Chapter 16

Write the formula and give the name of the conjugate base of each of the following acids. (a) HCN (b) \(\mathrm{HSO}_{4}^{-}\) (c) HF

Write the formula and give the name of the conjugate acid of each of the following bases. (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{HCO}_{3}^{-}\) (c) \(\mathrm{Br}^{-}\)

What are the products of each of the following acid-base reactions? Indicate the acid and its conjugate base and the base and its conjugate acid. (a) \(\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (b) \(\mathrm{HSO}_{4}^{-}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (c) \(\mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{F}^{-} \rightarrow\)

What are the products of each of the following acid-base reactions? Indicate the acid and its conjugate base and the base and its conjugate acid. (a) \(\mathrm{HClO}_{4}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (b) \(\mathrm{NH}_{4}^{+}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) (c) \(\mathrm{HCO}_{3}^{-}+\mathrm{OH}^{-} \rightarrow\)

Write balanced equations showing how the hydrogen oxalate ion, \(\mathrm{HC}_{2} \mathrm{O}_{4}^{-},\) can be both a Bronsted acid and a Bronsted base.

Write balanced equations showing how the \(\mathrm{HPO}_{4}^{2-}\) ion of sodium hydrogen phosphate, \(\mathrm{Na}_{2} \mathrm{HPO}_{4},\) can be a Bronsted acid or a Bronsted base.

In each of the following acid-base reactions, identify the Bronsted acid and base on the left and their conjugate partners on the right. (a) \(\mathrm{HCO}_{2} \mathrm{H}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons\) \(\mathrm{HCO}_{2}^{-}(\mathrm{aq})+\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})\) (b) \(\mathrm{NH}_{3}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{S}(\mathrm{aq}) \rightleftarrows\) \(\mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{HS}^{-}(\mathrm{aq})\) (c) \(\mathrm{HSO}_{4}^{-}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \rightleftarrows\) \(\mathrm{SO}_{4}^{2-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\)

In each of the following acid-base reactions, identify the Bronsted acid and base on the left and their conjugate partners on the right. (a) \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}(\mathrm{aq})+\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\mathrm{aq}) \rightleftarrows\) \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+}(\mathrm{aq})+\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}(\mathrm{aq})\) (b) \(\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})+\mathrm{HSO}_{4}^{-}(\mathrm{aq}) \rightleftharpoons\) \(\mathrm{N}_{2} \mathrm{H}_{5}^{+}(\mathrm{aq})+\mathrm{SO}_{4}^{2-}(\mathrm{aq})\) (c) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \rightleftarrows\) \(\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{OH}\right]^{2+}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\)

An aqueous solution has a pH of \(3.75 .\) What is the hydronium ion concentration of the solution? Is it acidic or basic?

A saturated solution of milk of magnesia, \(\mathrm{Mg}(\mathrm{OH})_{2},\) has a pH of \(10.52 .\) What is the hydronium ion concentration of the solution? What is the hydroxide ion concentration? Is the solution acidic or basic?

What is the pH of a 0.0075 M solution of HCl? What is the hydroxide ion concentration of the solution?

What is the pH of a \(1.2 \times 10^{-4} \mathrm{M}\) solution of KOH? What is the hydronium ion concentration of the solution?

What is the pH of a 0.0015 M solution of \(\mathrm{Ba}(\mathrm{OH})_{2} ?\)

The \(\mathrm{pH}\) of a solution of \(\mathrm{Ba}(\mathrm{OH})_{2}\) is 10.66 at \(25^{\circ} \mathrm{C} .\) What is the hydroxide ion concentration in the solution? If the solution volume is \(125 \mathrm{mL}\) what mass of \(\mathrm{Ba}(\mathrm{OH})_{2}\) must have been dissolved?

The \(\mathrm{pH}\) of a solution of \(\mathrm{Ba}(\mathrm{OH})_{2}\) is 10.66 at \(25^{\circ} \mathrm{C} .\) What is the hydroxide ion concentration in the solution? If the solution volume is \(125 \mathrm{mL}\) what mass of \(\mathrm{Ba}(\mathrm{OH})_{2}\) must have been dissolved?

Write an equilibrium constant expression for the reaction of fluoride ion, a weak base, with water.

Several acids are listed here with their respective equilibrium constants: $$\begin{array}{l} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}^{-}(\mathrm{aq}) \\ \mathrm{K}_{\mathrm{a}}=1.3 \times 10^{-10} \\ \mathrm{HCO}_{2} \mathrm{H}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{HCO}_{2}^{-}(\mathrm{aq}) \\ K_{\mathrm{a}}=1.8 \times 10^{-4} \\ \mathrm{HC}_{2} \mathrm{O}_{4}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{C}_{2} \mathrm{O}_{4}^{2-}(\mathrm{aq}) \\\ K_{\mathrm{a}}=6.4 \times 10^{-5} \end{array}$$ (a) Which is the strongest acid? Which is the weakest acid? (b) Which acid has the weakest conjugate base? (c) Which acid has the strongest conjugate base?

Several acids are listed here with their respective equilibrium constants. $$\begin{aligned} &\mathrm{HF}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftarrows \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{F}^{-}(\mathrm{aq})\\\ &K_{\mathrm{a}}=7.2 \times 10^{-4}\\\ &\mathrm{HPO}_{4}^{2-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{PO}_{4}^{3-}(\mathrm{aq})\\\ &K_{\mathrm{a}}=3.6 \times 10^{-13}\\\ &\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}(\mathrm{aq})\\\ &K_{\mathrm{a}}=1.8 \times 10^{-5} \end{aligned}$$ (a) Which is the strongest acid? Which is the weakest acid? (b) What is the conjugate base of the acid HF? (c) Which acid has the weakest conjugate base? (d) Which acid has the strongest conjugate base?

Which of the following compounds or ions has the weakest conjugate base? Briefly explain your choice (a) HCN (b) HClO (c) \(\mathrm{NH}_{4}^{+}\)

Which of the following compounds or ions has the weakest conjugate acid? Briefly explain your choice. (a) \(\mathrm{HCO}_{3}^{-}\) (b) \(\mathrm{F}^{-}\) (c) \(\mathrm{NO}_{2}^{-}\)

Which of the following compounds or ions has the strongest conjugate acid? Briefly explain your choice. (a) CN (b) \(\mathrm{NH}_{3}\) (c) \(\mathrm{SO}_{4}^{2-}\)

Dissolving \(\mathrm{K}_{2} \mathrm{CO}_{3}\) in water gives a basic solution. Write a balanced equation showing how this can occur.

Dissolving \(\mathrm{K}_{2} \mathrm{CO}_{3}\) in water gives a basic solution. Write a balanced equation showing how this can occur.

If each of the salts listed here were dissolved in water to give a 0.10 M solution, which solution would have the highest \(\mathrm{pH}\) ? Which would have the lowest pH? (a) \(\mathrm{Na}_{2} \mathrm{S}\) (b) \(\mathrm{Na}_{3} \mathrm{PO}_{4}\) (c) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\) (d) NaF (e) \(\mathrm{NaCH}_{3} \mathrm{CO}_{2}\) (f) \(\mathrm{AlCl}_{3}\)

Which of the following common food additives would give a basic solution when dissolved in water? (a) \(\mathrm{NaNO}_{3}\) (used as a meat preservative) (b) \(\mathrm{NaC}_{6} \mathrm{H}_{5} \mathrm{CO}_{2}\) (sodium benzoate; used as a softdrink preservative) (c) \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) (used as an emulsifier in the manufacture of pasteurized cheese)

A weak acid has a \(K_{\mathrm{a}}\) of \(6.5 \times 10^{-5} .\) What is the value of \(\mathrm{p} K_{\mathrm{a}}\) for the acid?

If \(K_{\mathrm{a}}\) for a weak acid is \(2.4 \times 10^{-11},\) what is the value of \(\mathrm{p} K_{\mathrm{a}} ?\)

Which is the stronger of the following two acids? (a) benzoic acid, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO}_{2} \mathrm{H}, \mathrm{p} K_{\mathrm{a}}=4.20\) (b) 2 -chlorobenzoic acid, \(\mathrm{ClC}_{6} \mathrm{H}_{4} \mathrm{CO}_{2} \mathrm{H}, \mathrm{p} K_{3}=2.90\)

Which is the stronger of the following two acids? (a) acetic acid, \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}, K_{\mathrm{a}}=1.8 \times 10^{-5}\) (b) chloroacetic acid, \(\mathrm{ClCH}_{2} \mathrm{CO}_{2} \mathrm{H}, \mathrm{p} K_{a}=2.85\)

Chloroacetic acid \(\left(\mathrm{Cl} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\right)\) has \(K_{\mathrm{a}}=1.41 \times\) \(10^{-3} .\) What is the value of \(K_{\mathrm{b}}\) for the chloroacetate \(\operatorname{ion}\left(\mathrm{Cl} \mathrm{CH}_{2} \mathrm{CO}_{2}^{-}\right) ?\)

A weak base has \(K_{\mathrm{b}}=1.5 \times 10^{-9} .\) What is the value of \(K_{\mathrm{a}}\) for the conjugate acid?

The trimethylammonium ion, \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{NH}^{+}\), is the conjugate acid of the weak base trimethylamine, \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{N} .\) A chemical handbook gives 9.80 as the \(\mathrm{p} K_{\mathrm{a}}\) value for \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{NH}^{+} .\) What is the value of \(K_{\mathrm{b}}\) for \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{N} ?\)

The chromium(III) ion in water, \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+},\) is a weak acid with \(\mathrm{p} K_{\mathrm{a}}=3.95 .\) What is the value of \(K_{\mathrm{b}}\) for its conjugate base, \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{OH}\right]^{2+} ?\)

Equal molar quantities of hydrochloric acid and sodium hypochlorite (NaClO) are mixed. (a) Write the balanced, net ionic equation for the acid-base reaction that can, in principle, occur. (b) Does the equilibrium lie to the right or left?

Equal molar quantities of acetic acid and sodium hydrogen phosphate \(\left(\mathrm{Na}_{2} \mathrm{HPO}_{4}\right)\) are mixed. (a) Write a balanced, net ionic equation for the acid-base reaction that can, in principle, occur. (b) Does the equilibrium lie to the right or left?

Equal molar quantities of ammonia and sodium dihydrogen phosphate \(\left(\mathrm{NaH}_{2} \mathrm{PO}_{4}\right)\) are mixed. (a) Write a balanced, net ionic equation for the acid-base reaction that can, in principle, occur. (b) Does the equilibrium lie to the right or left?

A \(0.015 \mathrm{M}\) solution of hydrogen cyanate, HOCN, has a pH of 2.67 (a) What is the hydronium ion concentration in the solution? (b) What is the ionization constant, \(K_{a \prime}\) for the acid?

A \(0.10 \mathrm{M}\) solution of chloroacetic acid, \(\mathrm{Cl} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H},\) has a pH of \(1.95 .\) Calculate \(K_{\mathrm{a}}\) for the acid.

A \(0.025 \mathrm{M}\) solution of hydroxylamine has a pH of 9.11. What is the value of \(K_{\mathrm{b}}\) for this weak base? $$\mathrm{H}_{2} \mathrm{NOH}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{NOH}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})$$

Methylamine, \(\mathrm{CH}_{3} \mathrm{NH}_{2},\) is a weak base. \(\mathrm{CH}_{3} \mathrm{NH}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{CH}_{3} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})\) If the \(p H\) of a \(0.065 \mathrm{M}\) solution of the amine is \(11.70,\) what is the value of \(K_{\mathrm{b}} ?\)

A \(2.5 \times 10^{-3} \mathrm{M}\) solution of an unknown acid has a pH of 3.80 at \(25^{\circ} \mathrm{C}\) (a) What is the hydronium ion concentration of the solution? (b) Is the acid a strong acid, a moderately weak acid \(\left(K_{\mathrm{a}} \text { of about } 10^{-5}\right)\) Or a very weak acid\(\left(K_{\mathrm{a}} \text { of about } 10^{-10}\right) ?\)

A \(0.015 \mathrm{M}\) solution of a base has a pH of 10.09 (a) What are the hydronium and hydroxide ion concentrations of this solution? (b) Is the base a strong base, a moderately weak base \(\left(K_{\mathrm{b}} \text { of about } 10^{-5}\right)\) Or a very weak base \(\left(K_{\mathrm{b}} \text { of about } 10^{-10}\right) ?\)

The ionization constant of a very weak acid, HA, is \(4.0 \times 10^{-9} .\) Calculate the equilibrium concentrations of \(\mathrm{H}_{3} \mathrm{O}^{+}, \mathrm{A}^{-},\) and \(\mathrm{HA}\) in a \(0.040 \mathrm{M}\) solution of the acid.

A hypothetical weak base has \(K_{\mathrm{b}}=5.0 \times 10^{-4}\) Calculate the equilibrium concentrations of the base, its conjugate acid, and \(\mathrm{OH}^{-}\) in a \(0.15 \mathrm{M}\) solution of the base.

The weak base methylamine, \(\mathrm{CH}_{3} \mathrm{NH}_{2},\) has \(K_{\mathrm{b}}=\) \(4.2 \times 10^{-4} .\) It reacts with water according to the equation \(\mathrm{CH}_{3} \mathrm{NH}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{CH}_{3} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})\) Calculate the equilibrium hydroxide ion concentration in a \(0.25 \mathrm{M}\) solution of the base. What are the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of the solution?

Calculate the \(\mathrm{pH}\) of a \(0.12 \mathrm{M}\) aqueous solution of the base aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\left(K_{\mathrm{b}}=4.0 \times 10^{-10}\right)\) $$\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftarrows {\mathrm{C}_{6}} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})$$

Sodium cyanide is the salt of the weak acid HCN. Calculate the concentrations of \(\mathrm{H}_{3} \mathrm{O}^{+}, \mathrm{OH}^{-}\) HCN, and \(\mathrm{Na}^{+}\) in a solution prepared by dissolving 10.8 g of NaCN in enough water to make \(5.00 \times 10^{2} \mathrm{mL}\) of solution at \(25^{\circ} \mathrm{C}\).

Calculate the hydronium ion concentration and pH of the solution that results when \(22.0 \mathrm{mL}\) of \(0.15 \mathrm{M}\) acetic acid, \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H},\) is mixed with \(22.0 \mathrm{mL}\) of \(0.15 \mathrm{M} \mathrm{NaOH}\).

Calculate the hydronium ion concentration and the pH when 50.0 mL of \(0.40 \mathrm{M} \mathrm{NH}_{3}\) is mixed with \(50.0 \mathrm{mL}\) of \(0.40 \mathrm{M} \mathrm{HCl}\).

For each of the following cases, decide whether the \(\mathrm{pH}\) is less than \(7,\) equal to \(7,\) or greater than 7 (a) Equal volumes of 0.10 M acetic acid, \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H},\) and \(0.10 \mathrm{M} \mathrm{KOH}\) are mixed. (b) \(25 \mathrm{mL}\) of \(0.015 \mathrm{M} \mathrm{NH}_{3}\) is mixed with \(25 \mathrm{mL}\) of 0.015 M HCl. (c) \(150 \mathrm{mL}\) of \(0.20 \mathrm{M} \mathrm{HNO}_{3}\) is mixed with \(75 \mathrm{mL}\) of 0.40 M NaOH.