MCAT General Chemistry Question 171: Answer and Explanation

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Question: 171

6. Which of the following compounds is LEAST likely to be found in the salt bridge of a galvanic cell?

A. NaCl
B. SO₃
C. MgSO₃
D. NH₄NO₃

Correct Answer: B

Explanation:

Salt bridges contain inert electrolytes. Ionic compounds, such as choices (A), (C), and (D), are known to be strong electrolytes because they completely dissociate in solution. Choice (B) cannot be considered an electrolyte because its atoms are covalently bonded and will not dissociate in aqueous solution. Choices (B) and (C) may appear similar, but there is an important distinction to be made. Choice (C) implies that Mg²⁺ and SO₃^2- are the final, dissociated ionic constituents, while choice (B) implies that neutral SO₃ would have to be dissolved in solution.

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