Chapter 18, Problem 18.170P

Interpretation Introduction

Interpretation:

${\text{K}}_{\text{a}}$ of a solution has to be calculated for chloroacetic acid when $\text{ 1}\text{.000 m}$ solution of chloroacetic acid freezes at $\text{ -1}\text{.93}$.

Concept introduction:

An equilibrium constant $\left(K\right)$ is the ratio of concentration of products and reactants raised to appropriate stoichiometric coefficient at equlibrium.

For the general acid HA,

  $\text{HA}\left(\text{aq}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{l}\right)\underset{}{\rightleftharpoons }{\text{H}}_{\text{3}}{\text{O}}^{+}\left(\text{aq}\right)+{\text{A}}^{-}\left(\text{aq}\right)$

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

  $K_a=\frac{\left[{\text{H}}_{\text{3}}{\text{O}}^{+}\right]\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$                                                                                                   $\left(1\right)$

An equilibrium constant $\left(K\right)$ with subscript $a$ indicate that it is an equilibrium constant of an acid in water.

Molar mass calculation is given below,

$\Delta T{\text{ = K}}_f\text{ × m}\times i$