When carbon dioxide is passed through lime water

• GC Metals Non-Metals

When carbon dioxide is passed through lime water, the solution turns milky, but, on prolonged passage, the solution turns clear. This is because

1. the calcium carbonate formed initially is converted to soluble calcium bicarbonate on passage of more carbon dioxide
2. the calcium bicarbonate formed initially is converted to soluble calcium carbonate on passage of more carbon dioxide
3. the reaction is reversible and lime water is regenerated
4. the initially formed insoluble compound is soluble in carbonic acid

Answer

When you first start to bubble carbon dioxide through lime water (calcium hydroxide solution), they react and form calcium carbonate. This isn't very soluble, so you see it as a mist of fine particles of chalk, which we describe as 'the lime water has gone cloudy/ milky'. As you continue to bubble, carbon dioxide dissolves in the water to form carbonic acid, which dissolves the calcium carbonate, so the milkiness disappears.

Here are the reactions: 

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O forming the milkiness 

2H₂CO₃ + CaCO₃ → Ca(HCO₃)₂ + H₂O +CO₂ removing the milkiness again

The correct option is B.