Which of the following best describes the difference between aqueous solutions of a strong acid and a weak acid?

• A. A strong acid solution contains only ions, while a weak acid solution contains both ions and intact acid molecules.
• B. A strong acid solution contains only intact acid molecules, while a weak acid solution contains only ions.
• C. Both strong and weak acid solutions contain only intact acid molecules.
• D. Both strong and weak acid solutions contain only ions.

Answer: (A)

Verified step by step guidance

1. Understand the concept of acid strength: Strong acids completely dissociate in water, meaning they break apart fully into ions, while weak acids only partially dissociate, so both ions and undissociated acid molecules are present in solution.
2. Recall the dissociation behavior of strong acids: For a strong acid HA, the dissociation can be represented as \(\mathrm{HA} \rightarrow \mathrm{H}^+ + \mathrm{A}^-\), and this reaction goes to completion in aqueous solution.
3. Recall the dissociation behavior of weak acids: For a weak acid HA, the dissociation is an equilibrium process, \(\mathrm{HA} \rightleftharpoons \mathrm{H}^+ + \mathrm{A}^-\), meaning some acid molecules remain intact while some dissociate into ions.
4. Compare the composition of the solutions: A strong acid solution contains essentially only \(\mathrm{H}^+\) and \(\mathrm{A}^-\) ions, whereas a weak acid solution contains a mixture of ions and undissociated \(\mathrm{HA}\) molecules.
5. Use this understanding to evaluate the answer choices and identify that the correct description is that a strong acid solution contains only ions, while a weak acid solution contains both ions and intact acid molecules.