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 \(\mathrm{CO}_{3}{\underline{\phantom{xx}}}^{2-}\) and \(\mathrm{HCO}_{3}{\underline{\phantom{xx}}}^{-}\)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 \(0.215 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\).

A 0.968-g sample of impure sodium hydroxide was dissolved in \(200 \mathrm{ml}\). of aqueous solution. A \(20.0-\mathrm{mL}\). portion of this solution was titrated to the stoichiometric point with \(15.8 \mathrm{~mL}\) of \(0.107 \mathrm{M} \mathrm{HCl}\) (aq). What is the percentage purity of the original sample?

A 1.331-g sample of impure barium hydroxide was dissolved in \(250 \mathrm{~mL}\) of aqueous solution. A \(35.0-\mathrm{mL}\). portion of this solution was titrated to the stoichiometric point with \(17.6 \mathrm{~mL}\) of \(0.0935 \mathrm{M} \mathrm{HCl}\) (aq). What is the percentage purity of the original sample?

Calculate the \(\mathrm{pH}\) at each stage in the titration for the addition of \(0.150 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) to \(25.0 \mathrm{~mL}\). of \(0.110 \mathrm{M} \mathrm{Na} \mathrm{OH}(\mathrm{aq})(\mathrm{a})\) initially; (b) after the addition of \(5.0 \mathrm{~mL}\) of acid; (c) after the addition of a further \(5.0 \mathrm{~mL}\); (d) at the stoichiometric point; (e) after the addition of \(5.0 \mathrm{~mL}\) of acid beyond the stoichiometric point; \((f)\) after the addition of \(10 \mathrm{~mL}\). of acid beyond the stoichiometric point.

Calculate the \(\mathrm{pH}\) at each stage in the titration in which \(0.116 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) is added to \(25.0 \mathrm{~mL}\) of \(0.215 \mathrm{M} \mathrm{KOH}(\mathrm{aq})(\mathrm{a})\) initially; (b) after the addition of \(5.0 \mathrm{~mL}\) of acid; (c) after the addition of a further \(5.0 \mathrm{~mL}\); (d) at the stoichiometric point; (e) after the addition of \(5.0 \mathrm{~mL}\) of acid beyond the stoichiometric point; \((f)\) after the addition of \(10 \mathrm{~mL}\) of acid beyond the stoichiometric point.

\(\mathrm{~A} 30.0-\mathrm{mL}\) sample of \(0.20 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}(\mathrm{aq})\) solution is titrated with \(0.30 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\). (a) What is the initial \(\mathrm{pH}\) of the \(0.20 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}(\mathrm{aq})\) solution? (b) What is the \(\mathrm{pH}\) after the addition of \(15.0 \mathrm{~mL}\) of \(0.30 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\) ? (c) What volume of \(0.30 \mathrm{M}\) \(\mathrm{KOH}(\mathrm{aq})\) is required to reach halfway to the stoichiometric point? (d) Calculate the \(\mathrm{pH}\) at the halfway point. (e) What volume of \(0.30 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\) is required to reach the stoichiometric point? (f) Calculate the \(\mathrm{pH}\) at the stoichiometric point.

Which indicators could you use for a titration of \(0.20 \mathrm{M}\) acetic acid with \(0.20 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\) : (a) methyl orange; (b) litmus; (c) thymol blue; (d) phenolphthalein? Explain your selections.

Which indicators could you use for a titration of \(0.20 \mathrm{M}\) ammonia with \(0.20 \mathrm{M} \mathrm{HCl}(\mathrm{aq}):\) (a) bromocresol green; (b) methyl red; (c) phenol red; (d) thymol blue? Fxplain your selections.

What volume of \(0.123 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\) must be added to \(125 \mathrm{~mL}\) of \(0.197 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}(\mathrm{aq})\) to reach (a) the first stoichiometric point; (b) the second stoichiometric point?

A 0.164-g sample of phosphorous acid, \(\mathrm{H}_{3} \mathrm{PO}_{3}\), is dissolved in water so that the total volume of the solution is \(50.0 \mathrm{~mL}\). (a) Estimate the \(\mathrm{pH}\) of this solution. (b) Fstimate the \(\mathrm{pH}\) of the solution that results when \(6.50 \mathrm{~mL}\) of \(0.175 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\) is added to the phosphorous acid solution. (c) Fstimate the \(\mathrm{pH}\) of the solution if an additional \(4.93 \mathrm{~mL}\) of \(0.175 \mathrm{M}\) \(\mathrm{NaOH}(\mathrm{aq})\) is added to the solution in part (b).

Determine the \(K_{p}\) for the following sparingly soluble substances, given their molar solubilitics: (a) \(\mathrm{AgBr}, 8.8 \times 10^{-7} \mathrm{~mol} \cdot \mathrm{L}^{-1}\); (b) \(\mathrm{PbCrO}_{4}, 1.3 \times\) \(10^{-7} \mathrm{~mol} \cdot \mathrm{L}^{-1}\); (c) \(\mathrm{Ba}(\mathrm{OH})_{2}, 0.11 \mathrm{~mol} \cdot \mathrm{L}^{-1}\); (d) \(\mathrm{MgF}_{2}\) \(1.2 \times 10^{-3} \mathrm{~mol} \mathrm{~L}^{-1}\).

Determine the \(K_{\text {sp }}\) for the following sparingly soluble compounds, given their molar solubilities: (a) AgI, \(9.1 \times 10^{-9} \mathrm{~mol} \cdot \mathrm{L}^{-1}\); (b) \(\mathrm{Ca}(\mathrm{OH})_{2}\), \(0.011 \mathrm{~mol}-\mathrm{L}^{-1}\); (c) \(\mathrm{Ag}_{3} \mathrm{PO}_{4}, 2.7 \times 10^{-6} \mathrm{~mol}^{-\mathrm{L}}^{-1}\) (d) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}, 5.2 \times 10^{-7} \mathrm{~mol} \cdot \mathrm{L}^{-1}\).

Limestone is composed primarily of calcium carbonate, A \(1.0-\mathrm{mm}^{3}\) chip of limestone was accidentally dropped into a water-filled swimming pool, measuring \(10 \mathrm{~m} \times 7 \mathrm{~m} \times 2 \mathrm{~m}\). Assuming that the carbonate ion does not function as a Bronsted base and that the \(\mathrm{pH}\) of the water is 7 , will the pebble dissolve entirely? The density of calcium carbonate is \(2.71 \mathrm{~g} \cdot \mathrm{cm}^{-3}\).

student finds on the shelf a bottle of a pure silver halide that could be AgCl or Agl. Devclop a simple chemical test that would allow the student to distinguish which compound was in the bottle.

A 20-mL sample of \(0.020 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) was titrated with \(0.035 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\). Calculate the \(\mathrm{pH}\) at the following points in the titration and sketch the \(\mathrm{pH}\) curve: (a) no \(\mathrm{KOH}\) added; (b) \(5.00 \mathrm{~mL}\) of \(\mathrm{KOH}\) (aq) added; (c) an additional \(5.00 \mathrm{~mL}\) of \(\mathrm{KOH}\) (aq) (for a total of \(10.0 \mathrm{~mL}\).) added; (d) another \(5.0 \mathrm{~mL}\) of \(\mathrm{KOH}(\mathrm{aq})\) added; (e) another \(5.00 \mathrm{~mL}\). \(\mathrm{KOH}(\mathrm{aq})\) added. (f) Determine the volume of \(\mathrm{KOH}\) (aq) required to reach the stoichiometric point.

An old bottle labcled "Standardized \(6.0 \mathrm{M}\) \(\mathrm{NaOH}^{\prime \prime}\) was found on the back of a shelf in the stockroom. Over time, some of the NaOH had reacted with the glass and the solution was no longer \(6.0 \mathrm{M}\). To determine its purity, \(5.0 \mathrm{~mL}\) of the solution was diluted to \(100 \mathrm{ml}\). and titrated to the stoichiometric point with 11.8 mL. of \(2.05 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\). What is the molarity of the sodium hydroxide solution?

The narcotic cocaine is a weak base wirh \(\mathrm{p} K_{\mathrm{b}}=5.59\). Calculate the ratio of the concentration of cocaine and its conjugate acid in a solution of \(\mathrm{pH}=8.00\).

Novocaine, which is used by dentists as a local anesthetic, is a weak base with \(\mathrm{pK}_{\mathrm{b}}=5.05\). Blood has a pH of \(7.4\). What is the ratio of concentrations of Novocaine to its conjugate acid in the bloodstream?

Will \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) precipitate from a solution formed from a mixture of \(100 \mathrm{~mL}\) of \(1.0 \times 10^{-4} \mathrm{M}\) \(\mathrm{AgNO}_{3}(\) aq \()\) and \(100 \mathrm{~mL}\) of \(1.0 \times 10^{-4} \mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{aq})\) ?

(a) Estimate the \(\mathrm{pH}\) of the solution that results when we add \(25.0 \mathrm{~mL}\) of \(0.150 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\) to \(25.0 \mathrm{~mL}\) of \(0.125 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{3}\) (aq). (b) If we add an additional \(20.0 \mathrm{~mL}\) of the \(\mathrm{NaOH}(\mathrm{aq})\) solution, what would you predict the pH of the resulting solution to be?