(a) (i) A compound 'X' which is prepared from gypsum has the property of hardening when mixed with proper quantity of water. Identify 'X' and write its chemical formula. (ii) State the difference in chemical composition between baking soda and baking powder. OR (b) Write balanced chemical equation for the reaction that occurs when: (i) blue coloured copper sulphate crystals are heated and (ii) Sodium hydrogen carbonate is heated during cooking.

Option (a)

(i) Identification of 'X' and its chemical formula:

• Name of Compound 'X': Plaster of Paris (Calcium sulphate hemihydrate)
• Chemical Formula: $CaSO_4 \cdot \frac{1}{2}H_2O$

(ii) Difference in chemical composition between baking soda and baking powder:

• Baking Soda: It consists purely of sodium hydrogencarbonate ($NaHCO_3$).
• Baking Powder: It is a mixture containing baking soda ($NaHCO_3$) and a mild, edible acid such as tartaric acid.

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Option (b)

(i) Heating of blue coloured copper sulphate crystals:

When blue copper sulphate crystals ($CuSO_4 \cdot 5H_2O$) are heated, they lose their water of crystallization and turn white anhydrous copper sulphate ($CuSO_4$).

$$CuSO_4 \cdot 5H_2O(s) \xrightarrow{\Delta} CuSO_4(s) + 5H_2O(g)$$

(ii) Heating of sodium hydrogencarbonate during cooking:

When sodium hydrogencarbonate ($NaHCO_3$) is heated during cooking, it decomposes to form sodium carbonate, water, and carbon dioxide gas.

$$2NaHCO_3(s) \xrightarrow{\Delta} Na_2CO_3(s) + H_2O(l) + CO_2(g)$$