sblock Elements 2 Question 8
8. Match the following items in Column I with the corresponding items in Column II.
(2019 Main, 11 Jan II)
| Column I | Column II | ||
|---|---|---|---|
| (i) $\mathrm{Na}{2} \mathrm{CO}{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}$ | A. | Portland cement ingredient |
|
| (ii) $\mathrm{Mg}\left(\mathrm{HCO}{3}\right){2}$ | B. | Castner-Kellner process | |
| (iii) $\mathrm{NaOH}$ | C. | Solvay process | |
| (iv) $\mathrm{Ca}{3} \mathrm{Al}{2} \mathrm{O}_{6}$ | D. | Temporary hardness |
(a) (i) - (D); (ii) - (A); (iii) - (B); (iv) - (C)
(b) (i) - (B); (ii) - (C); (iii) - (A); (iv) - (D)
(c) (i) - (C); (ii) - (B); (iii) - (D); (iv) - (A)
(d) (i) - (C); (ii) - (D); (iii) - (B); (iv) - (A)
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Answer:
Correct Answer: 8. (b)
Solution:
- (i) Washing soda $\left(\mathrm{Na}{2} \mathrm{CO}{3} \cdot 10 \mathrm{H}{2} \mathrm{O}\right)$ is manufactured in Solvay process. In this method, $\mathrm{CO}{2}$ gas is passed through a conc. solution of $\mathrm{NaCl}$ saturated with $\mathrm{NH}_{3}$. It gives ammonium carbonate followed by ammonium hydrogen carbonate.
The obtained $\mathrm{NH}{4} \mathrm{HCO}{3}$ is treated with solution of $\mathrm{NaCl}$ which result in the formation of $\mathrm{NaHCO}{3}$. The crystal obtained are heated to obtain $\mathrm{Na}{2} \mathrm{CO}_{3}$.
$$ \mathrm{NaCl}+\mathrm{NH}{3}+\mathrm{CO}{2}+\mathrm{H}{2} \mathrm{O} \longrightarrow \mathrm{NaHCO}{3}+\mathrm{NH}_{4} \mathrm{Cl} $$
$2 \mathrm{NaHCO}{3} \xrightarrow[-\mathrm{H}{2} \mathrm{O}, \mathrm{CO}{2}]{\longrightarrow} \mathrm{Na}{2} \mathrm{CO}{3} \xrightarrow{\text { Crystallisation }} \mathrm{Na}{2} \mathrm{CO}{3} \cdot 10 \mathrm{H}{2} \mathrm{O}$
(ii) $\mathrm{Mg}\left(\mathrm{HCO}{3}\right){2}$ and $\mathrm{Ca}\left(\mathrm{HCO}{3}\right){2}$ cause temporary hardness to water that can be easily removed by boiling.
(iii) $\mathrm{NaOH}$ is manufactured by Castner-Kellner process.
In this reaction, $\mathrm{Na}$ amalgam flows out and treated with water to give $\mathrm{NaOH}$ and $\mathrm{H}_{2}$ gas. During electrolysis, hydrogen is evolved at cathode and chlorine is evolved at anode, which are the by product of this process.
(iv) Portland cement constitutes, tricalcium aluminosilicate, $3 \mathrm{CaO} \cdot \mathrm{Al}{2} \mathrm{O}{3} \cdot \mathrm{SiO}{2}$, i.e. $\mathrm{Ca}{3} \mathrm{Al}{2} \mathrm{O}{6} \cdot \mathrm{SiO}_{2}$.
