Question

Chemical formula of potassium metabisulphite is

• A. K_2S_2O_5
• B. K_2S_2O_7
• C. K_3S_2O_5
• D. K_3S_3O_7

Hint:

$\text{K}_2\text{S}_2\text{O}_5$ releases approximately $57\%$ by weight of active sulfur dioxide ($\text{SO}_2$) upon acidification.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Sulfiting agents are widely used chemical preservatives and antioxidants in fruit products and wines.

Step 2: Detailed Explanation:
Potassium metabisulphite (potassium pyrosulphite, food additive E224) has the molecular chemical formula $\text{K}_2\text{S}_2\text{O}_5$.
In acidic food solutions, it dissolves and hydrolyzes to release antimicrobial and antioxidant sulfur dioxide ($\text{SO}_2$) and bisulfite ions ($\text{HSO}_3^-$):
\[\text{K}_2\text{S}_2\text{O}_5 + \text{H}_2\text{O} \rightleftharpoons 2\text{K}^+ + 2\text{HSO}_3^-\]

Step 3: Final Answer:
Hence, the chemical formula of potassium metabisulphite is $\text{K}_2\text{S}_2\text{O}_5$.