Question

the gas to laboratory when sodium carbonate reacts with hydrochloric acid is passed through a lemon water a white precipitate is formed but when the same gas is passed through lime water is exclusive precipilate not a visible why​

Answer 1

The gas evolved when sodium carbonate reacts with dilute hydrochloric acid is Carbon dioxide (CO2).

This gas when bubbled through limewater forms a milky white insoluble precipitate of Calcium Carbonate, but when excess of Carbon dioxide is passed into the limewater, another reaction takes place in which calcium carbonate, excess carbon dioxide and water react to produce soluble Calcium Bicarbonate (Ca(HCO3)2 ). This dissolves in the limewater and hence the precipitate disappears on passing excess of Carbon Dioxide gas.

Reaction:

1) CO2 + Ca(OH)2 -----------> CaCO3 (milky white ppt) + H2O

2) CaCO3 + CO2 (excess) + H2O -----------> Ca (HCO3)2 (soluble in water)