Question

A gas is evolved when ethanol reacts with sodium. The gas evolved is:
(A) hydrogen
(B) carbon dioxide
(C) oxygen
(D) none of the above

Answer 1

Write the molecular formula of ethanol. Find out what happens when alcohol reacts with sodium metal. Write the reaction which takes place when ethanol reacts with sodium metal. Identify the products of the reaction.

Complete step by step solution:
- Ethanol is an alcohol having the molecular formula, ${{C}_{2}}{{H}_{5}}OH$.
- Alcohols react with sodium metals to form sodium alkoxide and hydrogen gas which is evolved.
- Ethanol reacts with sodium metal to form sodium ethoxide and there is the evolution of hydrogen gas.
$2{{C}_{2}}{{H}_{5}}OH+2Na\to 2{{C}_{2}}{{H}_{5}}ONa+{{H}_{2}}$
- Therefore, a gas evolved when ethanol reacts with sodium is hydrogen.

Therefore, the answer is option (A).

Note: This reaction of ethanol and sodium is used as a confirmatory test to detect the presence of ethanol in a mixture of organic compounds. In this test, a tiny piece of sodium is added to a suspected alcoholic organic compound. If the addition of sodium metal to the liquid gives effervescence or fast-rising bubbles which indicate the evolution of hydrogen gas then it is confirmed that the unknown sample is ethanol. If adding sodium metal to the liquid doesn’t give any bubbles then the sample is not alcohol. This is a preliminary test but there are more tests which exactly confirm the presence of ethanol.