Chapter 11

Explain what happens to (a) the \(\mathrm{pH}\) of a phosphoric acid solution after the addition of solid sodium dihydrogen phosphate; (b) the percentage deprotonation of HCN in a hydrocyanic acid solution after the addition of hydrobromic acid; (c) the concentration of \(\mathrm{H}_{3} \mathrm{O}^{+}\)ions when pyridinium chloride is added to a pyridine solution.

Determine the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of (a) a solution that is \(0.40 \mathrm{M} \mathrm{NaHSO}_{4}(\mathrm{aq})\) and \(0.080 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})\); (b) a solution that is \(0.40 \mathrm{M} \mathrm{NaHSO}_{4}(\mathrm{aq})\) and \(0.20 \mathrm{M}\) \(\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq}) ;\) (c) a solution that is \(0.40 \mathrm{M} \mathrm{NaHSO}_{4}(\mathrm{aq})\) and \(0.40 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})\).

Calculate the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of (a) a solution that is \(0.17 \mathrm{M} \mathrm{Na}_{2} \mathrm{HPO}_{4}\) (aq) and \(0.25 \mathrm{M} \mathrm{Na}_{3} \mathrm{PO}_{4}\) (aq); (b) a solution that is \(0.66 \mathrm{M} \mathrm{Na}_{2} \mathrm{HPO}_{4}(\mathrm{aq})\) and \(0.42 \mathrm{M}\) \(\mathrm{Na}_{3} \mathrm{PO}_{4}(\mathrm{aq}) ;\) (c) a solution that is \(0.12 \mathrm{M} \mathrm{Na}_{2} \mathrm{HPO}_{4}(\mathrm{aq})\) and \(0.12 \mathrm{M} \mathrm{Na}_{3} \mathrm{PO}_{4}(\mathrm{aq})\).

Predict the \(\mathrm{pH}\) region in which each of the following buffers will be effective, assuming equal molarities of the acid and its conjugate base: (a) sodium lactate and lactic acid; (b) sodium benzoate and benzoic acid; (c) potassium hydrogen phosphate and potassium phosphate; (d) potassium hydrogen phosphate and potassium dihydrogen phosphate; (e) hydroxylamine and hydroxylammonium chloride.

Predict the pH region in which each of the following buffers will be effective, assuming equal molarities of the acid and its conjugate base: (a) sodium nitrite and nitrous acid; (b) sodium formate and formic acid; (c) sodium carbonate and sodium hydrogen carbonate; (d) ammonia and ammonium chloride; (c) pyridine and pyridinium chloride.

(a) What must be the ratio of the concentrations of \(\mathrm{CO}_{3}{ }^{2-}\) and \(\mathrm{HCO}_{3}{ }^{-}\)ions in a buffer solution having a \(\mathrm{pH}\) of \(11 . \mathrm{O}\) ? (b) What mass of \(\mathrm{K}_{2} \mathrm{CO}_{3}\) must be added to \(1.00 \mathrm{~L}\) of \(0.100 \mathrm{M} \mathrm{KHCO}_{3}(\mathrm{aq})\) to prepare a buffer solution with a pH of \(11.0\) ? (c) What mass of \(\mathrm{KHCO}_{3}\) must be added to \(1.00 \mathrm{~L}\) of \(0.100 \mathrm{M} \mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})\) to prepare a buffer solution with a pH of \(11.0\) ? (d) What volume of \(0.200 \mathrm{M} \mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})\) must be added to \(100 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{KHCO}_{3}(\mathrm{aq})\) to prepare a buffer solution with a pH of \(11.0\) ?

Sketch reasonably accurately the \(\mathrm{pH}\) curve for the titration of \(20.0 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) with \(0.20 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\). Mark on the curve (a) the initial \(\mathrm{pH}\); (b) the pH at the stoichiometric point.

Sketch reasonably accurately the \(\mathrm{pH}\) curve for the titration of \(20.0 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}(\mathrm{aq})\) with \(0.20 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\). Mark on the curve (a) the initial \(\mathrm{pH}\); (b) the \(\mathrm{pH}\) at the stoichiometric point.

Calculate the volume of \(0.150 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) required to neutralize (a) one-half and (b) all the hydroxide ions in \(25.0 \mathrm{~mL}\) of \(0.110 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\). (c) What is the molarity of \(\mathrm{Na}^{*}\) ions at the stoichiometric point? (d) Calculate the \(\mathrm{pH}\) of the solution after the addition of \(20.0 \mathrm{~mL}\) of \(0.150 \mathrm{M}\) HClaq) to \(25.0 \mathrm{~mL}\) of \(0.110 \mathrm{M} \mathrm{NaOH}(\mathrm{aq}) .\)

Galculate the volume of \(0.116 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) required to neutralize (a) one-half and (b) all the hydroxide ions in \(25.0 \mathrm{~mL}\) of \(0.215 \mathrm{M} \mathrm{KOH}\) (aq). (c) What is the molarity of \(\mathrm{Cl}^{-}\)ions at the stoichiometric point? (d) Calculate the \(\mathrm{pH}\) of the solution after the addition of \(40.0 \mathrm{~mL}\) of \(0.116 \mathrm{M}\) HCl(aq) to \(25.0 \mathrm{~mL}\) of \(0.215 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\).