MCAT General Chemistry Question 88: Answer and Explanation

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Question: 88

13. Compound A has a K_a (equilibrium constant of acid dissociation) of approximately 10^–4. Which of the following compounds is most likely to react with a solution of compound A?

A. HNO₃
B. NO₂
C. NH₃
D. N₂O₅

Correct Answer: C

Explanation:

K_a is equal to the ratio of products to reactants, with each species raised to its stoichiometric coefficient. A compound with a K_a greater than 10^-7 contains more H⁺ cations than HA^- anions at equilibrium, which makes it an acid. This means that the compound in question is likely to react with a compound that is basic. Of the four answer choices, NH₃ is the only base.

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