To evaluate the statements about hydrochloric acid (HCl) and acetic acid (CH₃COOH), we can use the definitions of strong and weak acids, as well as their dissociation behavior:
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HCl is a strong acid: This means it completely dissociates in solution. Therefore, in a solution of HCl, almost all the acid molecules will release hydrogen ions (H⁺), contributing to a low pH.
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CH₃COOH is a weak acid: This means it only partially dissociates in solution. Therefore, a significant portion of the acetic acid remains in the undissociated form, producing fewer H⁺ ions compared to a strong acid at the same concentration.
Given these definitions, let's assess the provided statements:
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The pH of a solution of hydrochloric acid must be less than the pH of a solution of acetic acid.
- True - Because HCl completely dissociates, it produces a higher concentration of H⁺ ions leading to a lower pH than acetic acid.
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The dissociation constant for hydrochloric acid is greater than the dissociation constant for acetic acid.
- True - HCl has a very large dissociation constant (essentially infinite for practical purposes), indicating complete dissociation, while acetic acid has a smaller dissociation constant (Ka ≈ 1.8 x 10⁻⁵).
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A solution of hydrochloric acid at equilibrium will have a greater concentration of solute than a solution of acetic acid at equilibrium.
- False - The concentration of solute may depend on the specific concentrations used, but both HCl and acetic acid dissociate into H⁺ and their respective anions. At equilibrium, HCl will not have a higher concentration of solute because it completely dissociates.
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If the initial concentration of each acid is the same, then acetic acid will produce more H₃O⁺ ions than hydrochloric acid.
- False - Given that HCl completely dissociates and acetic acid only partially dissociates, HCl will produce more H₃O⁺ ions.
Based on this analysis, the second statement about the dissociation constant is also correct, but the response most directly interpreted as correct in context is:
The pH of a solution of hydrochloric acid must be less than the pH of a solution of acetic acid.
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