Which acid is classified as a strong acid?

Which acid is classified as a strong acid?

• A. Sulfuric acid
• B. Phosphoric acid
• C. Carbonic acid
• D. Acetic acid

Answer: (A)

The main idea is how completely acids ionize in water. A strong acid almost completely dissociates to release H+ (and its conjugate base) in solution, giving a high hydrogen ion concentration and a very low pH. The other acids listed only partially dissociate, so most of the acid remains as undissociated molecules, and their solutions have much higher pH for a given concentration. Among these options, sulfuric acid is the one that fully ionizes in its first proton, so it behaves as a strong acid in typical introductory chemistry contexts. Phosphoric, carbonic, and acetic acids each dissociate only incompletely in water (they have measurable amounts of unionized acid), classifying them as weak acids.

The main idea is how completely acids ionize in water. A strong acid almost completely dissociates to release H+ (and its conjugate base) in solution, giving a high hydrogen ion concentration and a very low pH. The other acids listed only partially dissociate, so most of the acid remains as undissociated molecules, and their solutions have much higher pH for a given concentration.

Among these options, sulfuric acid is the one that fully ionizes in its first proton, so it behaves as a strong acid in typical introductory chemistry contexts. Phosphoric, carbonic, and acetic acids each dissociate only incompletely in water (they have measurable amounts of unionized acid), classifying them as weak acids.