Question

A solution of 1 molal concentration of a solute will have maximum boiling point elevation when solvent is:
(A) Ethyl alcohol
(B) Acetone
(C) Benzene
(D) Chloroform

Answer 1

Hint: The vapor pressure of liquid increases with an increase of temperature and boils at the temperature at which vapor pressure is equal to the atmospheric pressure. Boiling point elevation is a colligative property of matter, which depends on the solute-to-solvent ratio but not on the identity of the solution.

Complete step by step answer:
Boiling point elevation is defined as the increase in the boiling point of the solvent when adding a solute. When a non-volatile solute is added to the solvent, the boiling point of the solvent increases than the pure solvent.
For example, the boiling point of water increases by adding sodium chloride to pure water.
The elevation of the boiling point of a solution depends on the amount of solute added to the solvent.
Let ${{T}^{o}}_{b}$ be the pure solvent boiling point and ${{T}_{b}}$ the boiling point of the solution. Then the increase in the boiling point,
$\Delta {{T}_{b}}={{T}_{b}}-{{T}_{b}}^{0}$
$\Delta {{T}_{b}}$ is known as the elevation of the boiling point, which is directly proportional to the molal concentration of the solute in a solution.
$\Delta {{T}_{b}}\propto m$
$\Delta {{T}_{b}}={{K}_{b}}m$, where ${{K}_{b}}$ is called molal elevation constant.
The ${{K}_{b}}$value of ethanol = ${{1.22}^{0}}C/mol/Kg$
The ${{K}_{b}}$ Value of acetone = ${{1.67}^{0}}C/mol/Kg$
The ${{K}_{b}}$ value of benzene = ${{2.26}^{0}}C/mol/Kg$
The ${{K}_{b}}$ value of chloroform = ${{3.88}^{0}}C/mol/Kg$
Hence, a solution of 1 molal concentration of a solute will have maximum boiling point elevation when the solvent is chloroform.
So, the correct answer is “Option D”.

Note: The properties depend upon the amount of solute particles regardless of nature relative to the amount of particles present within the solution, are called colligative properties. Those are relative lowering of vapour pressure of solvent, depression of freezing point of the solvent, elevation of boiling point of solvent, and osmotic pressure of the solution.