Question

Give chemical test to distinguish: (i) Ethyl alcohol and sec-propyl alcohol (ii) Acetaldehyde and acetic acid

Answer 1

Hint: (i) We can select a reagent that reacts at different rates with primary and secondary alcohols. That test will provide the required difference.
(ii)We have to select a reagent that precipitates with one compound but does not react with another compound.

Complete Step by step answer: (i) Ethyl alcohol is a primary alcohol and sec-propyl alcohol is a secondary alcohol. To distinguish ethyl alcohol and sec-propyl alcohol, you can carry out Lucas test. Lucas test is used to distinguish between primary, secondary and tertiary alcohols. Lucas reagent is a mixture of concentric hydrochloric acid and anhydrous zinc chloride. At room temperature ethyl alcohol (a primary alcohol) does not form any turbidity with Lucas reagent.
Sec-propyl alcohol (a secondary alcohol) forms any turbidity with Lucas reagent within 5-10 minutes.
Lucas reagent converts an alcohol to alkyl halide. The turbidity formed during Lucas test is due to formation of alkyl halide.

(ii) To distinguish acetaldehyde and acetic acid you can use a silver mirror test.
You can use Tollen’s reagent to carry out a silver mirror test. The Tollen’s reagent is an ammoniacal silver nitrate solution. In the presence of Tollen’s reagent, acetaldehyde is oxidized to acetate ion. Silver nitrate is reduced to silver metal. A black ring of silver is formed in the test tube. This black ring is called a silver mirror.
Acetic acid does not react with Tollen’s reagent.

Note: It is possible to distinguish two compounds by using appropriate reagent. This is possible because two compounds contain different functional groups that react differently with appropriate reagent.