MCAT General Chemistry Question 139: Answer and Explanation

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Question: 139

4. Which of the following bases is the weakest?

A. KOH
B. NH₃
C. CH₃NH₂
D. Ca(OH)₂

Correct Answer: B

Explanation:

Soluble hydroxides of Group IA and IIA metals are strong bases, eliminating choices (A) and (D). Choices (B) and (C) are both weak bases; however, methylamine contains an alkyl group, which is electron-donating. This increases the electron density on the nitrogen in methylamine, making it a stronger (Lewis) base. Therefore, ammonia is the weakest base.

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