Question

Ethyl alcohol $\left( {{C_2}{H_5}OH} \right)$ has higher boiling point than dimethyl ether $\left( {C{H_3} - O - C{H_3}} \right)$ although the molecular weight of both are same due to:
a.) Intramolecular H-bonding
b.) Intermolecular H-bonding
c.) Dipole moment
d.) Lattice enthalpy

Answer 1

Hint: This question is of boiling point, therefore we must understand the intermolecular force and bond first which break during the boiling process. For boiling anything we need to break the intermolecular bond of the compound, in simple language we can say that the force by which the atoms or molecules are held together.

Complete step by step solution: As we know that the hydroxyl group is present as a functional group in ethyl alcohol. Hydroxyl groups are polar in nature. The OH group of the ethyl alcohol attracts the shared electron pair of OH bond towards itself. The functional group OH acquires a partial negative charge and the hydrogen atom acquires a positive charge. The negative oxygen atom of one molecule attracts the hydrogen atom of the other molecule. The interaction between OH bonds of the molecules is known as hydrogen bonding. Due to the presence of hydrogen bonding in the molecules of the alcohol, the molecules of alcohol are held together.
Apart from the energy required to break the bond, more energy is required to break the hydrogen bonding of the molecules.
While in the case of ether, there is no hydrogen bonding and the intermolecular attraction present is weaker, that is why ether boils at a relatively lower temperature than alcohol.
Hence, ethanol has a higher boiling point than diethyl ether.

Hence, the correct option is C.

Note: In order to solve these types of questions, you need to have concepts about intermolecular forces of attraction such as hydrogen bonding, vander wall forces and more. The relative strength between the bonding forces are Ionic bonds $>$ Hydrogen bonds $>$ Van der waals dipole-dipole interactions $>$ Vander waals dispersion forces.