Which acid is used in the sulfite test to release carbon dioxide?

• A. Hydrochloric acid
• B. Nitric acid
• C. Sulfuric acid
• D. Acetic acid

Answer: (A)

The key idea is that carbon dioxide is released when an acid reacts with a carbonate present in the sample. In the sulfite test, you want a strong, non-oxidizing acid to provide the H+ needed to drive the carbonate-to-CO2 reaction without bringing in other side reactions that could confuse the test. Hydrochloric acid fits this role well: it reacts with carbonate like this to give CO2, water, and salt (for example, Na2CO3 + 2 HCl → 2 NaCl + CO2 + H2O). It’s readily available, strong enough to release CO2 quickly, and doesn’t introduce oxidizing species that could alter sulfite chemistry.

The other acids are less ideal here. Nitric acid is a strong oxidizer, which could change sulfite-containing substances and complicate the result. Acetic acid is a weak acid and would release CO2 much more slowly, making the test less reliable. Concentrated sulfuric acid can be harsh and may lead to dehydration or other side reactions rather than a clean CO2 release.