Chapter 13.6, Problem 1PPB

Interpretation Introduction

Interpretation:

The mass of ethylene glycolrequired to raise the boiling point to 103.9°Cis to be calculated with the help of mass of water and boiling point of the solution.

Concept introduction:

Molality is defined as the total number of moles present in one kilogram of the solvent.

The mass of the solvent should be in kilograms $\left(\text{kg}\right)$. Calculate molality as follows:

$m=\frac{\text{Moles of solute}}{\text{Mass of solvent}\left(\text{in Kg}\right)}$

$\text{No}\text{. of moles}=\frac{\text{mass}}{\text{molar mass}}$

The temperature at which vapor pressure of a liquid becomes equal to the atmospheric pressure is known as boiling point.

The boiling point elevation is as follows:

$\Delta T_{\text{b}}=m\times K_{\text{b}}$

Here, $\Delta T_{\text{b}}$ is the change in temperature of the boiling point, $m$ is the molality of the solution, and $K_{\text{b}}$ is the boiling point elevation constant for the solvent.

For water:

$K_{\text{b}}=0.52\frac{\text{C}}{m}$

The actual boiling point of the solution is the sum of boiling point of pure water and boiling point elevation $\left(\Delta T_{\text{b}}\right)$:

$T_b=T_b{}^{°}+\Delta T_{\text{b}}$