Chapter 11

The \(K_{\mathrm{w}}\) for \(2 \mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{OH}^{-}\) changes from \(10^{-14}\) at \(25^{\circ} \mathrm{C}\) to \(9.62 \times 10^{-14}\) at \(60^{\circ} \mathrm{C} .\) What is \(\mathrm{pH}\) of water at \(60^{\circ} \mathrm{C} ?\) What happens to its neutrality?

Calculate the \(\mathrm{pH}\) of a solution of given mixtures; (a) \(\left(4 \mathrm{~g} \mathrm{CH}_{3} \mathrm{COOH}+6 \mathrm{~g} \mathrm{CH}_{3} \mathrm{COONa}\right)\) in \(100 \mathrm{~mL}\) of mixture; \(K_{\mathrm{a}}\) for \(\mathrm{CH}_{3} \mathrm{COOH}=1.8 \times 10^{-5}\) (b) \(5 \mathrm{~mL}\) of \(0.1 \mathrm{M} \mathrm{MOH}+250 \mathrm{~mL}\) of \(0.1 \mathrm{M} \mathrm{MCl}\); \(K_{\mathrm{a}}\) for \(M \mathrm{OH}=1.8 \times 10^{-5}\) (c) \(\left(0.25\right.\) mole of \(\mathrm{CH}_{3} \mathrm{COOH}+0.35\) mole of \(\mathrm{CH}_{3} \mathrm{COONa}\) ) in \(500 \mathrm{ml}\) mixture; \(K_{\text {a }}\) for \(\mathrm{CH}_{3} \mathrm{COOH}=3.6 \times 10^{-4}\)

$$ \begin{aligned} &\text { How many mole of } \mathrm{N} \mathrm{H}_{4} \mathrm{Cl} \text { must be added to one litre of } 1.0 \mathrm{M} \mathrm{NH}_{4} \mathrm{OH}\\\ &\text { to have a buffer of } \mathrm{pH}=9 . K_{\mathrm{NH}_{4} \mathrm{OH}}=1.8 \times 10^{-5} ? \end{aligned} $$

Cilculate the \(\mathrm{pH}\) of the resultant mixtures : (ii) \(10 \mathrm{ml}\). of \(0.2 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}+25 \mathrm{~mL}\) of \(0.1 \mathrm{MHCl}\), (b) \(10 \mathrm{ml}\). of \(0.01 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}+10 \mathrm{~mL}\) of \(0.01 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}\), (c) \(10 \mathrm{ml}\) of \(0.1 \mathrm{MH}_{2} \mathrm{SO}_{4}+10 \mathrm{~mL}\) of \(0.1 \mathrm{M} \mathrm{KOH}\).

Benzoic acid is monobasic and when \(1.22 \mathrm{~g}\) of its pure sample after dissolution in distilled water is titrated against a base it uses \(50 \mathrm{~mL}\) of 0.2 \(\mathrm{M} \mathrm{NaOH}\). Calculate the molar mass of benz?ic acid.

Calculate the \(\mathrm{pH}\) of \(0.05 \mathrm{M}\) sodium acetate solution if the \(p K_{a}\) of acetic acid is \(4.74\)

The \(p K_{a}\) of acetic acid and \(p K_{b}\) of ammonium hydroxide are \(4.70\) and \(4.75\) respectively. Calculate the hydrolysis constant of ammonium acetate at \(298 \mathrm{~K}\) and also the degree of hydrolysis and \(\mathrm{pH}\) of its (a) \(0.01 M\) and (b) \(0.04 \mathrm{M}\) solutions.

The solubility of \(\mathrm{Sr}(\mathrm{OH})_{2}\) at \(298 \mathrm{~K}\) is \(19.23 \mathrm{~g} / \mathrm{L}\) of solution. Calculate the concentrations of strontium and hydroxyl ions and the \(\mathrm{pH}\) of the solution.