MCAT General Chemistry Question 228: Answer and Explanation

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Question: 228

6. Which of the following salts is least soluble in water?

  • A. PbI2 (Ksp = 7.9 × 10-9)
  • B. Mg(OH)2 (Ksp = 6.3 × 10-10)
  • C. Zn(IO3)2 (Ksp = 3.9 × 10-6)
  • D. SrF2 (Ksp = 2.6 × 10-9)

Correct Answer: B

Explanation:

B All of the compounds are composed of one cation and two anions, so comparing Ksp values will give relative solubility. Since the question asks for an extreme, the middle values of the variable cannot be correct, eliminating choices A and D. The compound with the lowest Ksp value will have the lowest solubility because for all the compounds, Ksp = [cation][anion]2. Therefore, choice B is correct.

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