Chapter 14, Problem 30A

Interpretation Introduction

Interpretation:

After finding out the more volatile compound and the compound with high boiling point, the reason has to be explained.

Concept Introduction:

The intermolecular forces of attraction can be H-bonding, dipole-dipole interaction and London dispersion forces. When the intermolecular forces of attraction between two molecules are very high, the vapor pressure of the compound will be lower. Thus the compound will be less volatile. When the intermolecular forces of attraction between two molecules are low, the vapor pressure of the compound will be high. Thus the compound will be more volatile.

The boiling point of a compound also depends on intermolecular attractive forces between two molecules.

Answer to Problem 30A

• Dimethyl ether is more volatile.
• The boiling point of ethanol is much higher than dimethyl ether.

Explanation of Solution

(1) The intermolecular forces of attraction between ethanol molecules are very high due to the presence of strong hydrogen bonding between oxygen and hydrogen atoms. Ethyl alcohol molecules also exhibit dipole-dipole interaction and London dispersion forces. But there is no such interactions present between dimethyl ether molecules. As intermolecular forces of attraction are weaker in dimethyl ether, the vapor pressure will be high. Therefore dimethyl ether is more volatile.

(2) The boiling point of ethanol is much higher than dimethyl ether due to the presence of strong intermolecular hydrogen bonding between ethyl alcohol molecules through oxygen and hydrogen atoms. Thus many ethanol molecules bind to each other. Therefore the boiling point of ethanol is much higher.