Question

Rank the compounds in Problem 12.62 in order of increasing viscosity at a given temperature; explain your ranking.

Short answer

The increasing order of viscosity in the following compounds is as follows:

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

Step-by-step solution

Viscosity

The viscosity of a fluid is the resistance to any movement experienced by the liquid molecules against any external force applied.

Bonding interactions

Considering the alcohols, there exist strong intermolecular H-bonding interactions which exert downward force, thus more viscosity. For simple hydrocarbons, there exists a weak intermolecular London dispersion force, thus exerting less viscosity. 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${\mathbf{CH}}_3{\mathbf{CH}}_3\mathbf{<}{\mathbf{CH}}_2\mathbf{O}\mathbf{<}{\mathbf{CH}}_3\mathbf{OH}$.