ICSE Class 8 Chemistry Question Paper & Answers (Semester 2) - 2025

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ICSE Class 8 Chemistry | Full Mock Paper

Syllabus: Language of Chemistry, Chemical Reactions, Physical & Chemical Changes

⏱️ Time: 2 Hours 📝 Max Marks: 80

Note: Click the "Show Answer" button to reveal the solution key for each question.

SECTION A (40 Marks) - Compulsory

Question 1 (Objective Type)

(A) Choose the correct answer: [10 Marks]

1. The valency of Iron in Ferric Chloride (FeCl₃) is: (a) 1 (b) 2 (c) 3 (d) 4

2. Which is a Chemical Change? (a) Melting ice (b) Rusting iron (c) Tearing paper (d) Glowing bulb

3. Symbol of Tungsten: (a) T (b) Tu (c) W (d) Tn

4. Reaction A + B → AB is: (a) Decomposition (b) Displacement (c) Synthesis (d) Double Decomposition

5. Formula of Ammonium Sulphate: (a) (NH₄)₂SO₄ (b) NH₄SO₄ (c) NH₃SO₄ (d) (NH₄)₃PO₄

6. In 2Mg + O₂ → 2MgO, the reactant is: (a) MgO (b) Mg (c) Mg and O₂ (d) None

7. Sublimation of Iodine is: (a) Physical Irreversible (b) Physical Reversible (c) Chemical (d) Undesirable

8. Valency of phosphate radical (PO₄): (a) -1 (b) -2 (c) -3 (d) +3

9. Catalyst that decreases reaction rate: (a) Positive (b) Promoter (c) Negative (d) Enzyme

10. Gas that burns with "pop" sound: (a) Oxygen (b) Hydrogen (c) CO₂ (d) Nitrogen

Answer Key: 1. (c) 3
2. (b) Rusting of iron
3. (c) W
4. (c) Synthesis (Combination)
5. (a) (NH₄)₂SO₄
6. (c) Mg and O₂
7. (b) Physical & Reversible change
8. (c) -3
9. (c) Negative catalyst
10. (b) Hydrogen

Question 2

(A) Match Column A with Column B: [5 Marks]

Column A	Column B
1. Curdling of Milk	(a) Variable Valency
2. Copper	(b) Decomposition Reaction
3. CaCO3 → CaO + CO2	(c) Chemical Change
4. Photosynthesis	(d) Displacement Reaction
5. Fe + CuSO4 → FeSO4 + Cu	(e) Endothermic Change

(B) Fill in the blanks: [5 Marks]

1. A chemical equation is balanced to satisfy the Law of ____________.

2. The Latin name for Potassium is ____________.

3. Burning of a candle involves both ____________ and ____________ changes.

4. Substances that take part in a chemical reaction are called ____________.

5. The valency of Carbon in CO₂ is ____________.

Answer Key (Match): 1 - (c) Chemical Change
2 - (a) Variable Valency
3 - (b) Decomposition Reaction
4 - (e) Endothermic Change
5 - (d) Displacement Reaction

Answer Key (Fill in blanks): 1. Conservation of Mass
2. Kalium
3. Physical, Chemical
4. Reactants
5. 4 (Tetravalency)

Question 3

(A) Write the chemical formula: [5 Marks]

1. Calcium Carbonate, 2. Zinc Nitrate, 3. Aluminium Oxide, 4. Sodium Bicarbonate, 5. Potassium Permanganate

(B) Balance the equations: [5 Marks]

1. Fe + H₂O → Fe₃O₄ + H₂

2. KClO₃ → KCl + O₂

3. N₂ + H₂ → NH₃

4. Al + O₂ → Al₂O₃

5. Zn + HCl → ZnCl₂ + H₂

Answer Key (Formulas): 1. CaCO₃
2. Zn(NO₃)₂
3. Al₂O₃
4. NaHCO₃
5. KMnO₄

Answer Key (Balancing): 1. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
2. 2KClO₃ → 2KCl + 3O₂
3. N₂ + 3H₂ → 2NH₃
4. 4Al + 3O₂ → 2Al₂O₃
5. Zn + 2HCl → ZnCl₂ + H₂

Question 4

(A) True or False: [5 Marks]

1. Rusting increases the weight of the iron object.

2. Formula for water is HO₂.

3. Neutralization is a reaction between acid and base.

4. Calcium exhibits variable valency.

5. Evolution of gas is a characteristic of chemical reactions.

(B) Name the following: [5 Marks]

1. Solid settled at bottom in a liquid reaction.

2. Number of atoms in one molecule of element.

3. Change where energy is evolved.

4. Radical present in Nitric Acid.

5. Short hand representation of an element.

Answer Key (True/False): 1. True
2. False (H₂O)
3. True
4. False
5. True

Answer Key (Naming): 1. Precipitate
2. Atomicity
3. Exothermic Change
4. Nitrate (NO₃^-1)
5. Symbol

SECTION B (40 Marks) - Subjective

Question 5 [10 Marks]

1. Differentiate between Physical and Chemical Change (3 points). [3]
2. Define 'Radical'. Give one example of monovalent basic and divalent acid radical. [3]
3. Calculate Molecular Mass (H=1, O=16, C=12, Ca=40): a) H₂O, b) CaCO₃ [4]

Model Answer:

1. Differences:
- Physical: Temporary, Reversible, No new substance formed.
- Chemical: Permanent, Irreversible, New substance formed.

2. Radical: An atom or group of atoms behaving as a single unit with a charge.
- Monovalent Basic: Ammonium (NH₄⁺) or Sodium (Na⁺)
- Divalent Acid: Sulphate (SO₄^2-) or Carbonate (CO₃^2-)

3. Molecular Mass:
a) H₂O = (2×1) + 16 = 18 amu
b) CaCO₃ = 40 + 12 + (3×16) = 40 + 12 + 48 = 100 amu

Question 6 [10 Marks]

1. What is Variable Valency? Name two metals showing it. [4]
2. Write balanced equations for: [6]
a) Phosphorus + Oxygen → Phosphorus Pentoxide
b) Sodium + Water → Sodium Hydroxide + Hydrogen
c) Calcium Hydroxide + Carbon Dioxide → Calcium Carbonate + Water

Model Answer:

1. Variable Valency: Some elements exhibit more than one valency.
Examples: Iron (Fe²⁺, Fe³⁺) and Copper (Cu¹⁺, Cu²⁺).

2. Equations:
a) P₄ + 5O₂ → 2P₂O₅ (or 4P + 5O₂ → 2P₂O₅)
b) 2Na + 2H₂O → 2NaOH + H₂
c) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Question 7 [10 Marks]

1. Classify as Physical or Chemical: [4]
a) Digestion b) Magnetization c) Ripening fruit d) Boiling water
2. Define with example: [6]
a) Decomposition b) Double Displacement c) Synthesis

Model Answer:

1. Classification:
a) Chemical b) Physical c) Chemical d) Physical

2. Definitions:
a) Decomposition: One compound splits into two or more simpler substances. (e.g., CaCO₃ → CaO + CO₂)
b) Double Displacement: Two compounds exchange radicals to form new compounds. (e.g., NaCl + AgNO₃ → AgCl + NaNO₃)
c) Synthesis: Two elements combine to form a compound. (e.g., C + O₂ → CO₂)

Question 8 [10 Marks]

1. Explain terms: a) Effervescence b) Precipitate [4]
2. Significance of Chemical Formula. [3]
3. Why is respiration a chemical change? [3]

Model Answer:

1. Terms:
a) Effervescence: The rapid formation of gas bubbles in a liquid during a chemical reaction (fizzing).
b) Precipitate: An insoluble solid formed that settles down during a reaction between two solutions.

2. Significance of Formula:
It tells us the elements present, the number of atoms of each element, and the molecular mass of the compound.

3. Respiration:
It is a chemical change because glucose breaks down (oxidizes) to form new substances (CO₂ and water) and energy is released. It is irreversible.

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