This ICSE Class 10 Chemistry Model Paper 3 with Answers is designed for students of Dhingra Classes Nashik, with structured questions, chemical equations, practical identification tests, reasoning-based questions and diagram-based exercises.

The paper covers all the requested syllabus areas: Electrolysis, Study of Compounds (all four parts), and Practical Chemistry. Each question is immediately followed by its answer to help students practise, check their understanding and revise important concepts.

📊 Lessons and marks weightage

The chapter-wise allocations are suggested practice targets for this custom paper, not official ICSE chapter-wise weightages. The attached PDF was not available in the current message, so the paper below uses an 80-mark, two-section practice structure. Please provide the PDF if its exact pattern must be reproduced.

📝 SECTION A — 40 Marks

Attempt all questions in this section. Every question is followed by its answer for revision.

Question 1: Multiple-choice questions [15 marks]

Choose the correct option. Each question carries 1 mark.

(i) During electrolysis, the movement of anions towards the anode is associated with:

(a) Reduction (b) Oxidation (c) Neutralisation (d) Hydrolysis

Answer: (b) Oxidation. Anions lose electrons at the anode in an electrolytic cell.

(ii) Which substance is most suitable for drying ammonia gas?

(a) Concentrated sulphuric acid (b) Anhydrous calcium chloride (c) Quicklime (d) Phosphorus pentoxide

Answer: (c) Quicklime,

$\mathrm{C}\mathrm{a}\mathrm{O}$

CaO, because it removes moisture without reacting significantly with ammonia under the drying conditions.

(iii) Which gas is liberated at the anode during the electrolysis of concentrated aqueous sodium chloride using inert electrodes?

(a) Hydrogen (b) Oxygen (c) Chlorine (d) Nitrogen

Answer: (c) Chlorine, under suitable concentrated brine electrolysis conditions.

(iv) Which nitrogen oxide is formed when ammonia is catalytically oxidised in the Ostwald process?

(a)  ${\mathrm{N}}_2\mathrm{O}$

 (b) $\mathrm{N}\mathrm{O}$

 (c) $\mathrm{N}{\mathrm{O}}_{\mathrm{2 }}$ only as the primary product

${\mathrm{(d)\; N}}_2{\mathrm{O}}_5$

Answer: (b) Nitric oxide,

$\mathrm{N}\mathrm{O}$

(v) Which property makes hydrogen chloride unsuitable for collection over water?

(a) It is colourless (b) It is highly soluble in water (c) It is a covalent compound (d) It has a pungent odour

Answer: (b) It is highly soluble in water.

(vi) What is the role of a platinum catalyst in the Ostwald process?

(a) It absorbs nitrogen dioxide (b) It increases the rate of ammonia oxidation (c) It neutralises nitric acid (d) It removes water from ammonia

Answer: (b) It increases the rate of ammonia oxidation.

(vii) Which acid is manufactured industrially by the Contact process?

(a) Hydrochloric acid (b) Nitric acid (c) Sulphuric acid (d) Carbonic acid

Answer: (c) Sulphuric acid.

(viii) What is the oxidation state of nitrogen in nitric acid,

$\mathrm{H}\mathrm{N}{\mathrm{O}}_3$

(a) +3 (b) +4 (c) +5 (d) −3

Answer: (c) +5.

(ix) Which observation indicates that a copper(II) salt may be present when aqueous sodium hydroxide is added?

(a) A green gas is evolved (b) A pale blue precipitate forms (c) A silver mirror forms (d) A yellow flame appears

Answer: (b) A pale blue precipitate of copper(II) hydroxide forms.

(x) Which of the following is a suitable electrolyte for copper purification?

(a) Pure distilled water (b) Acidified copper(II) sulphate solution (c) Concentrated sodium hydroxide only (d) Molten sodium chloride

Answer: (b) Acidified copper(II) sulphate solution.

(xi) Which reagent is commonly used to test for carbon dioxide?

(a) Limewater (b) Silver nitrate solution (c) Acidified potassium dichromate (d) Aqueous ammonia only

Answer: (a) Limewater. Carbon dioxide turns limewater milky due to calcium carbonate formation.

(xii) Which of the following gases can act as a reducing agent by removing oxygen from hot metal oxides?

(a) Ammonia (b) Helium (c) Neon (d) Argon

Answer: (a) Ammonia can reduce certain hot metal oxides, such as copper(II) oxide.

(xiii) Which apparatus is most appropriate for delivering a controlled volume of a liquid reagent during a titration?

(a) Beaker (b) Burette (c) Watch glass (d) Evaporating dish

Answer: (b) Burette.

(xiv) When an aqueous salt solution gives a gelatinous white precipitate with aqueous sodium hydroxide that dissolves in excess, which ion could be present?

(a) Aluminium(III) (b) Iron(III) (c) Copper(II) (d) Calcium(II), in the usual qualitative test

Answer: (a) Aluminium(III), because aluminium hydroxide dissolves in excess sodium hydroxide.

(xv) Why is an electrolyte required in an electrolytic cell?

(a) It prevents ion movement (b) It provides mobile ions to carry current through the liquid (c) It stops all chemical reactions (d) It converts electrons into neutrons

Answer: (b) It provides mobile ions to carry current through the liquid.

Question 2: Short-answer questions [12 marks]

(i) Explain the difference between electrolysis of a molten ionic compound and an aqueous solution of the same compound. [3]

Answer:

• In a molten compound, the ions from the ionic compound are the principal mobile ionic species.

• In an aqueous solution, water may also provide ions or compete in electrode reactions.

• Consequently, the products formed in aqueous electrolysis can differ from those obtained from the molten compound.

(ii) Give balanced equations for the following reactions. [3]

(a) Sulphur trioxide reacts with sodium hydroxide.

(b) Nitrogen dioxide reacts with water and oxygen to form nitric acid.

(c) Ammonium nitrate decomposes on heating to form nitrous oxide and water.

Answer:

(a)

(b)

(c)$$\mathrm{N}{\mathrm{H}}_4\mathrm{N}{\mathrm{O}}_3\stackrel{\mathrm{\Delta }}{\to }{\mathrm{N}}_2\mathrm{O}+2{\mathrm{H}}_2\mathrm{O}$$

(iii) Give reasons for the following. [3]

(a) Copper is used as the cathode during electrolytic refining of copper.

(b) Ammonia forms white fumes when it comes into contact with hydrogen chloride gas.

(c) Sulphur dioxide is considered a reducing agent in certain chemical reactions.

Answer:

(a) Copper ions gain electrons at the cathode and are deposited as pure copper.

(b) Ammonia and hydrogen chloride react to form fine particles of ammonium chloride.

(c) Sulphur dioxide can be oxidised to sulphate or sulphuric acid while reducing another substance.

(iv) State one confirmatory observation for each of the following ions. [3]

(a) Iron(II) (b) Iron(III) (c) Ammonium

Answer:

(a) Iron(II): A dirty-green precipitate of iron(II) hydroxide forms with aqueous sodium hydroxide.

(b) Iron(III): A reddish-brown precipitate of iron(III) hydroxide forms with aqueous sodium hydroxide.

(c) Ammonium: On warming with aqueous sodium hydroxide, ammonia is evolved and turns moist red litmus paper blue.

Question 3: Diagram-based and structured questions [13 marks]

(i) Study the electrolytic refining diagram and answer the questions. [4]

(a) Identify the anode and cathode. [1]

(b) Write the half-equation for the reaction at the cathode. [1]

(c) What happens to insoluble impurities present in the impure copper anode? [1]

(d) State the function of the electrolyte. [1]

Answer:

(a) Impure copper is the anode; pure copper is the cathode.

(b)$$\mathrm{C}{\mathrm{u}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{C}\mathrm{u}$$

(c) Insoluble impurities may settle below the anode as anode sludge.

(d) The electrolyte conducts ionic current and supplies copper ions for deposition.

(ii) Consider the following reactions involving nitric acid. [4]

(a) Why does copper react with concentrated nitric acid to produce brown fumes? [1]

(b) Name the brown gas. [1]

(c) Write the balanced chemical equation for the reaction. [1]

(d) State the role of nitric acid in this reaction. [1]

Answer:

(a) Concentrated nitric acid oxidises copper and is reduced to a nitrogen oxide.

(b) Nitrogen dioxide,

$\mathrm{N}{\mathrm{O}}_2$

(c)$$\mathrm{C}\mathrm{u}+4\mathrm{H}\mathrm{N}{\mathrm{O}}_3(\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}\mathrm{.})\to \mathrm{C}\mathrm{u}(\mathrm{N}{\mathrm{O}}_3{)}_2+2\mathrm{N}{\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}$$

(iii) A student receives a sample of an unknown salt. Describe how the student could test for carbonate ions and state the expected result. [5]

Answer:

1. Place a small amount of the sample in a test tube.

2. Add dilute hydrochloric acid carefully.

3. If carbonate ions are present, effervescence occurs as carbon dioxide is evolved.

4. Pass the gas through fresh limewater.

5. The limewater turns milky due to the formation of calcium carbonate.

Ionic equation:

Limewater test:

Attempt any four questions. Each question carries 10 marks. For revision purposes, answers are included for all five questions.

Question 4: Electrolysis and electrochemical applications [10 marks]

(i) Explain the electrolysis of molten aluminium oxide in the extraction of aluminium. [4]

Answer:

• Aluminium oxide is dissolved in molten cryolite to lower the operating temperature and improve electrical conductivity.

• Aluminium ions migrate towards the cathode and gain electrons.

• Oxide ions migrate towards the anode and discharge to form oxygen.

• The carbon anodes are gradually consumed because oxygen reacts with the hot carbon.

Cathode:

Anode:

(ii) Draw a labelled diagram of an electrolytic cell used to electroplate an iron key with silver. [3]

Answer:

The three essential labels are:

• Anode (+): Pure silver.

• Cathode (−): Clean iron key.

• Electrolyte: A suitable solution containing silver ions.

At the cathode:

(iii) State three factors that affect the quality of an electroplated coating. [3]

Answer:

1. Cleanliness of the article’s surface.

2. Current density and duration of electrolysis.

3. Composition and concentration of the electrolyte, together with suitable operating conditions.

Question 5: Hydrogen Chloride and laboratory chemistry [10 marks]

(i) A laboratory worker prepares hydrogen chloride gas from sodium chloride. Explain why concentrated sulphuric acid is suitable for this preparation. [3]

Answer:

• Concentrated sulphuric acid is a relatively non-volatile acid under the reaction conditions.

• It displaces hydrogen chloride from sodium chloride.

• Hydrogen chloride is evolved as a gas and can be collected by downward displacement of air.

(a) Hydrogen chloride reacts with silver nitrate solution. [1]

(b) Hydrochloric acid reacts with calcium carbonate. [1]

(c) Hydrogen chloride reacts with magnesium. [1]

Answer:

(a)

(b)

(c)

(iii) A gas turns moist blue litmus red and forms dense white fumes when a glass rod dipped in ammonia solution is brought near it. Identify the gas and explain both observations. [4]

Answer:

The gas is hydrogen chloride.

• It dissolves in moisture and forms an acidic solution, turning moist blue litmus red.

• It reacts with ammonia to form solid ammonium chloride particles, which appear as dense white fumes.

The litmus test must be carried out with appropriate precautions because hydrogen chloride gas is irritating and corrosive.

Question 6: Ammonia and Nitric Acid [10 marks]

(i) Describe the principal steps in the industrial manufacture of nitric acid by the Ostwald process. [4]

Answer:

1. Ammonia is mixed with air and passed over a platinum-based catalyst at high temperature to form nitric oxide.

2. Nitric oxide is oxidised to nitrogen dioxide.

(ii) Explain why ammonia acts as a Lewis base. [2]

Answer:

The nitrogen atom in ammonia has a lone pair of electrons. It can donate this lone pair to an electron-pair acceptor to form a coordinate bond. Hence, ammonia acts as a Lewis base.

(iii) Write balanced equations for the reactions of nitric acid with the following substances. [2]

(a) Sodium hydroxide (b) Calcium carbonate

Answer:

(a)$$\mathrm{H}\mathrm{N}{\mathrm{O}}_3+\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\to \mathrm{N}\mathrm{a}\mathrm{N}{\mathrm{O}}_3+{\mathrm{H}}_2\mathrm{O}$$

(b)$$\mathrm{C}\mathrm{a}\mathrm{C}{\mathrm{O}}_3+2\mathrm{H}\mathrm{N}{\mathrm{O}}_3\to \mathrm{C}\mathrm{a}(\mathrm{N}{\mathrm{O}}_3{)}_2+{\mathrm{H}}_2\mathrm{O}+\mathrm{C}{\mathrm{O}}_2\uparrow$$

Answer:

1. Work in a properly ventilated laboratory or fume cupboard when handling irritating gases or concentrated acids.

2. Wear appropriate eye protection, gloves and a laboratory coat, and avoid direct contact or inhalation.

Question 7: Sulphuric Acid and the Contact Process [10 marks]

(i) Draw a flow diagram showing the main stages in the Contact process. [4]

Answer:

(ii) Why is sulphur trioxide not normally absorbed directly in water on an industrial scale? [2]

Answer:

The reaction is highly exothermic and produces a fine mist of sulphuric acid that is difficult to condense and collect efficiently. Instead, sulphur trioxide is absorbed in concentrated sulphuric acid to form oleum, which is then diluted carefully.

(iii) Explain the action of concentrated sulphuric acid on hydrated copper(II) sulphate crystals. [2]

Answer:

Concentrated sulphuric acid removes water of crystallisation from hydrated copper(II) sulphate, changing the blue crystals into a pale or white anhydrous form.

(iv) State two uses of sulphuric acid. [2]

Answer:

1. Manufacture of fertilisers such as ammonium sulphate and superphosphate.

2. Manufacture of chemicals, including detergents, dyes and other industrial products.

Question 8: Practical Chemistry and analytical reasoning [10 marks]

(i) A student is given three unknown solutions. The following observations are recorded. Identify the likely ions. [3]

(a) A white precipitate forms with aqueous sodium hydroxide and dissolves in excess. [1]

(b) A light-blue precipitate forms with aqueous sodium hydroxide. [1]

(c) On warming with aqueous sodium hydroxide, a gas turns moist red litmus paper blue. [1]

Answer:

(a) Aluminium ions,

$\mathrm{A}{\mathrm{l}}^{3+}$

or zinc ions,

$\mathrm{Z}{\mathrm{n}}^{2+ }$may give a white precipitate soluble in excess sodium hydroxide. A further confirmatory test is needed to distinguish them.

(b) Copper(II) ions,

$\mathrm{C}{\mathrm{u}}^{2+}$

(c) Ammonium ions,

$\mathrm{N}{\mathrm{H}}_4^{+}$

are indicated by the evolution of ammonia.

(ii) Describe the confirmatory test for sulphate ions and give the ionic equation. [3]

Answer:

• Acidify a fresh portion of the solution with dilute hydrochloric acid.

• Add barium chloride solution.

• A white precipitate that remains insoluble in dilute hydrochloric acid indicates sulphate ions.

Answer:

1. Inform the teacher or laboratory supervisor immediately and keep others away from the spill.

2. Follow the laboratory’s approved spill procedure, using appropriate protective equipment and a suitable neutralising or clean-up method under supervision.

(iv) Why should a precipitate be washed with distilled water during gravimetric or qualitative analysis? [2]

Answer:

Washing removes soluble impurities and residual reagents adhering to the precipitate. Distilled water is used to avoid introducing additional dissolved ions that could contaminate the sample.

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