ICSE Class 10 Chemistry Board Exam Question Paper 2012 with Solutions

ICSE Class 10 Chemistry Board Exam Question Paper with Solutions

SECTION-I (40 Marks)

Attempt all questions from this Section

Question 1.

(a) Name the gas in each of the following : [5 Marks]
(i) The gas evolved on reaction of Aluminium with boiling concentrated caustic alkali solution.
(ii) The gas produced when excess ammonia reacts with chlorine.
(iii) A gas which turns acidified potassium dichromate clear green.
(iv) The gas produced when copper reacts with concentrated nitric acid.
(v) The gas produced on reaction of dilute sulphuric acid with a metallic sulphide.

Answer:
(i) Hydrogen
(ii) Nitrogen
(iii) Sulphur dioxide
(iv) Nitrogen dioxide
(v) Hydrogen sulphide

Teacher's Note:
a) Remember the specific gaseous products formed during reactions of metals with alkalis and acids, as well as oxidizing and reducing reactions.
b) Do not confuse nitrogen dioxide (reddish brown) with nitric oxide (colourless gas that turns brown in air).

(b) State one observation for each of the following : [5 Marks]
(i) Excess ammonium hydroxide solution is added to lead nitrate solution.
(ii) Bromine vapours are passed into a solution of ethyne in carbon tetrachloride.
(iii) A zinc granule is added to copper sulphate solution.
(iv) Zinc nitrate crystals are strongly heated.
(v) Sodium hydroxide solution is added to ferric chloride solution at little and then in excess.

Answer:
(i) Insoluble chalky white precipitate of lead hydroxide is obtained.
(ii) Reddish brown colour of bromine water disappears.
(iii) The blue colour of copper sulphate solution disappears.
(iv) Reddish brown fumes of nitrogen dioxide a colourless gas that rekindles a glowing splint are released. In the test tube, a ppt is left which is yellow when hot and white when cold.
(v) Insoluble reddish brown ppt obtained.

Teacher's Note:
a) For precipitation reactions, always specify the exact colour and solubility of the precipitate formed.
b) Thermal decomposition of metal nitrates typically yields metal oxides, nitrogen dioxide, and oxygen gas.

(c) Some word/words are missing in the following statements. You are required to rewrite the statements in the correct form using the appropriate word/words : [5 Marks]
(i) Ethyl alcohol is dehydrated by sulphuric acid at a temperature of about 170 degree C.
(ii) Aqua regia contains one part by volume of nitric acid and three parts by volume of hydrochloric acid.
(iii) Magnesium nitride reacts with water to liberate ammonia.
(iv) Cations migrate to cathode during electrolysis.
(v) Magnesium reacts with nitric acid to liberate hydrogen gas.

Answer:
(i) Ethyl alcohol is dehydrated by concentrated sulphuric acid at a temperature of about 170 degree C.
(ii) Aqua regia contains one part by volume of concentrated nitric acid and three parts by volume of concentrated hydrochloric acid.
(iii) Magnesium nitride reacts with boiling water to liberate ammonia.
(iv) Cations migrate to cathode during electrolysis.
(v) Magnesium reacts with very dilute nitric acid to liberate hydrogen gas.

Teacher's Note:
a) Pay close attention to qualifiers like 'concentrated', 'boiling', and 'very dilute' as they change reaction outcomes significantly.
b) Ensure that missing terms in incomplete factual statements are filled with exact scientific terminology.

(d) Choose the correct answer from the options given below : [5 Marks]
(i) An element in period-3 whose electron affinity is zero.
(A) Neon
(B) Sulphur
(C) Sodium
(D) Argon
(ii) An alkaline earth metal.
(A) Potassium
(B) Calcium
(C) Lead
(D) Copper
(iii) The vapour density of carbon dioxide [C = 12, O = 16]
(A) 32
(B) 16
(C) 44
(D) 22
(iv) Identify the weak electrolyte from the following :
(A) Sodium Chloride solution
(B) Dilute Hydrochloric acid
(C) Dilute Sulphuric acid
(D) Aqueous acetic acid
(v) Which of the following metallic oxides cannot be reduced by normal reducing agents ?
(A) Magnesium oxide
(B) Copper(II) oxide
(C) Zinc oxide
(D) Iron(III) oxide

Answer: (D)
(i) (D) Argon
(ii) (B) Calcium
(iii) (D) 22
(iv) (D) Aqueous acetic acid
(v) (A) Magnesium oxide

Teacher's Note:
a) Noble gases like argon have stable octets/duplets, giving them zero electron affinity.
b) Highly reactive metals like magnesium and sodium form stable oxides that cannot be reduced by carbon, carbon monoxide, or hydrogen.

(e) Match the following : [5 Marks]
Column A
1. Acid salt
2. Double salt
3. Ammonium hydroxide solution
4. Dilute hydrochloric acid
5. Carbon tetrachloride
Column B
A. Ferrous ammonium sulphate
B. Contains only ions
C. Sodium hydrogen sulphate
D. Contains only molecules
E. Contains ions and molecules

Answer:
1. Acid salt - C. Sodium hydrogen sulphate
2. Double salt - A. Ferrous ammonium sulphate
3. Ammonium hydroxide solution - E. Contains ions and molecules
4. Dilute hydrochloric acid - B. Contains only ions (Note: strong acids ionize almost completely, yielding mainly ions along with very few molecules of water, but classically matched to ions/molecules contextually; let us follow standard matching: 3-E, 4-B)
5. Carbon tetrachloride - D. Contains only molecules

Teacher's Note:
a) Acid salts contain replaceable hydrogen ions, whereas double salts are addition compounds that dissociate into simple ions in solution.
b) Covalent compounds like carbon tetrachloride exist purely as molecules in solution and do not conduct electricity.

(f) Give the structural formula for the following : [5 Marks]
(i) Methanoic acid
(ii) Ethanal
(iii) Ethyne
(iv) Acetone
(v) 2-methyl propane

Answer:
(i) Methanoic acid: H - C(=O) - O - H
(ii) Ethanal: H - C(H)(H) - C(=O) - H
(iii) Ethyne: H - C triple bond C - H
(iv) Acetone: CH₃ - C(=O) - CH₃
(v) 2-methyl propane: (CH₃)₃CH or central carbon bonded to three methyl groups and one hydrogen.

Teacher's Note:
a) Ensure all covalent bonds (single, double, or triple) are clearly represented in structural formulas.
b) Check the valency of carbon (four) for every single carbon atom in the drawn chain.

(g) Concentrated nitric acid oxidises phosphorus to phosphoric acid according to the following equation :
P + 5HNO₃ (conc.) → H₃PO₄ + H₂O + 5NO₂
If 9.3g of phosphorus was used in the reaction, calculate :
(i) Number of moles of phosphorus taken. [1 Mark]
(ii) The mass of phosphoric acid formed. [2 Marks]
(iii) The volume of nitrogen dioxide produced at STP. [2 Marks]
[H = 1, N = 14, P = 31, O = 16]

Answer:
(i) No. of moles of P = 9.3 / 31 = 0.3 moles.
(ii) From equation, 31 g of P produces 98 g of H₃PO₄ (since molar mass of H₃PO₄ = 3(1) + 31 + 4(16) = 98 g).
Therefore, 9.3 g of P produces = (98 / 31) * 9.3 = 29.4 g.
(iii) From equation, 31 g of P releases 5 * 22.4 litres of NO₂ at STP = 112 litres.
Therefore, 9.3 g of P releases = (112 / 31) * 9.3 = 33.6 litres.

Teacher's Note:
a) Always use stoichiometry from the balanced chemical equation to establish mass-mole-volume relationships.

b) Ensure molar masses are calculated correctly with appropriate units (g/mol or litres at STP).

(h) Give reasons for the following : [5 Marks]
(i) Iron is rendered passive with fuming nitric acid.
(ii) An aqueous solution of sodium chloride conducts electricity.
(iii) Ionisation potential of the element increases across a period.
(iv) Alkali metals are good reducing agents.
(v) Hydrogen chloride gas cannot be dried over quick lime.

Answer:
(i) Concentrated nitric acid being a strong oxidising agent oxidises iron, forming a thin layer that makes iron non-reactive or passive.
(ii) Aqueous solution of sodium chloride contains mobile ions like Na⁺, Cl^-, H⁺, OH^-, H₃O⁺ etc. so they conduct electricity.
(iii) Atomic size decreases and nuclear charge increases as we move from left to right in a period so energy required to remove one electron from the valence shell increases thus ionisation potential increases.
(iv) Alkali metals readily lose electrons and get oxidised. So they behave as good reducing agents.
(v) Hydrogen chloride is acidic whereas quick lime is basic. As they react with each other hence quick lime can not be used to dry hydrogen chloride.

Teacher's Note:
a) Use clear chemical principles such as ionization, passivation, and acid-base reactions to justify observations.
b) Periodic trends must be explained by linking atomic radius and nuclear charge effectively.

SECTION-II (40 Marks)

Answer any four questions from this section

Question 2.

(a) Some properties of sulphuric acid are listed below. Choose the role played by sulphuric acid as A, B, C or D which is responsible for the reactions (i) to (v). Some role/s may be repeated. [5 Marks]
A. Dilute acid.
B. Dehydrating agent.
C. Non-volatile acid
D. Oxidising agent
(i) CuSO₄.5H₂O → CuSO₄ + 5H₂O (Conc. H₂SO₄ above arrow)
(ii) S + H₂SO₄ (conc.) → 3SO₂ + 2H₂O
(iii) NaNO₃ + H₂SO₄ (conc.) → NaHSO₄ + HCl (less than 200 degree C)
(iv) MgO + H₂SO₄ → MgSO₄ + H₂O
(v) Zn + 2H₂SO₄ (conc.) → ZnSO₄ + SO₂ + 2H₂O

Answer:
(i) B - Dehydrating agent.
(ii) D - Oxidising agent.
(iii) C - Non-volatile acid.
(iv) A - Dilute acid.
(v) D - Oxidising agent.

Teacher's Note:
a) Identify the property of sulphuric acid based on whether it removes water, acts as an acid, or undergoes redox reactions.
b) High-temperature reactions involving displacement of volatile acids demonstrate its non-volatile nature.

(b) Give balanced equations for the following reactions : [5 Marks]
(i) Dilute nitric acid and Copper carbonate.
(ii) Concentrated hydrochloric acid and Potassium permanganate.
(iii) Ammonia and Oxygen in the presence of a catalyst.
(iv) Silver nitrate solution and sodium chloride solution.
(v) Zinc sulphide and Dilute sulphuric acid.

Answer:
(i) CuCO₃ + 2HNO₃ → Cu(NO₃)₂ + H₂O + CO₂
(ii) 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂
(iii) 4NH₃ + 5O₂ → (Pt / 800 degree C) → 4NO + 6H₂O
(iv) AgNO₃ + NaCl → AgCl + NaNO₃
(v) ZnS + H₂SO₄ → ZnSO₄ + H₂S

Teacher's Note:
a) Ensure all chemical equations are fully balanced with proper reactant and product states.
b) Mention reaction conditions like temperature and catalysts where specified.

Question 3.

(a) Select the correct answer from the list given in brackets : [5 Marks]
(i) An aqueous electrolyte consists of the ions mentioned in the list, the ion which could be discharged most readily during electrolysis. [Fe²⁺, Cu²⁺, Pb²⁺, H⁺]
(ii) The metallic electrode which does not take part in an electrolytic reaction. [Cu, Ag, Pt, Ni]
(iii) The ion which is discharged at the anode during the electrolysis of copper sulphate solutions using copper electrodes as anode and cathode. [Cu²⁺, OH^-, SO₄^2-, H⁺]
(iv) When dilute sodium chloride is electrolysed using graphite electrodes, the cation is discharged at the cathode most readily. [Na⁺, OH^-, H⁺, Cl^-]
(v) During silver plating of an article using potassium argentocyanide as an electrolyte, the anode material should be [Cu, Ag, Pt, Fe]

Answer:
(i) Cu²⁺
(ii) Pt
(iii) Nil (As copper anode dissolves to form copper ions, no ion is discharged at the anode)
(iv) H⁺
(v) Ag

Teacher's Note:
a) Understand the electrochemical series to determine which ions are preferentially discharged during electrolysis.
b) In electrorefining and electroplating, active metal anodes dissolve into solution rather than discharging anions.

(b) Match the properties and uses of alloys in List 1 with the appropriate answer from List 2. [5 Marks]
List 1
1. The alloy contains Cu and Zn, is hard, silvery and is used in decorative articles.
2. It is stronger than Aluminium, light and is used in making light tools.
3. It is lustrous, hard, corrosion resistant and used in surgical instruments.
4. Tin lowers the melting point of the alloy and is used for soldering purpose.
5. The alloy is hard, brittle, takes up polish and is used for making statues.
List 2
A. Duralumin
B. Brass
C. Bronze
D. Stainless steel
E. Solder

Answer:
1. The alloy contains Cu and Zn, is hard, silvery and is used in decorative articles. - B. Brass
2. It is stronger than Aluminium, light and is used in making light tools. - A. Duralumin
3. It is lustrous, hard, corrosion resistant and used in surgical instruments. - D. Stainless steel
4. Tin lowers the melting point of the alloy and is used for soldering purpose. - E. Solder
5. The alloy is hard, brittle, takes up polish and is used for making statues. - C. Bronze

Teacher's Note:
a) Memorize the composition, properties, and specific uses of major commercial alloys.
b) Duralumin contains aluminium, copper, magnesium, and manganese, making it lightweight and strong.

Question 4.

(a) Identify the anion present in the following compounds : [4 Marks]
(i) Compound X on heating with copper turnings and concentrated sulphuric acid liberates a reddish brown gas.
(ii) When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in excess of ammonium hydroxide solution.
(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which turns lime water milky, but the gas has no effect on acidified potassium dichromate solution.
(iv) Compound L on reacting with Barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or dilute nitric acid.

Answer:
(i) NO₃^- (Nitrate ion)
(ii) Cl^- (Chloride ion)
(iii) CO₃^2- (Carbonate ion)
(iv) SO₄^2- (Sulphate ion)

Teacher's Note:
a) Analytical chemistry questions rely on identifying specific gases or precipitates formed during qualitative tests.
b) Sulphate ions produce a white precipitate with barium chloride that is insoluble in mineral acids.

(b) State one chemical test between each of the following pairs : [3 Marks]
(i) Sodium carbonate and Sodium sulphite.
(ii) Ferrous nitrate and Lead nitrate.
(iii) Manganese dioxide and Copper(II) oxide.

Answer:
(i) Add dil. HCl or dil. H₂SO₄:
- Sodium carbonate: Colourless, odourless gas that turn lime water milky but has no effect on acidified potassium dichromate is released i.e., CO₂.
- Sodium sulphite: Colourless gas with smell of burning sulphur, turn lime water milky and also turn acidified potassium dichromate green is released i.e., SO₂ gas.
(ii) Add few drops of NaOH:
- Ferrous nitrate: Dirty green ppt of Ferrous hydroxide.
- Lead nitrate: Chalky white ppt of lead hydroxide.
(iii) Heat with conc. HCl:
- Manganese dioxide: Greenish yellow gas with irritating smell and acidic nature is released i.e., chlorine gas.
- Copper(II) oxide: No reaction.

Teacher's Note:
a) Distinguishing tests must highlight a distinct observable difference such as gas evolution, colour change, or precipitate formation.
b) Always name the reagent used and the specific observations for both compounds being compared.

(c) Draw an electron dot diagram to show the structure of hydronium ion. State the type of bonding present in it. [3 Marks]

Answer:

[Figure: Lewis structure of H₃O⁺ showing water molecule donating a lone pair of electrons to a hydrogen ion (H⁺), resulting in a coordinate covalent bond and overall positive charge.]

The type of bonding present in it is Co-ordinate bonding (dative bonding) and covalent bonding.

Teacher's Note:
a) The hydronium ion is formed when a water molecule uses its oxygen atom's lone pair to bond with a hydrogen ion (proton).
b) Clearly show both covalent bonds and the coordinate bond with an arrow pointing from the donor atom to the acceptor.

Question 5.

(a) (i) 67.2 litres of hydrogen combines with 44.8 litres of nitrogen to form ammonia under specific conditions as :
N₂(g) + 3H₂(g) → 2NH₃(g)
Calculate the volume of ammonia produced. What is the other substance, if any, that remains in the resultant mixture ? [2 Marks]
(ii) The mass of 5.6 dm³ of a certain gas at STP is 12.0 g. Calculate the relative molecular mass of the gas. [2 Marks]
(iii) Find the total percentage of Magnesium in magnesium nitrate crystals, Mg(NO₃)₂.6H₂O. [Mg = 24; N = 14; O = 16 and H = 1] [2 Marks]

Answer:
(i) According to Gay Lussac's Law of Combining Volumes:
N₂ + 3H₂ → 2NH₃
1 vol : 3 vol → 2 vol
If 1 vol. of N₂ gives 2 vol. of NH₃, then 44.8 l of N₂ gives (2/1) * 44.8 = 89.6 l.
(ii) Volume of the gas at STP = 5.6 dm³ = 5.6 l.
Mass of the gas = 12.0 g.
Volume at STP = (Mass / Mol. wt) * 22.4
5.6 = (12 / Mol. wt) * 22.4
Mol. wt. = (12 * 22.4) / 5.6 = 48 g.
(iii) Molar mass of Mg(NO₃)₂.6H₂O = 24 + 2(14 + 48) + 6(18) = 24 + 124 + 108 = 256 g.
% of Mg = (24 / 256) * 100 = 9.375%.

Teacher's Note:
a) Apply Avogadro's law and molar volume concepts correctly for gas stoichiometry problems.
b) For percentage composition, divide the total mass of the element by the total molecular mass of the compound and multiply by 100.

(b) Refer to the flow chart diagram below and give balanced equations with conditions, if any, for the following conversions A to D. [4 Marks]
[Figure: Flow chart showing Sodium Chloride reacting with A to give Hydrogen Chloride, which then forms Iron(II) Chloride via B, Ammonium Chloride via C, and Lead Chloride via D.]

Answer:
(A) NaCl + H₂SO₄ (conc.) → NaHSO₄ + HCl (Temperature less than 200 degree C)
(B) Fe + 2HCl (dil.) → FeCl₂ + H₂
(C) NH₃ + HCl → NH₄Cl
(D) Pb(NO₃)₂ + 2HCl → PbCl₂ + 2HNO₃

Teacher's Note:
a) Trace each arrow in chemical conversion flowcharts carefully to identify reactants and reaction conditions.
b) Ensure reactions for preparing metallic chlorides and ammonium salts are correctly balanced.

Question 6.

(a) Name the following metals : [3 Marks]
(i) A metal present in cryolite other than sodium.
(ii) A metal which is unaffected by dilute or concentrated acids.
(iii) A metal present in period 3, group 1 of the periodic table.

Answer:
(i) Aluminium
(ii) Gold
(iii) Sodium

Teacher's Note:
a) Cryolite has the chemical formula Na₃AlF₆, containing sodium, aluminium, and fluorine.
b) Noble metals like gold and platinum do not react with ordinary mineral acids.

(b) The following questions are relevant to the extraction of Aluminium : [3 Marks]
(i) State the reason for addition of caustic alkali to bauxite ore during purification of bauxite.
(ii) Give a balanced chemical equation for the above reaction.
(iii) Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.

Answer:
(i) To dissolve bauxite ore and obtain a solution of Sodium Aluminate.
(ii) Al₂O₃.2H₂O + 2NaOH → (Fusion) → 2NaAlO₂ + 3H₂O
(iii) Fluorspar (CaF₂). To reduce the high melting point of alumina and to make it a conducting medium.

Teacher's Note:
a) Baeyer's process uses sodium hydroxide to selectively dissolve aluminium oxide while leaving impurities behind.
b) Cryolite and fluorspar are added to pure alumina in the Hall-Héroult process to lower its melting point and improve conductivity.

(c) The following questions are based on the preparation of ammonia gas in the laboratory : [4 Marks]
(i) Explain why ammonium nitrate is not used in the preparation of ammonia.
(ii) Name the compound normally used as a drying agent during the process.
(iii) How is ammonia gas collected?
(iv) Explain why it is not collected over water.

Answer:
(i) Ammonium nitrate is a highly explosive substance and can not be heated.
(ii) Quicklime (CaO).
(iii) By downward displacement of air or upward delivery as it is lighter than air.
(iv) Ammonia is highly soluble in water so it cannot be collected over water.

Teacher's Note:
a) Ammonium salts other than nitrate (such as ammonium chloride) are preferred with calcium hydroxide for laboratory preparation of ammonia.
b) Acidic drying agents like concentrated sulphuric acid cannot be used because they would react with basic ammonia gas.

Question 7.

(a) From the following organic compounds given below, choose one compound in each case which relates to the description [i] to [iv] :
[Ethyne, ethanol, acetic acid, ethene, methane]
(i) An unsaturated hydrocarbon used for welding purposes.
(ii) An organic compound whose functional group is carboxyl.
(iii) A hydrocarbon which on catalytic hydrogenation gives a saturated hydrocarbon.
(iv) An organic compound used as a thermometric liquid. [4 Marks]

Answer:
(i) Ethyne
(ii) Acetic acid
(iii) Ethene
(iv) Ethanol

Teacher's Note:
a) Ethyne burns with oxygen in oxy-acetylene torches to produce high temperatures suitable for welding.
b) Alkenes and alkynes undergo hydrogenation in the presence of nickel or palladium catalysts to form alkanes.

(b) (i) Why is pure acetic acid known as glacial acetic acid? [2 Marks]
(ii) Give a chemical equation for the reaction between ethyl alcohol and acetic acid.

Answer:
(i) Pure acetic acid on cooling forms an ice like mass so it is called glacial acetic acid.
(ii) CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O (ethanoic acid + ethanol → ethyl ethanoate + water)
This reaction is called esterification.

Teacher's Note:
a) Glacial acetic acid freezes at 16.6 degree C, forming ice-like crystals in cold weather.
b) Esterification reactions are slow and reversible, typically catalyzed by concentrated sulphuric acid.

(c) There are three elements E, F, G with atomic numbers 19, 8, and 17 respectively.
(i) Classify the elements as metals and non-metals. [3 Marks]
(ii) Give the molecular formula of the compound formed between E and G and state the type of chemical bond in this compound. [1 Mark]

Answer:
(i) Electronic configurations:
E (19) = 2, 8, 8, 1 (Metal)
F (8) = 2, 6 (Non-metal)
G (17) = 2, 8, 7 (Non-metal)
Classification: E = Metal, F and G = Non-metal.
(ii) Compound between E (Potassium, valency 1) and G (Chlorine, valency 1): EG (KCl).
Type of chemical bond: Ionic / electrovalent bond.

Teacher's Note:
a) Elements with 1, 2, or 3 valence electrons are typically metals, while those with 5, 6, or 7 valence electrons are non-metals.
b) Ionic bonds are formed by the complete transfer of electrons from a metal to a non-metal, resulting in electrostatic attraction between oppositely charged ions.