Question

2. 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?

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Answer 1

When dilute hydrochloric acid reacts with sodium carbonate, then sodium chloride, carbon dioxide and water are formed. CO2 gas is liberated during the reaction.

$\sf \:{\red{ Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2 (g) + H2(O)(l)}}$

When carbon dioxide gas formed in the form of brisk effervescence is passed through lime water, it turns the lime water milky. If excess of carbon dioxide gas is passed through the milky lime water, the solution becomes clear again. This confirms the presence of carbon dioxide gas.

$\sf \: @WildCat7083$

Answer 2

Explanation:

Because when excess carbon dioxide is passed through lime water calcium carbonate is a white precipitate formed, which turns lime water milky. But when excess CO2 is passed through it, CaHCO3 is formed which is not a precipitate.