MCAT General Chemistry Question 289: Answer and Explanation

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Question: 289

2. If CO₂ gas is bubbled continuously in a beaker of water to form carbonic acid, which of the following would be true?

I. Addition of carbonic anhydrase will increase the K_eq of the reaction.

II. Carbonic acid will increase in concentration until K_eq is reached.

III. Addition of bicarbonate will increase the pH of the system.

A. I only
B. II only
C. III only
D. II and III

Correct Answer: D

Explanation:

D Addition of a catalyst (such as the enzyme carbonic anhydrase) will simply increase the rate of a reaction. It plays no role in shifting the equilibrium, or changing the equilibrium constant making Item I false (eliminate choice A). As carbon dioxide is bubbled through, carbonic acid will form until its equilibrium concentration is attained, making Item II valid (eliminate choice C). Finally, addition of bicarbonate will shift the carbonic acid equilibrium to the reactant side, consuming H⁺ in the process. Since the concentration of H⁺ will decrease, pH will increase, making Item III valid (eliminate choice B).

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