MCAT General Chemistry Question 283: Answer and Explanation

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Question: 283

2. As the ground temperature surrounding a cave increases, stalactite and stalagmite growth is found to decrease. What is the best explanation for this?

  • A. Increased heat causes CaCO3 to melt.
  • B. Formation of stalactites and stalagmites is endothermic.
  • C. Increasing temperature decreases the aqueous solubility of CaCO3.
  • D. The concentration of CO2(g) in water increases as temperature increases.

Correct Answer: C

Explanation:

C This question is best answered by Process of Elimination, because the answer is unexpected. CaCO3 is an ionic compound with a melting point greater than 800°C, making choice A unlikely. If formation of stalactites and stalagmites were endothermic, increased temperature would favor their formation, eliminating choice B. Increased temperature decreases the concentration of dissolved gases in liquids, eliminating choice D. CaCO3 is one of the exceptions to general solubility rules because its solubility in water actually decreases with increasing temperature. If less CaCO3 gets dissolved, less will be available to precipitate in the cave as a stalactite or stalagmite.

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