Chapter 6, Problem 6.69P

Interpretation Introduction

Interpretation:

The mass of methanol needed per 1000 g of water for an aqueous solution to stay liquid at $-20{}^{\circ }\text{C}$

Concept Introduction:

The freezing point depression can be related to the total molality of the solution and the normal freezing point of the solvent.

In this specific case the solvent is water, therefore, the freezing point of water as well as the depression constant must be known.

$T_{\text{F}-m\text{i}\text{X}}=T_{\text{F}-pur\text{e}}-K_{\text{F}}m\text{i}$ …… (1).

Where,

$\begin{array}{l}{T}_{\text{F}-m\text{i}\text{X}}=\text{new}\text{freezing}\text{point}\\ T_{\text{F}-pur\text{e}}=\text{pure}\text{freezing}\text{point}\\ K_{\text{F}}=\text{freezing}\text{point}\text{depression}\text{constant}\\ m=\text{molality}\\ \text{i}=\text{number}\text{of}\text{species}\end{array}$.