MCAT General Chemistry Question 232: Answer and Explanation

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Question: 232

1. The pH of a CH₃COOH solution is < 7 because when this compound is added to water:

A. CH₃COOH donates H⁺, making [H⁺] > [OH^-].
B. CH₃COOH loses OH^-, making [H⁺] < [OH^-].
C. CH₃COO^- deprotonates H₂O, increasing [OH^-].
D. CH₃COOH dissociation increases [H⁺], thereby increasing K_w.

Correct Answer: A

Explanation:

A CH₃COOH is acetic acid, a common organic, carboxylic acid. It will dissociate in water to produce H⁺ and CH₃COO^-, eliminating choice B. An acidic solution (pH < 7) has more H⁺ ions in solution than OH^- ions, making choice A the best answer. Choice C can be eliminated because if [OH^-] were to increase, the pH of the solution would be greater than 7, rather than less than 7. Choice D can be eliminated because the only thing that changes the value of K_w, or any equilibrium constant, is temperature.

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