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

To solve this question, let's analyze the chemical reaction and properties given in the question:

1. \({H2SO4}\) is added to a salt solution. This step indicates a reaction where an acid reacts with the salt to possibly release a gas.
2. The gas released has the smell of vinegar and turns blue litmus paper red. This suggests two important observations:
   • The smell of vinegar signifies the presence of acetic acid (ethanoic acid), which hints at an acetate ion.
   • Turning blue litmus paper red confirms that the vapours are acidic.

Based on these observations, we can conclude the following:

• Carbonate ions ( \({CO3^{2-}}\) ) typically react with acids to produce carbon dioxide gas, which does not smell like vinegar or turn litmus red.
• Sulphite ions ( \({SO3^{2-}}\) ) react with acids to form sulfur dioxide, which has a pungent suffocating smell, not resembling vinegar.
• Acetate ions ( \({CH3COO^-}\) ) react with acids to form acetic acid, which indeed smells like vinegar and is acidic enough to turn litmus paper red.
• Sulphide ions ( \({S^{2-}}\) ) produce hydrogen sulfide with acids, which has a characteristic rotten egg smell, distinctly different from vinegar.

Thus, the gas formed must be acetic acid due to the vinegar smell, indicating the presence of acetate ions.

Given the options and the properties observed, the correct anion is Acetate, \({CH3COO^-}\).