MCAT General Chemistry Question 292: Answer and Explanation

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Question: 292

5. What is the relationship between the K_a1 value for phosphoric acid and the K_b1 value for dihydrogen phosphate?

A. K_a1 and K_b1 are inversely related through the dissociation constant for water, K_w.
B. K_a1 and K_b1 are directly related through the dissociation constant for water, K_w.
C. The K_a1 is less than the K_b1.
D. There is no relationship between K_a1 and K_b1.

Correct Answer: A

Explanation:

A The relationship between the K_a value of an acid and the K_b value of its conjugate base is through the dissociation constant of water, where K_w = (K_a)(K_b). Therefore, the relationship between K_a1 and K_b1 is K_a1 = K_w/K_b1; an inverse relationship.

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