Chapter 15, Problem 62A

Interpretation Introduction

Interpretation: The given liquids need to be arranged in order of increasing surface tension.

Concept Introduction: Intermolecular forces in liquids are defined as forces between liquid molecules. These forces can be attractive or repulsive depending on the type of bonding between the atoms of molecules of liquids.

Surface tension can be explained as a property of the surface of the liquids/fluids shrinking into the minimum surface area. Thus, it is the energy needed to increase the surface area of the liquid.

It is directly related to intermolecular forces thus, if liquids have stronger intermolecular interactions, there will be greater surface tension.

Explanation of Solution

The given liquids are as follows:

  $\text{water}\left({\text{H}}_{\text{2}}\text{O}\right)$ , hexane $\left({\text{C}}_{\text{6}}{\text{H}}_{\text{14}}\right)$ and ethanol $\left({\text{C}}_2{\text{H}}_6\text{O}\right)$

On comparing the above three liquids, water and ethanol have hydrogen bonding thus, they have higher intermolecular interactions as compared to hexane. Here, hexane molecules only have London Dispersion forces. Therefore, hexane will have minimum intermolecular forces of attraction. On comparing the hydrogen bonding between water and ethanol molecules, water molecules have strong hydrogen bonding because in the water there are two partial negative charges on O atom making it more electronegative as compared to the O atom in ethanol.

Thus, the increasing order of intermolecular forces will be:

hexane $\left({\text{C}}_{\text{6}}{\text{H}}_{\text{14}}\right)$ $<$ ethanol $\left({\text{C}}_2{\text{H}}_6\text{O}\right)$ $<$ $\text{water}\left({\text{H}}_{\text{2}}\text{O}\right)$ ,

Since if liquids have stronger intermolecular interactions, there will be greater surface tension. Thus, the order of increasing surface tension will be:

hexane $\left({\text{C}}_{\text{6}}{\text{H}}_{\text{14}}\right)$ $<$ ethanol $\left({\text{C}}_2{\text{H}}_6\text{O}\right)$ $<$ $\text{water}\left({\text{H}}_{\text{2}}\text{O}\right)$ ,