From an experiment to study the properties of acetic acid. Answer the following questions :
(a) Name the substance which on addition to acetic acid produces carbon dioxide gas. Give relevant chemical equation for the above ?
(b) How is `CO_(2)` gas tested in the laboratory?

Explanation

(a) Acetic acid produces `CO_(2)` gas when a pinch of sodium hydrogen carbonate `(NaHCO_(3))` is added to the tube containing the acid.
`CH_(3)COOH(aq)+NaHCO_(3)(s)rarrCH_(3)COONa(aq)+H_(2)O(aq)+CO_(2)(g)`
(b) `CO_(2)(g)` can be tested by passing the vapours of the gas into lime water taken in a test tube. Initially lime water becomes milky which disappears when the gas is passed in excess.
`underset("(Lime water)")(Ca(OH)_(2)(aq))+CO_(2)(g)rarrunderset("(Milky)")(CaCO_(3)(s))+H_(2)O(aq)`
`underset("(Milky)")(Ca(CO_(3))(s))+CO_(2)(g)+H_(2)O(aq)rarrunderset("(Colourless)")(Ca(HCO_(3))_(2)(aq))`