MCAT General Chemistry Question 47: Answer and Explanation

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Question: 47

2. Which of the following compounds has a formula weight between 74 and 75 grams per mole?

A. KCl
B. C₄H₁₀O
C. MgCl₂
D. BF₃

Correct Answer: A

Explanation:

Of the compounds listed, both choices (B) and (D) are covalent compounds and thus are measured in molecular weights, not formula weights. The formula weight of MgCl₂ is much too high (24.3 amu + 2 × 35.5 amu = 95.3 amu per formula unit), eliminating choice (C). Only KCl fits the criteria (39.1 amu + 35.5 amu = 74.6 amu).

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