12.62P - Chemistry: Molecular Nature Of Matter And Change

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)  ${\mathbf{CH}}_2\mathbf{O}$

Step-by-Step Solution

Answer

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

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

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