Sodium hydroxide + Sulphur dioxide

Sodium hydroxide reacts with sulphur dioxide to give sodium sulphite solution.
2NaOH(aq) + SO2(aq) → Na2SO3(aq) + H2O(l)
or 2OH-(aq) + SO2(aq) →SO32-(aq) + H2O(l)

Excess sulphur dioxide reacts with sodium hydroxide to give sodium hydrogensulphite solution.
Na2SO3(aq) + SO2(g) + H2O(l) → 2NaHSO3(aq)
or SO32-(aq) + SO2(g) + H2O(l) → 2HSO3-(aq)

Observations : Sulphur dioxide gas is absorbed by sodium hydroxide solution. There is no other apparent observable change because all products are soluble in water to give colourless solutions.