sblock Elements 2 Question 3
3. A hydrated solid
(a) baking soda and soda ash
(b) washing soda and soda ash
(c) baking soda and dead burnt plaster
(d) washing soda and dead burnt plaster
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Answer:
Correct Answer: 3. (c)
Solution:
- Baking soda $\left(\mathrm{NaHCO}{3}\right)
$$
\underset{\text { Gypsum }}{\mathrm{CaSO}{4} \cdot 2 \mathrm{H}{2} \mathrm{O}} \xrightarrow[-1 / 2 \mathrm{H}{2} \mathrm{O}]{\stackrel{380-393 \mathrm{~K}}{\longrightarrow}} \mathrm{CaSO}{4} \cdot \frac{1}{2} \mathrm{H}{2} \mathrm{O} \xrightarrow[\text { Plaster of Paris }]{\stackrel{>393 \mathrm{~K}}{-\frac{1}{2} \mathrm{H}{2} \mathrm{O}}} \underset{
Therefore, the reaction takes place as follows :
$$ \underset{\text { Washing soda }}{\mathrm{Na}{2} \mathrm{CO}{3} \cdot 10 \mathrm{H}{2} \mathrm{O}} \xrightarrow[-9 \mathrm{H}{2} \mathrm{O}]{<373 \mathrm{~K}} \underset{\text { Monohydrate }}{\mathrm{Na}{2} \mathrm{CO}{3} \cdot \mathrm{H}{2} \mathrm{O} \xrightarrow[-\mathrm{H}{2} \mathrm{O}]{>37 \mathrm{~K}}} \underset{\text { Anhydrous white powder }}{\mathrm{Na}{2} \mathrm{CO}{3}} $$
