MCAT General Chemistry Question 194: Answer and Explanation

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Question: 194

5. An electrochemical cell is constructed using two inert electrodes in one chamber with an inert electrolyte. The binary compound ICl is dissolved in the electrolyte, current is applied, and I2 and Cl2 are produced. Which of the following statements is true?

  • A. I > IV > II > III
  • B. II > I > IV > III
  • C. I > III > IV > II
  • D. IV > III > I > II

Correct Answer: A

Explanation:

A When answering ranking questions, it is best to determine the extremes and eliminate answer choices. Of the four molecules, only H2O and H2SO4 are liquids at room temperature, and therefore would have higher boiling points than the two gases. Both experience strong hydrogen bonding, but the H2SO4 molecule is substantially larger, and, aside from this, has more sites to accept H-bonds from surrounding molecules. Therefore, H2SO4 should have the highest boiling point, eliminating answer choices B and D. Both NH3 and CO2 are gases at room temperature. However, NH3 experiences hydrogen bonding, and therefore its boiling point would be higher than CO2, eliminating choice C and making choice A the correct answer.

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