ICSE Class 10 Chemistry Board Exam Question Paper 2007 with Solutions

ICSE Class 10 Chemistry Board Exam Question Paper 2007 with Solutions

SECTION - I (40 Marks)

(Compulsory : Attempt all questions.)

Question 1.

(a) From the list given below, select the word(s) required to correctly complete blanks (i) to (v) in the following passage :
ammonia, ammonium, carbonate, carbon dioxide, hydrogen, hydronium, hydroxide, precipitate, salt, water.
A solution X turns blue litmus red, so it must contain (i) ............ ions; another solution Y turns red litmus blue and therefore, must contain (ii) ............ ions.
When solutions X and Y are mixed together, the products will be a (iii) .......... and (iv) ............ . If a piece of magnesium were put into solution X, (v) ............ gas would be evolved.
(Note : words chosen from the list are to be used only once. Write the answers as (i) (i), (ii), (iii) and so on. Do not copy the passage). [5 Marks]

Answer:
(i) hydronium
(ii) hydroxide
(iii) salt
(iv) water
(v) Hydrogen.

Teacher's Note:
a) Acidic solutions contain hydronium ions which turn blue litmus red, while basic solutions contain hydroxide ions which turn red litmus blue.
b) Ensure proper numbering corresponding strictly to blanks (i) to (v) as required.

(b) From the list of characteristics given below, select the five which are relevant to non-metals and their compounds :
A. Ductile
B. Conduct electricity
C. Brittle
D. Acidic oxides
E. Basic oxides
F. Discharged at anode
G. Discharged at cathode
H. Ionic Chlorides
I. Covalent Chlorides
J. Reaction with dilute Sulphuric acid yields hydrogen
K. 1, 2 or 3 valence electrons
L. 5, 6 or 7 valence electrons
(Write the five letters corresponding to the correct characteristics) [5 Marks]

Answer:
C, D, F, I, L.

Teacher's Note:
a) Non-metals form covalent chlorides, acidic oxides, are brittle in solid state, possess 5, 6, or 7 valence electrons, and anions are discharged at the anode during electrolysis.
b) Students must write only the letters representing the correct options as instructed.

(c) A group of elements in the Periodic Table are given below (Boron is the first member of the group and Thallium is the last).
Boron, Aluminium, Gallium, Indium, Thallium
Answer the following questions in relation to the above group of elements :
(i) Which elements has the most metallic character ? [1 Mark]
(ii) Which element would be expected tohave the highest electro-negativity ? [1 Mark]
(iii) If the electronic configuration of Aluminium is 2, 8, 3, how many electrons are there in the outer shell of Thallium ? [1 Mark]
(iv) The atomic number of Boron is 5. Write the chemical formula of the compound formed when Boron reacts with Chlorine. [1 Mark]
(v) Will the elements in the group to the right of this Boron group be more metallic or less metallic in character ? Justify your answer. [1 Mark]

Answer:
(i) Thallium
(ii) Boron
(iii) Three
(iv) BCl₃
(v) Less metallic. Because on moving towards right in periodic table metallic character decreases.

Teacher's Note:
a) Metallic character increases down the group and electronegativity decreases down the group.
b) Elements of the same group share the same number of valence electrons, hence Thallium has 3 valence electrons like aluminium.

(d) Match the following :
Column A
1. Acid salt
2. Mixed salt
3. Complex salt
4. Double salt
5. Normal salt
Column B
A. Sodium potassium carbonate
B. Alum
C. Sodium carbonate
D. Sodium zincate
E. Sodium hydrogencarbonate [5 Marks]

Answer:
1 - E, 2 - A, 3 - D, 4 - B, 5 - C.

Teacher's Note:
a) Acid salts contain replaceable hydrogen ions (e.g., NaHCO₃), whereas normal salts do not.
b) Double salts dissociate into simple ions completely in solution, unlike complex salts.

(e) Give the IUPAC names of the following compounds numbered (i) to (v). The IUPAC names of the compounds on the left are to guide you into giving the correct IUPAC names of the compounds on the right.
Propene
Pentan-2-ol
2, 2-dimethylpropane
Propanoic acid
1, 2-dibromoethane
(i)
[Figure: Structure of CH₃-CH₂-C≡C-H]
(ii)
[Figure: Structure of CH₃-CH₂-CH(OH)-CH₂-CH₃]
(iii)
[Figure: Structure of CH₃-C(CH₃)₂-CH₂-CH₃]
(iv)
[Figure: Structure of CH₃-CH₂-COOH]
(v)
[Figure: Structure of CH₃-CH(Cl)-CH₂-Cl] [5 Marks]

Answer:
(i) Propyne
(ii) Pentan-3-ol
(iii) 2-methylpropane
(iv) Ethanoic acid
(v) 1, 2-dichloroethane

Teacher's Note:
a) IUPAC naming follows the longest carbon chain rule and lowest locant rule for functional groups or unsaturation.
b) Pay close attention to functional groups such as carboxylic acids, alcohols, alkynes, and halogen substituents.

(f) A sample of ammonium nitrate when heated yields 8.96 litres of steam (measured at stp).
NH₄NO₃ → N₂O + 2H₂O
(i) What volume of dinitrogen oxide is produced at the same time as 8.96 litres of steam ? [1 Mark]
(ii) What mass of ammonium nitrate should be heated to produce 8.96 litres of steam ? (Relative molecular mass of ammonium nitrate is 80). [2 Marks]
(iii) Determine the percentage of oxygen in ammonium nitrate (O = 16) [2 Marks]

Answer:
(i) From the equation:
NH₄NO₃ → N₂O + 2H₂O
1 vol : 2 vol.
When 2 vol. of steam is produced, 1 vol. of N₂O is formed.
Volume of N₂O = \( \frac{8.96}{2} \) = 4.48 litre.
(ii) 1 mole (80 g) of NH₄NO₃ produces \( 2 \times 22.4 \) litres of steam at stp.
Since \( 2 \times 22.4 \) l of steam is produced from 80 g of NH₄NO₃,
8.96 l of steam will be produced from \( \frac{80 \times 8.96}{2 \times 22.4} \) = 16 g of NH₄NO₃.
(iii) % of oxygen in NH₄NO₃ = \( \frac{3 \times 16 \times 100}{80} \) = 60%.

Teacher's Note:
a) Apply Gay-Lussac's Law of combining volumes for gas stoichiometry problems.
b) Use molar mass and mass percentage formulas accurately for percentage composition questions.

(g) Write balanced chemical equations for the following reactions :
(i) Lead sulphate from lead nitrate solution and dilute sulphuric acid. [1 Mark]
(ii) Copper sulphate from copper and concentrated sulphuric acid. [1 Mark]
(iii) Lead chloride from lead nitrate solution and sodium chloride solution. [1 Mark]
(iv) Ammonium sulphate from ammonia and dilute sulphuric acid. [1 Mark]
(v) Sodium chloride from sodium carbonate solution and dilute hydrochloric acid. [1 Mark]

Answer:
(i) Pb(NO₃)₂ + H₂SO₄ → PbSO₄ + 2HNO₃
(ii) Cu + 2H₂SO₄ → CuSO₄ + 2H₂O + SO₂
(iii) Pb(NO₃)₂ + 2NaCl → PbCl₂ + 2NaNO₃
(iv) 2NH₃ + H₂SO₄ → (NH₄)₂SO₄
(v) Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Teacher's Note:
a) Ensure all chemical equations are fully balanced with proper state symbols or reactant-product stoichiometric coefficients.
b) Note that concentrated sulphuric acid acts as an oxidizing agent with metals like copper.

(h) Choose A, B, C or D to match the descriptions (i) to (v) below. Some alphabets may be repeated.
A. non-electrolyte
B. strong electrolyte
C. weak electrolyte
D. metallic conductor
(i) Molten ionic compound.
(ii) Carbon tetrachloride
(iii) An aluminium wire
(iv) A solution containing solvent molecules solute molecules and ions formed by the dissociation of solute molecules.
(v) A sugar solution with sugar molecules and water molecules. [5 Marks]

Answer:
(i) - B strong electrolyte
(ii) - A non-electrolyte
(iii) - D metallic conductor
(iv) - C weak electrolyte
(v) - A non-electrolyte

Teacher's Note:
a) Molten ionic compounds conduct electricity well due to free mobile ions, hence acting as strong electrolytes.
b) Weak electrolytes partially dissociate, resulting in a mixture of ions and unionised molecules in solution.

SECTION - II (40 Marks)

(Answer any four questions from this section)

Question 2.

(a) Some properties of Sulphuric acid are listed below. Choose the property A, B, C or D which is responsible for the reactions (i) to (v). Some properties may be repeated :
A. Acid
B. Dehydrating agent
C. Non-volatile acid
D. Oxidizing agent
(i) C₁₂H₂₂O₁₁ + nH₂SO₄ → 12C + 11H₂O + nH₂SO₄
(ii) S + 2H₂SO₄ → 3SO₂ + 2H₂O
(iii) NaCl + H₂SO₄ → NaHSO₄ + HCl
(iv) CuO + H₂SO₄ → CuSO₄ + H₂O
(v) Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂ [5 Marks]

Answer:
(i) - B
(ii) - D
(iii) - C
(iv) - A
(v) - A

Teacher's Note:
a) Concentrated sulphuric acid acts as a dehydrating agent by removing elements of water from compounds like sugar.
b) It acts as a non-volatile acid in the preparation of more volatile acids like hydrochloric acid from its salts.

(b) (i) Name the acid formed when sulphur dioxide dissolves in water. ** [1 Mark]
(ii) Name the gas released when sodium carbonate is added to a solution of sulphur dioxide. ** [1 Mark]
(iii) What are the two necessary conditions for the direct combination of sulphur dioxide and chlorine forming sulphuryl chloride ? ** [1 Mark]
(iv) State the property of suphur dioxide which causes potassium permanganate to change its colour from purple to colourless. ** [2 Marks]
(** Answer has not been given due to out of present syllabus.)

Answer:
(i) Sulphurous acid (H₂SO₃).
(ii) Carbon dioxide (CO₂).
(iii) Presence of sunlight (or ultraviolet light) and a catalyst like activated charcoal.
(iv) Reducing property (acting as a strong reducing agent).

Teacher's Note:
a) Sulphur dioxide dissolves in water to form sulphurous acid.
b) SO₂ reduces acidified potassium permanganate solution, causing the purple colour to discharge.

Question 3.

(a) (i) Of the two gases, ammonia and hydrogen chloride, which is more dense ? Name the method of colection of this gas. [1 Mark]
(ii) Give one example of a reaction between the above two gases that produces a solid compound. [2 Marks]

Answer:
(i) Hydrogen chloride is more dense. It is collected by upward displacement of air.
(ii) Hydrogen chloride and ammonia gas react together to give solid ammonium chloride.
NH₃ + HCl → NH₄Cl

Teacher's Note:
a) Vapour density of HCl is 18.25 while that of NH₃ is 8.5, making HCl denser than air.
b) The reaction produces dense white fumes of solid ammonium chloride.

(b) Write a balanced equation for a reaction in which ammonia is oxidized by :
(i) a metal oxide;
(ii) a gas which is not oxygen. [2 Marks]

Answer:
(i) 3CuO + 2NH₃ → 3Cu + N₂ + 3H₂O
(ii) 2NH₃ + 3Cl₂ → 6HCl + N₂

Teacher's Note:
a) Ammonia acts as a reducing agent when passed over heated metallic oxides.
b) Chlorine gas oxidizes ammonia to nitrogen gas with the formation of hydrogen chloride.

(c) The figure given below illustrates the apparatus used in the laboratory preparation of nitric acid.
[Figure: Laboratory preparation of nitric acid showing glass retort containing potassium nitrate and concentrated sulphuric acid, heated by burner, connected to a cooled glass receiver immersed in cold water where liquid nitric acid C collects]
(i) Name A (a liquid), B (a solid) and C (a liquid). (Do not give the formula) [3 Marks]
(ii) Write an equation to show how nitric acid undergoes decomposition. [1 Mark]
(iii) Write the equation for the reaction in which copper is oxidized by concentrated nitric acid. [1 Mark]

Answer:
(i) A - Conc. Sulphuric acid, B - Potassium Nitrate, C - Nitric acid.
(ii) 4HNO₃ → 2H₂O + 4NO₂ + O₂
(iii) Cu + 4HNO₃ → Cu(NO₃)₂ + 2H₂O + 2NO₂

Teacher's Note:
a) Nitric acid is prepared by heating a nitrate salt like potassium or sodium nitrate with concentrated sulphuric acid in an all-glass apparatus.
b) Concentrated nitric acid acts as a powerful oxidizing agent, oxidizing copper to copper(II) nitrate while releasing nitrogen dioxide gas.

Question 4.

(a) The following is an extract from 'Metals in the Service of Man, Alexander and Street / Pelican 1976' :
'Alumina (aluminium oxide) has a very high melting point of over 2000°C so that it cannot readily be liquefied. However, conversionof alumina to aluminium and oxygen, by electrolysis, can occur when it is dissolved in some other substance.'
(i) Which solutionis used to react with bauxite as a first step in obtaining pure aluminium oxide ? [1 Mark]
(ii) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the equation for thisreaction. [1 Mark]
(iii) Name the element which serves both as the anode and the cathode in the extraction of aluminium. [1 Mark]
(iv) Write the extraction of aluminium by electrolysis. [1 Mark]
(v) Give the equation for the reaction which occurs at the anode when aluminium in purified by electrolysis. [1 Mark]

Answer:
(i) Sodium hydroxide solution.
(ii) 2Al(OH)₃ \( \xrightarrow{\Delta} \) Al₂O₃ + 3H₂O
(iii) Carbon.
(iv) Al⁺⁺⁺ + 3e^- → Al
(v) Al → Al⁺⁺⁺ + 3e^-

Teacher's Note:
a) Bauxite is leached with concentrated sodium hydroxide solution (Bayer's process) to obtain pure alumina.
b) Carbon blocks serve as both anode and cathode in Hall-Heroult's electrolytic reduction process.

(b) (i) Name the charged particles which attract one another to form electrovalent compounds. [1 Mark]
(ii) In the formation of electrovalent compounds, electrons are transferred from one element to another. How are electrons involved in the formation of a covalent compound ? [1 Mark]
(iii) The electronic configuration of nitrogen is 2, 5. How many electrons in the outer shell of a nitrogen atom are not involved in the formation of a nitrogen molecule ? [1 Mark]
(iv) In the formation of magnesium chloride (by direct combination between magnesium and chlorine), name the substance that is oxidized and the substance that is reduced. [2 Marks]

Answer:
(i) Cations and anions.
(ii) Electrons are shared.
(iii) Two electrons (one lone pair per nitrogen atom).
(iv) Magnesium is oxidised, chlorine is reduced.

Teacher's Note:
a) Electrovalent compounds are formed by electrostatic attraction between oppositely charged ions.
b) In redox terms, loss of electrons is oxidation (magnesium) and gain of electrons is reduction (chlorine).

Question 5.

Copy and complete the following table relates to three homologous series of Hydrocarbons : [10 Marks]

Answer:

Completed Table of Hydrocarbon Homologous Series

Teacher's Note:
a) Alkenes and alkynes undergo addition reactions due to unsaturation, whereas alkanes undergo substitution reactions.
b) Verify general formulas carefully: \( C_nH_{2n+2} \) for alkanes, \( C_nH_{2n} \) for alkenes, and \( C_nH_{2n-2} \) for alkynes.

Question 6.

(a) (i) HCl, HNO₃ and H₂SO₄ are the formula of three compounds.
Which of these compounds has the highest boiling point and which has the lowest ? [1 Mark]
(ii) Dilute hydrochloric acid and dilute sulphuric acid are both colourless solutions. How will the addition of barium chloride solution to each help to distinguish between the two ? [2 Marks]
(iii) You enter a laboratory after a Class has completed the Fountain Experiment. How will you be able to tell whether the gas used in the experiment was hydrogen chloride or ammonia ? [2 Marks]

Answer:
(i) H₂SO₄ has highest boiling point while HCl has lowest boiling point.
(ii) When barium chloride solution is added to dil. hydrochloric acid no ppt is seen but when barium chloride solution is added to dil. sulphuric acid a white ppt is observed.
(iii) If solution in inverted flask is blue, the gas used was ammonia and if solution in inverted flask is red the gas used was hydrogen chloride.

Teacher's Note:
a) Sulphuric acid has a high boiling point due to strong intermolecular hydrogen bonding.
b) Barium chloride gives a white precipitate of barium sulphate with sulphuric acid / sulphate ions, insoluble in dil. HCl.

(b) Write balanced equations for the reaction of dilute hydrochloric acid with each of the following :
(i) iron [1 Mark]
(ii) sodium hydrogencarbonate [1 Mark]
(iii) iron (II) sulphide [1 Mark]
(iv) sodium sulphite [1 Mark]
(v) sodium thiosulphate solution. [1 Mark]

Answer:
(i) Fe + 2HCl → FeCl₂ + H₂
(ii) NaHCO₃ + HCl → NaCl + H₂O + CO₂
(iii) FeS + 2HCl → FeCl₂ + H₂S
(iv) Na₂SO₃ + 2HCl → 2NaCl + H₂O + SO₂
(v) Na₂S₂O₃ + 2HCl → 2NaCl + S + H₂O + SO₂

Teacher's Note:
a) Dilute acids react with reactive metals to evolve hydrogen gas.
b) Metal sulphites evolve sulphur dioxide, and metal sulphides evolve hydrogen sulphide with dilute hydrochloric acid.

Question 7.

(a) A compound X consists of 4.8% carbon and 95.2% bromine by mass.
(i) Determine the empirical formula of this compound working correct to one decimal place (C = 12; Br = 80). [2 Marks]
(ii) If the vapour density of the compound is 252, what is the molecular formula of the compound ? [2 Marks]
(iii) Name the type of chemical reaction by which X can be prepared from ethane. [1 Mark]

Answer:
(i) Calculation of Empirical formula :

Empirical formula = CBr₃.
(ii) Relative molecular mass = VD × 2
= 252 × 2
= 504
Empirical mass = 12 + 80 × 3
= 252
n = \( \frac{504}{252} \) = 2
Molecular formula = (CBr₃)₂ = C₂Br₆.
(iii) By substitution reaction.

Teacher's Note:
a) Always calculate relative number of moles by dividing percentage by atomic mass, then find the simplest whole-number ratio.
b) Molecular formula is obtained by multiplying the empirical formula by n, where n = (Molecular Mass / Empirical Formula Mass).

(b) Salts A, B, C, D and E undergo reactions (i) to (v) respectively. Identify the anion present in these salts on the basis of these reactions. Tabulate your answers in the format given below :
(i) When silver nitrate solution is added to a solution of A, a white precipitate, insoluble in dilute nitric acid, is formed.
(ii) Addition of dilute hydrochloric acid to B produces a gas which turns lead acetate paper black.
(iii) When a freshly prepared solution of ferrous sulphate is added to a solution of C and concentrated sulphuric acid is gently poured from the side of the test-tube, a brown ring is formed.
(iv) When dilute sulphuric acid is added to D a gas is produced which turns acidified potassium dichromate solution from orange to green.
(v) Addition of dilute hydrochloric acid to E produces an effervescence. The gas produced turns limewater milky but does not affected acidified potassium dichromate solution.
[Figure: Table with columns Salt (A to E) and Anion] [5 Marks]

Answer:

Table of Salt Identification and Anions

Teacher's Note:
a) Analytical chemistry tests for anions rely on characteristic gas evolution or specific precipitate formation.
b) Chloride ions give a curdy white precipitate with silver nitrate insoluble in nitric acid, while nitrate ions give a brown ring test with FeSO₄ and conc. H₂SO₄.