Write the equations for the preparation of chlorine and its reaction with NaOH. Explain the action of chlorine on litmus and calculate the volume of chlorine at S.T.P.

From the equation, 1 mole of $\text{Ca(OH)}_2$ reacts with 1 mole of $\text{Cl}_2$.
Therefore, moles of $\text{Cl}_2$ required = $0.050 \text{ mol}$.

5. (c)

(i) On warming ammonium trioxonitrate (V) ($\text{NH}_4\text{NO}_3$) with sodium hydroxide solution, a pungent-smelling gas (ammonia) is evolved, which turns damp red litmus paper blue.

(ii) Ammonium trioxocarbonate (IV) ($(\text{NH}_4)_2\text{CO}_3$) leaves no residue on being heated because it decomposes completely into gaseous products (ammonia, carbon dioxide, and water vapor), leaving no solid behind.

6. (a)

(i) To remove the sediment in a sample of water:
Filtration. Pass the water through filter paper or a fine sieve to separate insoluble solid particles.

(ii) To soften temporarily hard water without heating it:
Clark's process (adding a calculated amount of calcium hydroxide). The calcium hydroxide reacts with soluble hydrogen carbonates to form insoluble calcium carbonate, which precipitates out.

(iii) To obtain pure water from muddy water:
Distillation. First, filter the muddy water to remove suspended particles, then boil the filtered water and condense the steam to collect pure water.

(iv) To remove oxygen and moisture from a sample of air:
To remove oxygen, pass the air over heated copper turnings. To remove moisture, pass the air through a drying agent such as concentrated sulfuric acid or anhydrous calcium chloride.

6. (b)

(i) Alums are double salts.

(ii) The function of alum in water treatment plants is as a *co