Question

(a) Choosing only substances from the list given in the box below, write equations for the reactions which you would use in the laboratory to obtain:
(i) Sodium sulphate
(ii) Copper sulphate
(iii) Iron (II) sulphate
(iv) Zinc carbonate

Dilute sulphuric acid

Copper Iron Sodium, Zinc

Copper carbonate Sodium carbonate

(b) From the formulae listed below, choose one, in each case, corresponding to the salt having the given description:
AgCl, CuCO₃, CuSO₄·5H₂O, KNO₃, NaCl, NaHSO₄, Pb(NO₃)₂, ZnCO₃, ZnSO₄·7H₂O.
(i) An acid salt.
(ii) An insoluble chloride.
(iii) On treating with concentrated sulphuric acid, this salt changes from blue to white.
(iv) On heating this salt changes from green to black.
(v) This salt gives nitrogen dioxide on heating.

Answer 1

(a) (i) Sodium sulphate is prepared by the neutralisation of soluble base sodium carbonate with dilute sulphuric acid.

${\mathrm{Na}}_2{\mathrm{CO}}_3+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{Na}}_2{\mathrm{SO}}_4+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$

(ii) Copper sulphate is prepared by the reaction between copper carbonate and dilute sulphuric acid.

${\mathrm{CuCO}}_3+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{CuSO}}_4+{\mathrm{H}}_2{\mathrm{CO}}_3$
(iii) Iron (II) sulphate or ferrous sulphate is prepared by the displacement reaction between iron metal and dilute sulphuric acid.

$\mathrm{Fe}+{\mathrm{H}}_2{\mathrm{SO}}_4\stackrel{}{\to }{\mathrm{FeSO}}_4+{\mathrm{H}}_2$

(iv) Preparation of zinc carbonate involves the following steps:

Step I: Zinc sulphate is prepared by the displacement reaction between zinc metal and dilute sulphuric acid.

$\mathrm{Zn}+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{ZnSO}}_4+{\mathrm{H}}_2$
Step II: Zinc sulphate reacts with sodium carbonate to give zinc carbonate.

${\mathrm{ZnSO}}_4+{\mathrm{Na}}_2{\mathrm{CO}}_3\to {\mathrm{ZnCO}}_3+{\mathrm{Na}}_2{\mathrm{SO}}_4$

(b) (i) Sodium hydrogen sulphate, NaHSO₄, is an acid salt.
(ii) Silver chloride, AgCl, is an insoluble chloride.
(iii) ${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}$ changes its colour from blue to white when treated with concentrated sulphuric acid.

CuSO₄.5H₂O → CuSO₄ + 5H₂O

(iv) Copper carbonate, CuCO₃, changes its colour from green to black on heating.

${\mathrm{CuCO}}_3\stackrel{∆}{\to }\mathrm{CuO}+{\mathrm{CO}}_2$

(v) Lead nitrate, Pb(NO₃)₂, gives nitrogen dioxide on heating.

$\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\stackrel{∆}{\to }\mathrm{PbO}+{\mathrm{NO}}_2$