The boiling point of water is 100C, ethanol is 78C and carbon tetrachlorides is 76C. Which describes the strength of the forces between the molecules of water ethanol and carbon tetrachloride?

Question

The forces between them are not a good predictor of boiling points of different substances
The forces between molecules of water, ethanol and carbon tetrachloride are very similar
The forces between water molecules are greater than those of ethanol and carbon tetrachloride molecules
The forces between molecules are greatest for carbon tetrachloride and ethanol molecules but much lower for water molecules

Answer 1

To analyze the boiling points and the strength of intermolecular forces among water, ethanol, and carbon tetrachloride (CCl₄), we can look at the types of intermolecular forces present in each substance.

1. Water (H₂O): Water has strong hydrogen bonding due to the highly polar O-H bonds and its bent molecular shape. This results in strong attractive forces between water molecules, which significantly raises the boiling point.

2. Ethanol (C₂H₅OH): Ethanol also has hydrogen bonding because of the O-H group, but it is less significant than in water due to the presence of a larger non-polar hydrocarbon (ethyl) portion. Therefore, while ethanol has hydrogen bonding, it is not as strong as that in water.

3. Carbon Tetrachloride (CCl₄): CCl₄ is a non-polar molecule and primarily exhibits London dispersion forces, which are much weaker than hydrogen bonds. As a result, its boiling point is lower than that of both ethanol and water.

Based on this information, the statement that best describes the strength of the forces between the molecules is:

"The forces between water molecules are greater than those of ethanol and carbon tetrachloride molecules."

This highlights the strong hydrogen bonding in water compared to the hydrogen bonding in ethanol and the much weaker dispersion forces in carbon tetrachloride.