Excess sulphur (IV) oxide gas was bubbled through a solution of sodium hydroxide containing phenolphthalein. (I) state what is observed (11) write the equations for the reaction in (a) above? ?

(I) The solution will turn pink, indicating the formation of sodium sulphite.

(II) The equation for the reaction is:
SO2 + 2NaOH -> Na2SO3 + H2O

(I) Observation:
The solution gradually turns colorless.

(II) Equations for the Reactions:

Step 1: Sulphur (IV) oxide gas reacts with water to form sulphurous acid (H2SO3):
```
SO2(g) + H2O(l) → H2SO3(aq)
```

Step 2: Sulphurous acid reacts with sodium hydroxide to form sodium sulfite:
```
H2SO3(aq) + 2NaOH(aq) → Na2SO3(aq) + H2O(l)
```

Step 3: Excess sulphur (IV) oxide gas reacts with sodium sulfite to form sodium thiosulfate:
```
SO2(g) + Na2SO3(aq) → Na2S2O3(aq)
```

Overall Equation:
```
SO2(g) + 2NaOH(aq) → Na2S2O3(aq) + H2O(l)
```

Note: Phenolphthalein is an acid-base indicator that turns colorless in the presence of an acidic solution. The gradual decolorization of phenolphthalein in the experiment indicates the formation of acidic sulphurous acid in the first step.