Which anion will produce a colorless, odorless gas when hydrochloric acid (HCl) is added to its solid or solution?

• A. sulfite (SO_3^{2-})
• B. carbonate (CO_3^{2-})
• C. sulfate (SO_4^{2-})
• D. chloride (Cl^-)

Answer: (B)

Verified step by step guidance

1. Identify the possible reactions between hydrochloric acid (HCl) and each anion: sulfite (SO_3^{2-}), carbonate (CO_3^{2-}), sulfate (SO_4^{2-}), and chloride (Cl^-).
2. Recall that when HCl reacts with carbonate ions (CO_3^{2-}), it produces carbon dioxide gas (CO_2), which is colorless and odorless, along with water and dissolved chloride ions. The reaction is: \(\mathrm{CO_3^{2-} + 2HCl \rightarrow CO_2 (g) + H_2O + 2Cl^-}\).
3. Consider the reaction of HCl with sulfite ions (SO_3^{2-}), which produces sulfur dioxide gas (SO_2), a gas that has a distinct pungent odor and is not colorless and odorless.
4. Note that sulfate ions (SO_4^{2-}) generally do not react with HCl to produce any gas, and chloride ions (Cl^-) are the conjugate base of HCl and do not produce gas upon reaction with HCl.
5. Conclude that the anion producing a colorless, odorless gas (CO_2) upon reaction with HCl is the carbonate ion (CO_3^{2-}).