Question

In a test tube containing a salt, a few drops of dilute \({H2SO4}\) was added, which gave colourless vapours having the smell of vinegar. The vapours turned blue litmus paper red. Identify the correct anion from the following.

• A. Carbonate, \({CO3^{2-}}\)
• B. Sulphite, \({SO3^{2-}}\)
• C. Acetate, \({CH3COO^-}\)
• D. Sulphide, \({S^{2-}}\)

Hint:

Acetate salts give vinegar-smelling acetic acid vapours with dilute sulphuric acid.

Answer 1

The Correct Option is C

Step 1: Observe the gas or vapour produced.  

The question says that colourless vapours are produced. 
These vapours have the smell of vinegar. 

The smell of vinegar is due to acetic acid: $$ CH_3COOH $$ 


Step 2: Reaction of acetate salt with dilute sulphuric acid. 

When an acetate salt reacts with dilute sulphuric acid, acetic acid vapours are produced: $$ CH_3COONa + H_2SO_4 \rightarrow CH_3COOH + NaHSO_4 $$ 


Step 3: Check litmus test. 

The vapours turn blue litmus red, confirming acidic nature. 
Acetic acid is acidic and turns blue litmus red. 


Step 4: Compare with other anions. 

Carbonate gives: $$ CO_2 $$ (odourless) 
Sulphite gives: $$ SO_2 $$ (pungent smell) 
Sulphide gives: $$ H_2S $$ (rotten egg smell) 

Only acetate gives vinegar smell. 

Therefore, the anion is: CH₃COO⁻