Question

A. (i) What is the percentage composition of calcium in calcium nitrate? [1 mark]
(ii) At 27 $°$C, a balloon is filled with 3 L air. The volume of the balloon when the temperature is 54 $°$C is . [1 mark]

B. Distinguish between the following pair of compounds based on the reagent given in the bracket. [2 marks]
(i) Ferrous sulphate solution and ferric sulphate solution. (using sodium hydroxide solution)
(ii) Dilute hydrochloric acid and dilute sulphuric acid. (using lead nitrate solution)

C. The pH value of three solutions A, B and C are given in the table.

Solution	pH Value
A	12
B	2
C	7

Answer the following questions. [3 marks]
(i) Which solution will have no effect on litmus solution?
(ii) Which solution will liberate $C{O}_2$ when reacted with sodium carbonate?
(iii) Which solution will turn red litmus solution blue?


D. Study the extract of the Periodic table given below and answer the questions. Give the aphabet correpsonding to the element. (Do not repeat the element.) [3 marks]

(i) Which element forms electrovalent compound with G?
(ii) The ion of which element will migrate towards the cathode during electrolysis?
(iii) Which non-metallic element has the valency of 2?

Answer 1

A. (i) Percentage composition of calcium in $Ca(N{O}_3{)}_2$
= Mass of calcium in $Ca(N{O}_3{)}_2$/Molar mass of $Ca(N{O}_3{)}_2$ $\times$ 100

Mass of calcium in $Ca(N{O}_3{)}_2$
= Number of atoms of calcium in $Ca(N{O}_3{)}_2$ $\times$ 40
= 1 $\times$ 40 = 40 amu

Molar mass of $Ca(N{O}_3{)}_2$
= (40 $\times$ 1) + 2 [(14) + (3 $\times$ 16)] = 164 amu

Percentage composition of calcium
= 40/164 $\times$ 100 = 24.39 %
≈ 24 % [1 mark]
(ii) According to Charles' Law at constant pressure the volume of a fixed amount of gas is directly proportional to its temperature-
i.e $V$ α $T$
Thus, $\frac{V_1}{T_1}=\frac{V_2}{T_2}$, where
$V_1$ = initial volume; $V_2$ = final volume
$T_1$ = initial temperature; $T_2$ = final temperature
$V_1$ = 2 L, $V_2$ = ?
$T_1$ = 273 + 27 = 300 K
$T_2$ = 273 + 54 = 327 K
Therefore, $V_2=\frac{V_1\times T_2}{T_1}$= $\frac{3\times 327}{300}$ = 3.27 L [1 mark]

B. (i) Ferrous sulphate solution gives dirty green precipitate with sodium hydroxide solution. On the other hand, ferric sulphate solution gives a reddish brown precipiate with sodium hydroxide. [1 mark]

(ii) On adding lead nitrate solution, if white precipitate is formed which dissolves on heating, then it is dilute HCl. If white precipiate does not dissolve on heating, it is dilute $H_{2}S{O}_4$. [1 mark]


C. (i) Solutions with a pH of 7 are neutral. Hence, solution C will have no effect on litmus solution. [1 mark]

(ii) Acidic solution reacts with metal carbonate to liberate carbon dioxide gas. An acidic solution is any aqueous solution which has a pH < 7.0. Hence, solution B will liberate carbon dixoide gas on reaction with metal carbonates. [1 mark]

(iii) The colour of litmus solution changes from red to blue in a basic solution. Solutions with a pH greater than 7 are basic. Hence solution A will turn red litmus solution blue. [ 1mark]

D. (i) Electrovalent compounds are formed by complete transfer of electrons. Group 2 metal will form electrovalent compound with group 17 element. So, B will form electrovalent compound with G. [1 mark]

(ii) Cations are positively charged ions while cathode is positively charged electrode. Thus, they are attracted towards cathode during electrolysis. A will form positive ions which migrate towards cathode. [1 mark]

(iii) E is non-metallic and has a valency of 2 as it belongs to group 16. [1 mark]