Suppose you have two colorless molecular liquids, one boiling at \(-84^{\circ} \mathrm{C}\), the other at \(34{ }^{\circ} \mathrm{C},\) and both at atmospheric pressure. Which of the following statements is correct? For each statement that is not correct, modify the statement so that it is correct. (a) The higher-boiling liquid has greater total intermolecular forces than the lower- boiling liquid. (b) The lower-boiling liquid must consist of nonpolar molecules. (c) The lower-boiling liquid has a lower molecular weight than the higher-boiling liquid. (d) The two liquids have identical vapor pressures at their normal boiling points. (e) \(\mathrm{At}-84{ }^{\circ} \mathrm{C}\) both liquids have vapor pressures of \(760 \mathrm{~mm} \mathrm{Hg}\).

Step by step solution

01

a) Analyzing intermolecular forces of higher and lower-boiling liquids

The statement is correct. The higher-boiling liquid has greater total intermolecular forces than the lower-boiling liquid. This is because stronger intermolecular forces require more energy to break, which corresponds to a higher boiling point.

02

b) Checking if the lower-boiling liquid consists of nonpolar molecules

The statement is not necessarily correct. While it is true that nonpolar molecules tend to have weaker intermolecular forces and thus lower boiling points, it does not imply that the lower-boiling liquid must consist of nonpolar molecules. Corrected statement: The lower-boiling liquid may consist of nonpolar molecules or have weaker intermolecular forces compared to the higher-boiling liquid.

03

c) Comparing molecular weight of lower and higher-boiling liquids

The statement is not necessarily correct. Lower molecular weight can contribute to a lower boiling point, but it is not the sole determining factor. The type of intermolecular forces present also plays a significant role in boiling points. Corrected statement: The lower-boiling liquid may have a lower molecular weight than the higher-boiling liquid, but other factors, like the strength of intermolecular forces, also contribute.

04

d) Comparing vapor pressures of both liquids at their normal boiling points

The statement is incorrect. The vapor pressure of a substance is unique to that substance and depends on temperature. At their normal boiling points, each liquid has a vapor pressure of 1 atmosphere (760 mm Hg), but they have different normal boiling points (-84°C and 34°C). Corrected statement: The two liquids have vapor pressures of 1 atmosphere (760 mm Hg) at their respective normal boiling points.

05

e) Comparing vapor pressures of both liquids at -84°C

The statement is incorrect. The vapor pressure of a substance depends on the temperature, and it is different for different substances. Only the liquid with a boiling point of -84°C will have a vapor pressure of 760 mm Hg at this temperature. Corrected statement: At -84°C, the lower-boiling liquid has a vapor pressure of 760 mm Hg, while the higher-boiling liquid has a lower vapor pressure.

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