The molal freezing-point depression constants for benzene and water are 5.12 and 1.86, respectively. When 4.6 g of formic acid (HCOOH) is dissolved in 1.0 kg of benzene, the freezing point is depressed by 0.26°C. When the same amount of formic acid is dissolved in 1.0 kg of water, the freezing point is lowered by 0.19°C. To explain these results, we must assume that

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The molal freezing-point depression constant for benzene is greater than that of water, meaning that the freezing point of benzene is more sensitive to changes in solute concentration. Since the depression of the freezing point of benzene is greater than that of water with the same amount of solute, this suggests that the formic acid molecules are closely associated in benzene (resulting in a larger reduction in the freezing point) but are mostly in a monomeric state in water.

The Molal Freezing-Point Depression Constants for Benzene and Water Are