Question

The gas liberated when sodium carbonate reacts with dilute hydrochloric acid

is passed through lime water, a white precipitate is formed. But when the same

gas is passed through lime water in excess, precipitate is not visible. Why​

Answer 1

Carbon dioxide gas is liberated when hydrochloric acid reacts with sodium hydrogen carbonate

Answer 2

Answer:

Due to the formation of Calcium hydrogencarbonate precipitate is not visible.

Explanation:

When sodium carbonate reacts with dilute hydrochloric acid,

$Na_{2}CO_{3}+2HCl(dil)\rightarrow 2NaCl+CO_{2}+H_{2}O$

CO₂ is liberated which reacts with Limewater(Ca(OH)₂ to form CaCO₃ (milky white ppt).

On passing excess CO₂, milkiness disappears due to formation of Calcium Carbonate Ca(HCO₃)₂.

When an excess of carbon dioxide is passed through lime water, the formed milkiness disappears. This is due to the formation of calcium carbonate, which is colourless and insoluble in water.

$2CaCO_{3}+H_{2}O+2CO_{2}(excess)\rightarrow 2Ca(HCO_{3})_{2}$

A colourless solution of calcium hydrogencarbonate is formed in the end.

Here in the question it was not clearly mentioned about CO₂ being in excess or limewater being in excess. But I guess I answered your concern as this was the most probable question that could be asked.