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(b) During extraction of metals, electrolytic refining is used to obtain pure metals.
(i) Which material will be used as cathode and anode for refining of zinc metal by this process ?
(ii) Name the electrolyte used in this process. Where do we get pure zinc after passing electric current ?
(iii) How does zinc prevent rusting of iron ? Also, name the process.
(i) Which material will be used as cathode and anode for refining of zinc metal by this process ?
(ii) Name the electrolyte used in this process. Where do we get pure zinc after passing electric current ?
(iii) How does zinc prevent rusting of iron ? Also, name the process.
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(a) (i) (I) $\ce{2HgS(s) + 3O2(g) ->[Heat] 2HgO(s) + 2SO2(g)}$
$\ce{2HgO(s) ->[Heat] 2Hg(l) + O2(g)}$ (1)
(II) $\ce{ZnCO3(s) ->[Heat] ZnO(s) + CO2(g)}$
$\ce{ZnO(s) + C(s) -> Zn(s) + CO(g)}$ (1)
(III) At cathode $\ce{Na+ + e- -> Na}$
At anode $\ce{2Cl- -> Cl2 + 2e-}$ (1)
(ii) (I) Because movement of ions in solid state is not possible due to its
rigid structure. (1)
(II) A large amount of heat energy is required to overcome strong
electrostatic forces of attraction between oppositely charged ions
in ionic compounds. (1)
OR
(b) (i)
$\bullet$ Cathode – Thin strip of pure zinc metal ($\frac{1}{2}$)
$\bullet$ Anode – Impure zinc metal ($\frac{1}{2}$)
(ii)
$\bullet$ A solution of Zinc salt like $\ce{ZnSO4}$. (1)
$\bullet$ On the cathode. (1)
(iii)
$\bullet$ Zinc forms a protective layer on iron preventing reaction
of air and water with iron surface. (1)
$\bullet$ Galvanisation. (1)
$\ce{2HgO(s) ->[Heat] 2Hg(l) + O2(g)}$ (1)
(II) $\ce{ZnCO3(s) ->[Heat] ZnO(s) + CO2(g)}$
$\ce{ZnO(s) + C(s) -> Zn(s) + CO(g)}$ (1)
(III) At cathode $\ce{Na+ + e- -> Na}$
At anode $\ce{2Cl- -> Cl2 + 2e-}$ (1)
(ii) (I) Because movement of ions in solid state is not possible due to its
rigid structure. (1)
(II) A large amount of heat energy is required to overcome strong
electrostatic forces of attraction between oppositely charged ions
in ionic compounds. (1)
OR
(b) (i)
$\bullet$ Cathode – Thin strip of pure zinc metal ($\frac{1}{2}$)
$\bullet$ Anode – Impure zinc metal ($\frac{1}{2}$)
(ii)
$\bullet$ A solution of Zinc salt like $\ce{ZnSO4}$. (1)
$\bullet$ On the cathode. (1)
(iii)
$\bullet$ Zinc forms a protective layer on iron preventing reaction
of air and water with iron surface. (1)
$\bullet$ Galvanisation. (1)