • D.neither
6.
Antioxidants are added to oily foods to prevent:
  • A.rusting
  • B.rancidity
  • C.neutralisation
  • D.combustion
Section B — Short Answer (2 marks) 4 × 2 = 8 marks
7.
Balance: Fe2O3 + Al → Al2O3 + Fe and name the type of reaction.
8.
Define a precipitation reaction and give one balanced example.
9.
In CuO + H2 → Cu + H2O, identify the oxidising and reducing agents.
10.
State two methods to prevent rancidity in packaged food.
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
11.
Balance and add state symbols: zinc + dilute sulphuric acid, and name the gas evolved.
12.
Explain, with a balanced equation, what happens when an iron nail is dipped in copper sulphate solution.
Section D — Long Answer (5 marks) 2 × 5 = 10 marks
13.
Define oxidation and reduction in terms of oxygen and hydrogen. Using the reaction CuO + H2 → Cu + H2O, explain why it is a redox reaction and identify the agents. Then explain how corrosion and rancidity are both consequences of oxidation.
14.
Name and define the four main types of chemical reactions, giving one balanced equation for each, and state for each whether it is usually exothermic or endothermic.

Answer Key

Section A — Multiple Choice Questions
  1. (B) mass
  2. (B) combination reaction
  3. (B) PbI2
  4. (B) reduction
  5. (C) both air and water
  6. (B) rancidity
Section B — Short Answer (2 marks)
  1. Fe₂O₃ + 2Al → Al₂O₃ + 2Fe; it is a displacement (and redox) reaction — the thermite reaction.
  2. A reaction in which an insoluble solid (precipitate) forms when two solutions mix, e.g. Na₂SO₄ + BaCl₂ → BaSO₄ (precipitate) + 2NaCl.
  3. CuO is the oxidising agent (it is reduced); H₂ is the reducing agent (it is oxidised).
  4. Any two of: add antioxidants, use air-tight packaging, refrigerate, or flush the packet with nitrogen to exclude oxygen.
Section C — Short Answer (3 marks)
  1. Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g); the gas evolved is hydrogen, which burns with a pop sound.
  2. Iron displaces copper because it is more reactive: Fe + CuSO₄ → FeSO₄ + Cu. The blue colour fades to pale green and a brown copper deposit forms on the nail — a displacement reaction.
Section D — Long Answer (5 marks)
  1. Oxidation is gain of oxygen or loss of hydrogen; reduction is loss of oxygen or gain of hydrogen. In CuO + H₂ → Cu + H₂O, CuO loses oxygen (reduced, oxidising agent) and H₂ gains oxygen (oxidised, reducing agent); since both occur together it is a redox reaction. Corrosion is the oxidation of a metal by air and moisture — iron is oxidised to rust (hydrated iron(III) oxide). Rancidity is the oxidation of fats and oils in food by atmospheric oxygen, giving a bad smell and taste. Both are everyday examples of substances being oxidised by oxygen.
  2. Combination (A + B → AB): CaO + H₂O → Ca(OH)₂, exothermic. Decomposition (AB → A + B): CaCO₃ → CaO + CO₂, endothermic. Displacement (A + BC → AC + B): Fe + CuSO₄ → FeSO₄ + Cu, usually exothermic. Double displacement (AB + CD → AD + CB): Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl (precipitation); neutralisation HCl + NaOH → NaCl + H₂O is exothermic.
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