91影视

The activity coefficient $\mathit{纬}$measures the deviation of behavior from ideality,rapidly decreases as ionic strength increases.

With activity coefficients for $\mathrm{HA},{\mathrm{A}}^{-}\mathrm{and}{\mathrm{H}}^{+}$we will predict the value of the quotient forbenzoic acid.

The observed quotient from task is $0.63卤0.03$

The equilibrium constant is given as:

$$\begin{gathered} \mathrm{贬础謴}{\mathrm{H}}^{+}+{\mathrm{A}}^{-} \\ {\mathrm{k}}_{\mathrm{a}}=\frac{\left[{\mathrm{H}}^{+}\right]\mathrm{纬}\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{A}}^{-}\right]\mathrm{y}\left({\mathrm{A}}^{-}\right)}{\left[\mathrm{HA}\right]\mathrm{纬}\left(\mathrm{HA}\right)} \end{gathered}$$

From Pg166 Table 8-1 we can see that $\mathrm{纬}\left({\mathrm{H}}^{+}\right)=0.83\mathrm{and}\mathrm{纬}\left({\mathrm{A}}^{-}\right)=0.80\mathrm{when}0.1\mathrm{M}$

For HA we estimate the following:

$$\begin{gathered} \log \mathrm{纬}\left(\mathrm{HA}\right)=\mathrm{办渭}=0.2脳0.1=0.02 \\ \mathrm{纬}\left(\mathrm{HA}\right)={10}^{0.02}=1.05 \end{gathered}$$

First we will consider the (ionic strength $\mathrm{渭}=0.1\mathrm{M}$)

role="math" localid="1654918428253" $$\begin{gathered} {\mathrm{k}}_{\mathrm{a}}=\frac{\left[{\mathrm{H}}^{+}\right]\left(0.83\right)\left[{\mathrm{A}}^{-}\right]\left(0.80\right)}{\left[\mathrm{HA}\right]\left(1.05\right)}鈬�0.63脳\frac{\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{A}}^{-}\right]}{\left[\mathrm{HA}\right]} \\ =\frac{{\mathrm{k}}_{\mathrm{a}}}{0.63} \end{gathered}$$

Next we will consider the (ionic strength $\mathrm{渭}=0\mathrm{M}$)

$$\begin{gathered} {\mathrm{k}}_{\mathrm{a}}=\frac{\left[{\mathrm{H}}^{+}\right]\left(1\right)\left[{\mathrm{A}}^{-}\right]\left(1\right)}{\left[\mathrm{HA}\right]\left(1\right)}鈬�\frac{\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{A}}^{-}\right]}{\left[\mathrm{HA}\right]} \\ ={\mathrm{k}}_{\mathrm{a}} \end{gathered}$$

consider that when ionic strength$\mathrm{渭}=0\mathrm{M}$ the activities are all 1

Finally, we will take the two values and put them into theconcentration quotient equationgiven in the task.

$$\begin{gathered} =\frac{{\mathrm{k}}_{\mathrm{a}}}{{\mathrm{k}}_{\mathrm{a}}/0.63} \\ =0.63 \end{gathered}$$

Therefore, the predicted value of the concentration quotient is 0.63