Chapter 12

Practise interconverting pH values and proton concentrations. Express all values to four significant figures. (a) What is a pH \(7.4\) expressed as \(\left[\mathrm{H}^{+}\right]\)in \(\mathrm{mol} \mathrm{L}^{-1} ?\) (b) What is a pH \(4.1\) expressed as \(\left[\mathrm{H}^{+}\right]\)in mol \(L^{-1} ?\) (c) What is the \(\mathrm{pH}\) of a solution of \(\left[\mathrm{H}^{+}\right]\)at \(2 \times 10^{-5} \mathrm{~mol} \mathrm{~L}^{-1} ?\) (d) What is the pH of a solution of \(\left[\mathrm{H}^{+}\right]\)at \(2 \times 10^{-12.5} \mathrm{~mol} \mathrm{~L}^{-1} ?\)

Practise using the Henderson-Hasselbalch equation. What are the relative proportions of the deprotonated \(\left(A^{-}\right)\)and protonated (HA) forms of each substance at the following \(\mathrm{pH}\) values: (a) ethanoic acid \(\left(\mathrm{p} K_{\mathrm{a}}=4.8\right.\) ) for use in an experiment at pH 3.8; (b) boric acid \(\left(\mathrm{p} K_{\mathrm{a}}=9.2\right)\) for use in an experiment at pH 9.5; (a) HEPES \(\left(p K_{a}=7.5\right)\) for use in an experiment at \(\mathrm{pH}\) 8.1?