Multiple Choice
What is the vapor pressure of a 45.0% solution of glucose (C6H12O6) at a particular temperature, given that the vapor pressure of pure water at that temperature is 486 mm Hg?
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14. Solutions
Vapor Pressure Lowering (Raoult's Law)
Multiple Choice
Which of the following liquid substances has the highest vapor pressure at its normal boiling point?
A
Diethyl ether (C_4H_{10}O)
B
Ethanol (C_2H_5OH)
C
Glycerol (C_3H_8O_3)
D
Water (H_2O)
Verified step by step guidance1
Recall that the vapor pressure of a liquid at its normal boiling point is equal to the external pressure, which is typically 1 atm (or 760 mmHg). This means all substances have the same vapor pressure at their own normal boiling points, by definition.
Understand that the question is likely asking which substance has the highest vapor pressure at a given temperature below their boiling points, or which boils at the lowest temperature, indicating higher vapor pressure at lower temperatures.
Compare the normal boiling points of the substances: lower boiling point means higher vapor pressure at a given temperature. Diethyl ether has a lower boiling point than ethanol, water, and glycerol.
Consider the intermolecular forces: Diethyl ether has weaker London dispersion and dipole-dipole forces compared to the strong hydrogen bonding in ethanol, water, and especially glycerol, which leads to higher vapor pressure for diethyl ether at a given temperature.
Conclude that because diethyl ether has the lowest boiling point and weakest intermolecular forces, it exhibits the highest vapor pressure at its normal boiling point compared to the other substances.
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