Question 7.15: What is the activity coefficient of copper in a solution of ......

Copper sulphate is a 2:2 electrolyte so, from Table 7.5, the ionic strength I is four times its concentration. We say I = 4 × 10^{-4}\mathrm{~mol~dm}^{-3}.

Inserting values into Equation (7.33):

\log_{10}\ \gamma_{\pm}=-0.509\ \vert+2\times-2\vert(4\times10^{-4})^{1/2}

\log_{10}\gamma_{\pm}=-2.04\times(2\times10^{-2})

\log_{10}\gamma_{\pm}=-4.07\times10^{-2}

\log_{10}\gamma_{\pm}=-A|z^{+}z^{-}|\sqrt{I}                (7.33)

Taking the anti-log:

\gamma_{\pm}=10^{-0.0407}

\gamma_{\pm}=0.911

We calculate that the perceived concentration is 91 percent of the real concentration.