Chapter 12, Problem 89RQ

Interpretation Introduction

Interpretation:

The vapor pressure of water at $20°\text{C}$ is $\text{17}\text{.5 torr}$. At that temperature, the vapor pressure of the solution, made by dissolving $23\text{ g}$ of NaCl in $0.100\text{ kg}$ of water, is to be determined.

Concept Information:

According to Raoult's law:

$\Delta P=X_{solvent}{P}^{\circ }$

Here, $X_{solvent}$ is the mole fraction of solvent, $P^{\circ }$ is the partial pressure of pure solution and $\Delta P$ is the change in vapour pressure.

Dalton law states that,

$P_{\text{sol}}=X_A{P}_A+X_B{P}_B$

Here $X_A,X_B$ are the mole fraction of compounds, $P_A,P_B$ are the partial pressures and $P_{\text{sol}}$ is the vapor pressure of the solution.

The number of moles of solute is calculated by dividing the mass of solute by the molar mass of the solute.

$n=\frac{m}{M_{\text{w}}}$

Here, $m$ is the mass of solute and $M_{\text{w}}$ is the molar mass of the solute.

Mole fraction can be calculated as follows:

$X=\frac{n_{\text{a}}}{n_{\text{a}}+n_{\text{b}}}$

Here, $n_{\text{a}},n_{\text{b}}$ are moles of compounds a and b.