Question

The increasing order of the boiling points for the following compounds is:

{C_2}{H_5}OH\;\;\;{C_2}{H_5}Cl\;\;\;\;{C_2}{H_5}C{H_3}\;\;\;{C_2}{H_5}OC{H_3}\\\ \;\;\;\;\;\left( I \right)\;\;\;\;\;\;\;\;\left( {II} \right)\;\;\;\;\;\;\;\;\;\left( {III} \right)\;\;\;\;\;\;\;\;\;\;\left( {IV} \right) \end{array}$$ A. (III)<(IV)<(II)<(I) B. (II)<(III)<(IV)<(I) C. (III)<(II)<(I)<(IV) D. (IV)<(III)<(I)<(II)

Answer 1

Boiling point is the temperature at which the liquid will start converting into the gaseous state. It is specific for each different molecule. The boiling point is not the colligative property, as it is not dependent on the number of solute particles.

Complete answer
In the given question the polarity of the bond needed to be compared to arrange the molecule in the increasing order.
->In ${C_2}{H_5}OH$, alcohol has a polar bond in which the oxygen is electronegative than hydrogen. It forms more extensive hydrogen bonding than that of other molecules.
->In ${C_2}{H_5}Cl\;\;$, chlorine is electronegative than oxygen in ${C_2}{H_5}OH$ but it does not form H-bonding as seen in between alcohol and water.
->The ester ${C_2}{H_5}OC{H_3}$ is not as polar as that of ${C_2}{H_5}Cl\;$.

Ethanol will have a maximum boiling point due to the existence of hydrogen bonding among molecules and even with water molecules. Next lower boiling point will be that of ${C_2}{H_5}Cl\;$due to dipole-dipole interactions between the molecules, partially oppositely charged molecules will be attracted to each other. The above order is satisfied by the Choice (A). From this choice, it may be concluded that the boiling point of ${C_2}{H_5}C{H_3}$ will be lesser than that of ${C_2}{H_5}OC{H_3}$ because there are no dipole-dipole interactions between the molecules of ${C_2}{H_5}C{H_3}$ nor they have H-bonding.

**Hence, the correct option is (A).

Note: **
Here different types of interactions are important to arrange the molecule as per the boiling point, value need not to be known or need not to be learned.Molecules with similar kind of intermolecular forces are then arranged according to their Molecular weight in order to find the greater boiling point.