📊 Lessons & Marks Weightage (As per ICSE Board Pattern)

📌 Detailed Breakdown of Study of Compounds:

📘 Subject: Chemistry
🎓 Class: X (ICSE)
📊 Maximum Marks: 80
⏰ Time Allowed: 2 Hours

📋 General Instructions:

1. ✍️ Answers to this Paper must be written on the paper provided separately.

2. ⏳ You will not be allowed to write during the first 15 minutes. This time is to be spent in reading the question paper.

3. 🕐 The time given at the head of this Paper is the time allowed for writing the answers.

4. ✅ Attempt all questions from Section A and any four questions from Section B.

5. 📝 All working, including rough work, must be clearly shown and must be done on the same sheet as the rest of the answer.

6. ⚠️ Omission of essential working will result in loss of marks.

7. 🎯 The intended marks for questions or parts of questions are given in brackets [ ].

8. 📐 Scientific calculators and log tables are not allowed.

📕 SECTION A (40 Marks)

(Attempt all questions from this Section.)

❓ Question 1 [15 Marks]

Choose the correct answers to the questions from the given options. (Do not copy the questions, write the correct answers only.)

(i) ⚡ Which of the following is a non-electrolyte?
(a) NaCl solution
(b) Dilute H₂SO₄
(c) Glucose solution
(d) CuSO₄ solution

✅ Answer: (c) Glucose solution
📖 Explanation: Glucose does not dissociate into ions in solution, hence it is a non-electrolyte.

(ii) ⚡ During electrolysis of acidified water, the gas evolved at the cathode is:
(a) Oxygen
(b) Hydrogen
(c) Chlorine
(d) Nitrogen

✅ Answer: (b) Hydrogen
📖 Explanation: At cathode (negative electrode), H⁺ ions gain electrons to form hydrogen gas.

(iii) ⚡ The electrolyte used in the electroplating of silver is:
(a) Silver nitrate
(b) Silver chloride
(c) Silver sulphate
(d) Silver cyanide (potassium argentocyanide)

✅ Answer: (d) Silver cyanide (potassium argentocyanide)
📖 Explanation: Potassium argentocyanide is used as electrolyte for silver plating.

(iv) 💨 Which gas is evolved when dilute HCl is added to sodium carbonate?
(a) Hydrogen
(b) Oxygen
(c) Carbon dioxide
(d) Chlorine

✅ Answer: (c) Carbon dioxide
📖 Explanation: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑

(v) 💨 The gas which turns moist red litmus paper blue is:
(a) HCl
(b) NH₃
(c) CO₂
(d) SO₂

✅ Answer: (b) NH₃
📖 Explanation: Ammonia is basic in nature and turns red litmus blue.

(vi) 💨 Which of the following is used as a drying agent for ammonia gas?
(a) Conc. H₂SO₄
(b) P₂O₅
(c) Quick lime (CaO)
(d) Anhydrous CaCl₂

✅ Answer: (c) Quick lime (CaO)
📖 Explanation: Ammonia is basic, so it cannot be dried with acidic drying agents like H₂SO₄ or P₂O₅. CaO is basic and suitable.

(vii) 💨 The catalyst used in Ostwald’s process for manufacture of nitric acid is:
(a) Iron
(b) Platinum gauze
(c) Vanadium pentoxide
(d) Manganese dioxide

✅ Answer: (b) Platinum gauze
📖 Explanation: Ostwald’s process uses platinum gauze as catalyst for oxidation of ammonia to nitric oxide.

(viii) 💨 In the contact process for manufacture of sulphuric acid, the catalyst used is:
(a) Platinum
(b) Vanadium pentoxide (V₂O₅)
(c) Iron
(d) Nickel

✅ Answer: (b) Vanadium pentoxide (V₂O₅)
📖 Explanation: V₂O₅ is used as catalyst in contact process.

(ix) 💨 Which of the following is a property of hydrogen chloride gas?
(a) It is coloured
(b) It is lighter than air
(c) It is heavier than air
(d) It has a sweet smell

✅ Answer: (c) It is heavier than air
📖 Explanation: HCl gas is about 1.28 times heavier than air.

(x) 💨 The compound formed when ammonia reacts with excess chlorine is:
(a) N₂
(b) NCl₃
(c) NH₄Cl
(d) NO

✅ Answer: (b) NCl₃
📖 Explanation: 2NH₃ + 3Cl₂ → N₂ + 6HCl (excess NH₃); NH₃ + 3Cl₂ → NCl₃ + 3HCl (excess Cl₂)

(xi) 🔬 In the laboratory preparation of HCl gas, the drying agent used is:
(a) Conc. H₂SO₄
(b) Quick lime
(c) NaOH
(d) KOH

✅ Answer: (a) Conc. H₂SO₄
📖 Explanation: Conc. H₂SO₄ is used to dry HCl gas as it does not react with it.

(xii) 🔬 The flame colour observed when a nichrome wire dipped in HCl is introduced into a non-luminous flame is:
(a) Golden yellow
(b) Brick red
(c) Apple green
(d) Blue

✅ Answer: (d) Blue
📖 Explanation: HCl gives a blue flame colouration in the flame test.

(xiii) 🔬 Which of the following is used to test for chloride ions?
(a) BaCl₂ solution
(b) AgNO₃ solution
(c) NaOH solution
(d) FeSO₄ solution

✅ Answer: (b) AgNO₃ solution
📖 Explanation: AgNO₃ gives a white precipitate of AgCl with chloride ions.

(xiv) 🔬 The gas evolved when dilute HCl is added to iron(II) sulphide is:
(a) H₂S
(b) SO₂
(c) Cl₂
(d) O₂

✅ Answer: (a) H₂S
📖 Explanation: FeS + 2HCl → FeCl₂ + H₂S↑ (rotten egg smell)

(xv) 🔬 In the test for nitrate ions, the brown ring complex formed is:
(a) [Fe(H₂O)₅NO]SO₄
(b) [Fe(H₂O)₅NO]²⁺
(c) [Fe(NO)]SO₄
(d) [Fe(H₂O)₆]²⁺

✅ Answer: (b) [Fe(H₂O)₅NO]²⁺
📖 Explanation: Brown ring complex is nitroso ferrous sulphate, [Fe(H₂O)₅NO]SO₄.

❓ Question 2 [12 Marks]

(Solve the following)

(i) ⚡ State three differences between electrolytic conduction and metallic conduction. [4]

✅ Answer:

(ii) 💨 Explain the laboratory preparation of ammonia gas with a balanced chemical equation and a labelled diagram. [4]

✅ Answer:

📝 Laboratory Preparation of Ammonia:

Chemicals: Ammonium chloride (NH₄Cl) and slaked lime [Ca(OH)₂]

Equation:
2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2H₂O + 2NH₃↑

Diagram:

        ┌─────────────┐
        │  NH₄Cl +    │
        │  Ca(OH)₂    │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │   Hard      │
        │   Glass     │
        │   Test Tube │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │  Delivery   │
        │   Tube      │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │  NH₃ Gas    │
        │  Collected  │
        │  by Downward│
        │  Displacement│
        └─────────────┘

Method: The mixture is heated in a hard glass test tube. Ammonia gas is collected by downward displacement of air (since it is lighter than air).

(iii) 💨 Write balanced chemical equations for:
(a) Ammonia reacts with excess chlorine
(b) Nitric acid reacts with copper
(c) Sulphuric acid reacts with sodium hydroxide
(d) Hydrogen chloride reacts with ammonia [4]

✅ Answer:

(a) NH₃ + 3Cl₂ (excess) → NCl₃ + 3HCl

(b) 3Cu + 8HNO₃ (dilute) → 3Cu(NO₃)₂ + 2NO + 4H₂O

(c) H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

(d) HCl + NH₃ → NH₄Cl (white fumes of ammonium chloride)

❓ Question 3 [12 Marks]

(Solve the following)

(i) ⚡ Explain the electrolysis of acidified water with a labelled diagram. [4]

✅ Answer:

📝 Electrolysis of Acidified Water:

Electrolyte: Acidified water (H₂SO₄ added to distilled water)

Electrodes: Platinum electrodes

Diagram:

        ┌─────────────────────────┐
        │     +           −       │
        │     │           │       │
        │  ┌──▼──┐     ┌──▼──┐    │
        │  │Pt   │     │Pt   │    │
        │  │Anode│     │Cathode│   │
        │  └──┬──┘     └──┬──┘    │
        │     │           │       │
        │  ═══╪═══════════╪═══    │
        │     │  Acidified │       │
        │     │   Water    │       │
        │     └────────────┘       │
        └─────────────────────────┘

Reactions:

• At Cathode (−): 4H⁺ + 4e⁻ → 2H₂↑ (Hydrogen gas)

• At Anode (+): 2H₂O → O₂ + 4H⁺ + 4e⁻ (Oxygen gas)

Overall: 2H₂O → 2H₂ + O₂

Ratio: Hydrogen : Oxygen = 2 : 1 (by volume)

(ii) 💨 Describe the contact process for manufacture of sulphuric acid with equations. [4]

✅ Answer:

📝 Contact Process for H₂SO₄:

Step 1: Burning of sulphur in air
S + O₂ → SO₂

Step 2: Catalytic oxidation of SO₂ to SO₃
2SO₂ + O₂ ⇌ 2SO₃ (Catalyst: V₂O₅, Temperature: 450°C, Pressure: 2 atm)

Step 3: Absorption of SO₃ in conc. H₂SO₄
SO₃ + H₂SO₄ → H₂S₂O₇ (Oleum)

Step 4: Dilution of oleum
H₂S₂O₇ + H₂O → 2H₂SO₄

Conditions:

• Catalyst: Vanadium pentoxide (V₂O₅)

• Temperature: 450°C

• Pressure: 2 atmospheres

(iii) 🔬 Give one chemical test to distinguish between:
(a) HCl gas and NH₃ gas
(b) Dilute HCl and dilute HNO₃
(c) FeSO₄ and FeCl₃
(d) SO₂ and CO₂ [4]

✅ Answer:

(a) HCl vs NH₃: HCl turns moist blue litmus red; NH₃ turns moist red litmus blue.

(b) Dilute HCl vs Dilute HNO₃: Add AgNO₃ solution. HCl gives white precipitate of AgCl; HNO₃ gives no precipitate.

(c) FeSO₄ vs FeCl₃: Add NaOH solution. FeSO₄ gives dirty green precipitate of Fe(OH)₂; FeCl₃ gives reddish-brown precipitate of Fe(OH)₃.

(d) SO₂ vs CO₂: Pass through acidified K₂Cr₂O₇ solution. SO₂ turns it green; CO₂ has no effect.

📗 SECTION B (40 Marks)

(Attempt any four questions from this Section.)

❓ Question 4 [10 Marks]

(i) ⚡ Define the following terms:
(a) Electrolyte
(b) Non-electrolyte
(c) Electrolysis [3]

✅ Answer:

(a) Electrolyte: A substance which in aqueous solution or molten state conducts electricity and undergoes chemical decomposition.

(b) Non-electrolyte: A substance which does not conduct electricity in aqueous solution or molten state.

(c) Electrolysis: The process of decomposition of an electrolyte by the passage of electric current.

(ii) 💨 Write short notes on:
(a) Aqua regia
(b) Brown ring test [3]

✅ Answer:

(a) Aqua Regia: A mixture of 3 parts concentrated HCl and 1 part concentrated HNO₃. It is a strong oxidizing agent and dissolves noble metals like gold and platinum.

(b) Brown Ring Test: Test for nitrate ions. To the solution, add FeSO₄ solution and then slowly add conc. H₂SO₄ along the walls of the test tube. A brown ring of [Fe(H₂O)₅NO]SO₄ forms at the junction.

(iii) 🔬 A gas ‘X’ is evolved when dilute HCl is added to a compound ‘Y’. The gas ‘X’ turns lime water milky. Identify X and Y. Write the balanced equation. [4]

✅ Answer:

Gas X: Carbon dioxide (CO₂)
Compound Y: Calcium carbonate (CaCO₃) or any carbonate/bicarbonate

Equation:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

Test: CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O (lime water turns milky)

❓ Question 5 [10 Marks]

(i) ⚡ Explain why:
(a) Copper cannot be used as anode in electrolysis of CuSO₄ solution with platinum electrodes.
(b) A solution of HCl in water conducts electricity but a solution of HCl in toluene does not. [3]

✅ Answer:

(a) If copper is used as anode, it will dissolve into the solution instead of being deposited. Platinum is inert and does not react.

(b) HCl in water dissociates into H⁺ and Cl⁻ ions which conduct electricity. HCl in toluene does not dissociate into ions, hence does not conduct.

(ii) 💨 How is nitric acid manufactured by Ostwald’s process? Write all equations. [3]

✅ Answer:

📝 Ostwald’s Process:

Step 1: Catalytic oxidation of ammonia
4NH₃ + 5O₂ → 4NO + 6H₂O (Catalyst: Pt gauze, Temp: 800°C)

Step 2: Oxidation of NO to NO₂
2NO + O₂ → 2NO₂

Step 3: Absorption of NO₂ in water
3NO₂ + H₂O → 2HNO₃ + NO

(iii) 🔬 Draw a labelled diagram for the laboratory preparation of hydrogen chloride gas and write the equation. [4]

✅ Answer:

📝 Laboratory Preparation of HCl Gas:

Chemicals: Sodium chloride (NaCl) and concentrated H₂SO₄

Equation:
NaCl + H₂SO₄ → NaHSO₄ + HCl↑ (at 150°C)
NaHSO₄ + NaCl → Na₂SO₄ + HCl↑ (at 200°C)

Diagram:

        ┌─────────────┐
        │  NaCl +     │
        │  Conc.      │
        │  H₂SO₄      │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │   Round     │
        │   Bottom    │
        │   Flask     │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │  Delivery   │
        │   Tube      │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │  Conc.      │
        │  H₂SO₄      │
        │  (Drying)   │
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │  HCl Gas    │
        │  Collected  │
        │  by Upward  │
        │  Displacement│
        └─────────────┘

Method: HCl gas is collected by upward displacement of air (since it is heavier than air).

❓ Question 6 [10 Marks]

(i) ⚡ What is electroplating? Explain the electroplating of iron with silver. [3]

✅ Answer:

Electroplating: The process of depositing a thin layer of one metal on another metal using electrolysis.

Silver Plating on Iron:

• Cathode (−): Iron article

• Anode (+): Pure silver rod

• Electrolyte: Potassium argentocyanide [KAg(CN)₂]

Reactions:

• At Cathode: Ag⁺ + e⁻ → Ag (deposited on iron)

• At Anode: Ag → Ag⁺ + e⁻ (dissolves from silver rod)

(ii) 💨 Give reasons:
(a) Ammonia is not dried by conc. H₂SO₄.
(b) Nitric acid turns yellow on standing.
(c) HCl gas gives white fumes with ammonia. [3]

✅ Answer:

(a) Ammonia is basic and reacts with conc. H₂SO₄ to form ammonium sulphate. Hence, it cannot be dried.

(b) Nitric acid decomposes in presence of light to form NO₂ which dissolves in it, giving a yellow colour.

(c) HCl reacts with NH₃ to form white fumes of ammonium chloride (NH₄Cl).

(iii) 🔬 Complete the following reactions:
(a) NH₄Cl + Ca(OH)₂ →
(b) Cu + 4HNO₃ (conc.) →
(c) SO₂ + H₂O →
(d) AgNO₃ + HCl → [4]

✅ Answer:

(a) 2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2H₂O + 2NH₃↑

(b) Cu + 4HNO₃ (conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O

(c) SO₂ + H₂O → H₂SO₃

(d) AgNO₃ + HCl → AgCl↓ + HNO₃ (white precipitate)

❓ Question 7 [10 Marks]

(i) ⚡ State Faraday’s laws of electrolysis. [3]

✅ Answer:

First Law: The mass of substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed.
m ∝ Q = It
m = ZIt (where Z is electrochemical equivalent)

Second Law: When the same quantity of electricity is passed through different electrolytes, the masses of substances deposited or liberated are proportional to their chemical equivalent weights.
m₁/m₂ = E₁/E₂

(ii) 💨 What is the action of heat on:
(a) Ammonium chloride
(b) Copper nitrate
(c) Lead nitrate [3]

✅ Answer:

(a) NH₄Cl → NH₃ + HCl (decomposes on heating)

(b) 2Cu(NO₃)₂ → 2CuO + 4NO₂ + O₂ (copper nitrate decomposes)

(c) 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ (lead nitrate decomposes)

(iii) 🔬 A white precipitate is obtained when BaCl₂ solution is added to a solution of compound ‘X’. The precipitate is insoluble in dilute HCl. Identify ‘X’ and write the equation. [4]

✅ Answer:

Compound X: Sodium sulphate (Na₂SO₄) or any sulphate

Precipitate: Barium sulphate (BaSO₄) — white, insoluble in dilute HCl

Equation:
Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

Test: BaSO₄ is insoluble in dilute HCl, confirming sulphate ions.

❓ Question 8 [10 Marks]

(i) ⚡ Explain the terms:
(a) Electrochemical equivalent
(b) Current efficiency [3]

✅ Answer:

(a) Electrochemical Equivalent (Z): The mass of substance deposited or liberated by 1 coulomb of electricity. Z = E/F (where E is equivalent weight, F is Faraday constant).

(b) Current Efficiency: The ratio of actual mass deposited to the theoretical mass deposited, expressed as percentage.

(ii) 💨 Write the chemical equations for:
(a) Catalytic oxidation of ammonia
(b) Reaction of nitric acid with sulphur
(c) Reaction of sulphuric acid with copper [3]

✅ Answer:

(a) 4NH₃ + 5O₂ → 4NO + 6H₂O (Catalyst: Pt, Temp: 800°C)

(b) S + 6HNO₃ (conc.) → H₂SO₄ + 6NO₂ + 2H₂O

(c) Cu + 2H₂SO₄ (conc.) → CuSO₄ + SO₂ + 2H₂O

(iii) 🔬 Draw a labelled diagram of the apparatus used to test for chloride ions and explain the test. [4]

✅ Answer:

📝 Test for Chloride Ions:

Diagram:

        ┌─────────────────────────┐
        │   Test Tube             │
        │   ┌───────────────┐     │
        │   │  Solution +   │     │
        │   │  AgNO₃        │     │
        │   │  (White ppt)  │     │
        │   └───────────────┘     │
        └─────────────────────────┘

Method:

1. Take the given solution in a test tube.

2. Add a few drops of dilute HNO₃.

3. Add AgNO₃ solution.

4. A white precipitate of AgCl is formed.

5. The precipitate is soluble in ammonium hydroxide but insoluble in dilute HNO₃.

Equation:
NaCl + AgNO₃ → AgCl↓ + NaNO₃

❓ Question 9 [10 Marks]

(i) ⚡ Calculate the mass of copper deposited when a current of 2 A is passed through CuSO₄ solution for 30 minutes. (E.C.E. of Cu = 0.000329 g/C) [3]

✅ Answer:

Given: I = 2 A, t = 30 min = 1800 s, Z = 0.000329 g/C

m = ZIt
m = 0.000329 × 2 × 1800
m = 0.000329 × 3600
m = 1.1844 g

✔️ Mass of copper deposited = 1.1844 g

(ii) 💨 Explain the term “oleum” and write its formula. [3]

✅ Answer:

Oleum: It is pyrosulphuric acid (H₂S₂O₇), formed when SO₃ is dissolved in concentrated H₂SO₄.

Formula: H₂S₂O₇

Formation: SO₃ + H₂SO₄ → H₂S₂O₇

(iii) 🔬 A compound ‘X’ on heating with NaOH gives a gas ‘Y’ which turns red litmus blue. Identify X and Y. Write the equation and name the test. [4]

✅ Answer:

Compound X: Ammonium salt (e.g., NH₄Cl)
Gas Y: Ammonia (NH₃)

Equation:
NH₄Cl + NaOH → NaCl + H₂O + NH₃↑

Test: Ammonia turns red litmus blue. It also gives white fumes with HCl.

❓ Question 10 [10 Marks]

(i) ⚡ What is the role of cryolite in the electrolytic extraction of aluminium? [3]

✅ Answer:

Role of Cryolite (Na₃AlF₆):

• It lowers the melting point of alumina (Al₂O₃) from about 2050°C to about 950°C.

• It increases the conductivity of the electrolyte.

• It dissolves alumina and makes it a good conductor.

(ii) 💨 Describe the test for nitrate ions with equations. [3]

✅ Answer:

📝 Brown Ring Test for Nitrates:

1. Take the solution in a test tube.

2. Add freshly prepared FeSO₄ solution.

3. Slowly add conc. H₂SO₄ along the walls of the test tube.

4. A brown ring forms at the junction of the two liquids.

Equation:
2NO₃⁻ + 4H₂SO₄ + 6FeSO₄ → 3Fe₂(SO₄)₃ + 2NO + 4H₂O + 2SO₄²⁻
[Fe(H₂O)₆]SO₄ + NO → [Fe(H₂O)₅NO]SO₄ + H₂O (Brown ring)

(iii) 🔬 A gas ‘X’ has a pungent smell and turns acidified K₂Cr₂O₇ green. Identify ‘X’ and write two tests to confirm it. [4]

✅ Answer:

Gas X: Sulphur dioxide (SO₂)

Tests:

1. Acidified K₂Cr₂O₇ test: SO₂ turns orange K₂Cr₂O₇ green due to reduction.
   K₂Cr₂O₇ + H₂SO₄ + SO₂ → K₂SO₄ + Cr₂(SO₄)₃ + H₂O
   (Orange → Green)

2. Lime water test: SO₂ turns lime water milky due to formation of CaSO₃.
   SO₂ + Ca(OH)₂ → CaSO₃↓ + H₂O

🎓 END OF QUESTION PAPER

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