Question

Rank the following in order of decreasing surface tension at a given temperature, and explain your ranking: (a) ${\mathbf{CH}}_3\mathbf{OH}$ (b) ${\mathbf{CH}}_3{\mathbf{CH}}_3$(c) ${\mathbf{CH}}_2\mathbf{O}$

Short answer

The decreasing order of surface tension in the following compounds is as follows:

${\mathbf{CH}}_3\mathbf{OH}\mathbf{>}{\mathbf{CH}}_2\mathbf{O}\mathbf{>}{\mathbf{CH}}_3{\mathbf{CH}}_3$.

Step-by-step solution

Surface Tension

Surface tension is the force experienced by the surface molecules due to the unbalanced forces prevailing on the surface.

Bonding interactions

Considering the alcohols, there exist strong intermolecular H-bonding interactions which exert downward force, thus more surface tension. For simple hydrocarbons, there exists a weak intermolecular London dispersion force, thus exerting weak surface tension. The aldehydes do not consist of strong H-bonding because of the absence of a polar H atom.

Effect on surface tension

Thus, considering the above explanation, the surface tension decreasing order is${\mathbf{CH}}_3\mathbf{OH}\mathbf{>}{\mathbf{CH}}_2\mathbf{O}\mathbf{>}{\mathbf{CH}}_3{\mathbf{CH}}_3$.