MCAT General Chemistry Question 229: Answer and Explanation

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Question: 229

7. The water solubility of MgSO4 is approximately 25 g/100 mL at 20°C. Compared to a 0.25 g/mL solution of MgSO4 prepared at 20°C, a 0.25 g/mL solution prepared at 37°C will:

  • A. dissolve faster and have the same concentration of ions in solution.
  • B. dissolve faster and have a higher concentration of ions in solution.
  • C. dissolve slower and have a lower concentration of ions in solution.
  • D. dissolve slower and have the same concentration of ions in solution.

Correct Answer: A

Explanation:

A This is a two-by-two problem. First, consider rate. Any time temperature is increased, the reaction kinetics increase. In this case, the salt will dissolve faster, eliminating choices C and D. An increase in temperature generally causes an increase in the solubility of solids in liquids. However, both solutions contain the same amount of MgSO4 that does not exceed the maximum solubility at either temperature. Therefore, the concentrations of ions will be the same, eliminating choice B.

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