Q12.58P - Chemistry: Molecular Nature Of Matter And Change

Question

Why does an aqueous solution of ethanol ( ${\mathbf{CH}}_3{\mathbf{CH}}_2\mathbf{OH}$) have a lower surface tension than water?

Step-by-Step Solution

Answer

The aqueous solution of ethanol has a lower surface tension than water because of the non-polar hydrocarbon chain present in ethanol. This reduces the H-bonding within the molecules, thus the force of attraction is comparatively lower.

Step 1: Surface Tension

The surface tension is a phenomenon in which the surface area of the liquid decreases because of the unbalanced forces of attraction present on the surface than in the bulk.

 

Step 2: H-bonding interactions

Ethanol has a hydrocarbon chain present along with the –OH group, which reduces the H-bonding interactions present in the aqueous solution of ethanol. These non-polar chains when present on the surface of the liquid involves more weak London dispersion forces than the strong H-bonding interactions.

Step 3: Lowering in boiling point

Hence, due to the low relative strength of interactions in an aqueous solution of ethanol than in water, the former has lower surface tension than water.