During the sulfur dioxide test with acidified potassium permanganate, what is observed to happen to the purple permanganate solution?

• A. Remains purple
• B. Turns colorless
• C. Turns blue
• D. Turns yellow

Answer: (B)

In acidified potassium permanganate, permanganate acts as a strong oxidant and is reduced when a reducing agent like sulfur dioxide is present. Sulfur dioxide donates electrons and is oxidized, while MnO4− gains those electrons and is reduced to Mn2+. In acidic solution, Mn2+ is essentially colorless, whereas MnO4− is purple, so the purple solution loses its color as the reaction occurs. That makes the observed change a purple solution turning colorless.