Chapter 14

Amantadine, \(\mathrm{C}_{10} \mathrm{H}_{15} \mathrm{NH}_{2}\), is a weak base used in the treatment of Parkinson's disease. Its conjugate acid has \(K_{\mathrm{a}}=\) \(7.9 \times 10^{-11}\). Calculate the pH of a 0.0010-M aqueous solution of amantadine at \(25^{\circ} \mathrm{C}\).

Pyridine, \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N},\) is a weak base; its conjugate acid has \(K_{\mathrm{a}}=6.3 \times 10^{-6} . \mathrm{A} 0.2-\mathrm{M}\) solution of pyridine has \(\mathrm{pH}=8.5 .\) Calculate the concentration of unreacted pyridine in this solution.

Lactic acid, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}\), occurs in sour milk as a result of the metabolism of certain bacteria. Calculate the pH of a solution of 56. mg lactic acid in 250. mL water. \(K_{\mathrm{a}}\) for D-lactic acid is \(1.5 \times 10^{-4}\).

Boric acid is a weak acid often used as an eyewash. \(K_{\mathrm{a}}\) for boric acid is \(5.8 \times 10^{-10} .\) Calculate the \(\mathrm{pH}\) of a 0.10-M solution of boric acid.

Complete each of these reactions by filling in the blanks. Predict whether each reaction is product-favored or reactant-favored, and explain your reasoning. (a) _________ \((\mathrm{aq})+\mathrm{HSO}_{4}^{-}(\mathrm{aq}) \rightleftharpoons \mathrm{HCN}(\mathrm{aq})+\mathrm{SO}_{4}^{2-}(\mathrm{aq})\) (b) \(\mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+\) ____________ (aq) (c) \(\mathrm{H}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{OH}^{-}(\mathrm{aq})+\) ______________ (g)

For each salt, predict whether an aqueous solution has a pH less than, equal to, or greater than 7 . Explain your prediction. (a) \(\mathrm{AlCl}_{3}\) (b) \(\mathrm{Na}_{2} \mathrm{~S}\) (c) \(\mathrm{NaNO}_{3}\)

For each salt, predict whether an aqueous solution has a pH less than, equal to, or greater than 7 . Explain your prediction. (a) \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) (b) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{~S}\) (c) \(\mathrm{KCH}_{3} \mathrm{COO}\)

Explain why \(\mathrm{BaCO}_{3}\) is soluble in aqueous \(\mathrm{HCl}\), but \(\mathrm{BaSO}_{4}\), which is used to make the intestines visible in X-ray photographs, remains sufficiently insoluble in the \(\mathrm{HCl}\) in a human stomach so that poisonous barium ions do not get into the bloodstream.

Which of these substances has greater solubility at \(\mathrm{pH}=2\) than at \(\mathrm{pH}=7 ?\) (a) \(\mathrm{Cu}(\mathrm{OH})_{2}\) (b) \(\mathrm{CuSO}_{4}\) (c) \(\mathrm{CuCO}_{3}\) (d) \(\mathrm{CuS}\) (e) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)

Write a chemical equation that illustrates how the hydrated \(\mathrm{Ni}^{2+}\) ion, \(\left[\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\), acts as an acid in aqueous solution.

Which of these is a Lewis acid? A Lewis base? (a) \(\mathrm{O}^{2-}\) (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{H}^{-}\)

Which of these is a Lewis acid? A Lewis base? (a) \(\mathrm{Al}^{3+}\) (b) \(\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{SCN}^{-}\)

Which of these is a Lewis acid? A Lewis base? (a) \(\mathrm{Cr}^{3+}\) (b) \(\mathrm{SO}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\)

Which of these is a Lewis acid? A Lewis base? (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{BeCl}_{2}\) (c) \(\mathrm{BCl}_{3}\)

Identify the Lewis acid and the Lewis base in each reaction. (a) \(\mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{SO}_{2}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2} \mathrm{SO}_{3}(\mathrm{aq})\) (b) \(\mathrm{H}_{3} \mathrm{BO}_{3}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \longrightarrow \mathrm{B}(\mathrm{OH})_{4}^{-}(\mathrm{aq})\) (c) \(\mathrm{Cu}^{2+}(\mathrm{aq})+4 \mathrm{NH}_{3}(\mathrm{aq}) \longrightarrow\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}(\mathrm{aq})\) (d) \(2 \mathrm{Cl}^{-}(\mathrm{aq})+\mathrm{SnCl}_{2}(\mathrm{aq}) \longrightarrow \mathrm{SnCl}_{4}^{2-}(\mathrm{aq})\)

Identify the Lewis acid and the Lewis base in each reaction. (a) \(\mathrm{I}_{2}(\mathrm{~s})+\mathrm{I}^{-}(\mathrm{aq}) \longrightarrow \mathrm{I}_{3}^{-}(\mathrm{aq})\) (b) \(\mathrm{SO}_{2}(\mathrm{~g})+\mathrm{BF}_{3}(\mathrm{~g}) \longrightarrow \mathrm{O}_{2} \mathrm{SBF}_{3}(\mathrm{~s})\) (c) \(\mathrm{Au}^{+}(\mathrm{aq})+2 \mathrm{CN}^{-}(\mathrm{aq}) \longrightarrow\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-}(\mathrm{aq})\) (d) \(\mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{H}_{2} \mathrm{CO}_{3}(\mathrm{aq})\)

Trimethylamine, \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}:\), reacts readily with diborane, \(\mathrm{B}_{2} \mathrm{H}_{6}\). The diborane dissociates to two \(\mathrm{BH}_{3}\) fragments, each of which can react with trimethylamine to form a complex, \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}: \mathrm{B} \mathrm{H}_{3}\). Write an equation for this reaction and interpret it in terms of Lewis acid-base theory.

Draw a Lewis structure for \(\mathrm{ICl}_{3} .\) Predict the shape of this molecule. Does it function as a Lewis acid or base when it reacts with chloride ion to form \(\mathrm{ICl}_{4}^{-}\) ? What is the structure of this ion?

Write the formula for the conjugate acid of \(\left[\mathrm{Zn}(\mathrm{OH})_{4}\right]^{2-} .\)

Write the formula for the conjugate base of \(\left[\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3}(\mathrm{OH})\right]^{1+}\).

Double-acting baking powder contains two salts, sodium hydrogen carbonate and potassium dihydrogen phosphate, whose anions react in water to form \(\mathrm{CO}_{2}\) gas. Write a balanced chemical equation for the reaction. Which anion is the acid and which is the base?

Common soap is made by reacting sodium carbonate with stearic acid, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH}\). Write a balanced equation for the reaction.

Why is it not a good idea to substitute dishwashing detergent for automobile- washing detergent?

Why do cleaning products containing sodium hydroxide feel slippery when you get them on your skin?

Some cooked fish have a "fishy" odor due to amines. Explain why putting lemon juice on the fish reduces this odor.

Classify each of these as a strong acid, weak acid, strong base, weak base, amphiprotic substance, or neither acid nor base. (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) (b) \(\mathrm{Na}_{2} \mathrm{O}\) (c) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{NH}_{3}\) (e) \(\mathrm{Ba}(\mathrm{OH})_{2}\) (f) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

Classify each of these as a strong acid, weak acid, strong base, weak base, amphiprotic substance, or neither acid nor base. (a) \(\mathrm{HCl}\) (b) \(\mathrm{NH}_{4}^{+}\) (c) \(\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) (e) \(\mathrm{CH}_{4}\) (f) \(\mathrm{CO}_{3}^{2-}\)

Several acids and their respective equilibrium constants are: $$ \begin{array}{ll} \mathrm{HF} & K_{\mathrm{a}}=6.8 \times 10^{-4} \\ \mathrm{HS}^{-} & K_{\mathrm{a}}=1 \times 10^{-19} \\ \mathrm{CH}_{3} \mathrm{COOH} & K_{\mathrm{a}}=1.8 \times 10^{-5} \end{array} $$ (a) Which is the strongest acid? (b) Which is the weakest acid? (c) Which acid has the weakest conjugate base? (d) Which acid has the strongest conjugate base?

State whether equal molar amounts of these would have a \(\mathrm{pH}\) equal to 7 , less than 7 , or greater than 7 . (a) A weak base and a strong acid react. (b) A strong base and a strong acid react. (c) A strong base and a weak acid react.

Ascorbic acid (vitamin \(\left.\mathrm{C}, \mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}\right)\) is a diprotic acid \(\left(K_{\mathrm{a}_{1}}=7.9 \times 10^{-5}, K_{\mathrm{a}_{2}}=1.6 \times 10^{-12}\right) .\) Calculate the \(\mathrm{pH}\) of a solution that contains \(5.0 \mathrm{mg}\) acid per mL water. (Assume that only the first ionization is important in determining pH.)

Does the \(\mathrm{pH}\) of the solution increase, decrease, or stay the same when you (a) Add solid ammonium chloride to \(100 . \mathrm{mL}\) of \(0.10-\mathrm{M} \mathrm{NH}_{3} ?\) (b) Add solid sodium acetate to \(50.0 \mathrm{~mL}\) of \(0.015-\mathrm{M}\) acetic acid? (c) Add solid \(\mathrm{NaCl}\) to \(25.0 \mathrm{~mL}\) of \(0.10-\mathrm{M} \mathrm{NaOH}\) ?

Does the \(\mathrm{pH}\) of the solution increase, decrease, or stay the same when you (a) Add solid sodium oxalate, \(\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4},\) to \(50.0 \mathrm{~mL}\) of 0.015-M oxalic acid? (b) Add solid ammonium chloride to \(100 . \mathrm{mL}\) of \(0.016-\mathrm{M} \mathrm{HCl} ?\) (c) Add \(20.0 \mathrm{~g} \mathrm{NaCl}\) to \(1.0 \mathrm{~L}\) of \(0.012-\mathrm{M}\) sodium acetate, \(\mathrm{NaCH}_{3} \mathrm{COO} ?\)

Sodium hypochlorite, \(\mathrm{NaOCl}\), is used as a source of chlorine in some laundry bleaches, swimming pool disinfectants, and water treatment plants. Calculate the pH of a 0.010-M solution of \(\mathrm{NaOCl}\left(K_{\mathrm{b}}=1.5 \times 10^{-7}\right)\).

Some commercial baking powders contain a dry mixture of aluminum sulfate and sodium hydrogen carbonate. When it is mixed with water and baking dough, a reaction occurs that produces a gas that makes the dough rise. Identify the gas and write balanced chemical equations for the reactions that create it. Explain the role of water in the process.

From the mid-1800s to the present, the average acidity of the oceans' surface water has increased \(30 \%\) to its current \(\mathrm{pH}\) of \(8.1 .\) Calculate what the \(\mathrm{pH}\) was in the mid-1800s.

Carbon dioxide released from burning of fossil fuels contributes to the acidity of the oceans' surface water, whose current average \(\mathrm{pH}\) is \(8.1 .\) It has been estimated that if \(\mathrm{CO}_{2}\) emissions are not curbed, the oceans' surface water pH could drop to 7.8 by the end of this century. Calculate the percent change in acidity if that were to happen.

Ammonium lactate, a salt, is used as a moisturizing agent in medicinal creams. (a) Identify the acid and the base that form ammonium lactate by a neutralization reaction. (b) Predict whether an ammonium lactate solution is acidic, neutral, or basic. Explain your answer. (c) A medicinal cream contains \(12 \%\) ammonium lactate by weight. Calculate the amount (mol) of ammonium lactate in \(1.5 \mathrm{~g}\) of this cream. (d) Calculate the total number of ammonium and lactate ions in the \(1.5 \mathrm{~g}\) sample.

When a 0.1-M aqueous ammonia solution is tested with a conductivity apparatus ( \(\in\) Sec. \(3-3 b\) ), the bulb glows dimly. When a 0.1-M hydrochloric acid solution is tested, the bulb glows brightly. As water is added to each of the solutions, predict whether the bulb glows brighter, stops glowing, or stays the same. Explain your reasoning.

When all the water is evaporated from a sodium hydroxide solution, solid sodium hydroxide is obtained. However, if you evaporate the water in an ammonium hydroxide solution, you will not produce solid ammonium hydroxide. Explain why. What will remain after the water is evaporated?