第15章その他の反応の平衡

Even though Ca(OH)₂ is an inexpensive base, its limited solubility restricts its use. What is the pH of a saturated solution of Ca(OH)₂?

Under what circumstances, if any, does a sample of solid AgCl completely dissolve in pure water?

Explain why the addition of NH₃ or HNO₃ to a saturated solution of Ag₂CO₃ in contact with solid Ag₂CO₃ increases the solubility of the solid.

Calculate the cadmium ion concentration, [Cd²⁺], in a solution prepared by mixing 0.100 L of 0.0100 M Cd(NO₃)₂ with 0.150 L of 0.100 NH₃(aq).

Explain why addition of NH₃ or HNO₃ to a saturated solution of Cu(OH)₂ in contact with solid Cu(OH)₂ increases the solubility of the solid.

Sometimes equilibria for complex ions are described in terms of dissociation constants, K_d. For the complex ion ${\text{AlF}}_6{}^{\text{3−}}$ the dissociation reaction is:

${\text{AlF}}_6{}^{\text{3−}}\rightleftharpoons {\text{Al}}^{\text{3+}}+6{\text{F}}^{\text{−}}$ and $K_{\text{d}}=\frac{[{\text{Al}}^{\text{3+}}]{[{\text{F}}^{\text{−}}]}^6}{[{\text{AlF}}_6{}^{\text{3−}}]}=2\times {10}^{-24}$

Calculate the value of the formation constant, K_f, for ${\text{AlF}}_{\text{6}}{}^{\text{3−}}.$

Using the value of the formation constant for the complex ion $\text{Co}{({\text{NH}}_3)}_6{}^{\text{2+}},$ calculate the dissociation constant.

Using the dissociation constant, K_d = 3.3 $\times$ 10^–19, calculate the equilibrium concentrations of Cd²⁺ and CN^– in a 0.250-M solution of $\text{Cd}{(\text{CN})}_4{}^{\text{2−}}.$

Using the dissociation constant, K_d = 3.4 $\times$ 10^–15, calculate the equilibrium concentrations of Zn²⁺ and OH^– in a 0.0465-M solution of $\text{Zn}{(\text{OH})}_4{}^{\text{2−}}.$

Using the dissociation constant, K_d = 2.2 $\times$ 10^–34, calculate the equilibrium concentrations of Co³⁺ and NH₃ in a 0.500-M solution of $\text{Co}{({\text{NH}}_3)}_6{}^{\text{3+}}.$

Using the dissociation constant, K_d = 1 $\times$ 10^–44, calculate the equilibrium concentrations of Fe³⁺ and CN^– in a 0.333 M solution of $\text{Fe}{(\text{CN})}_6{}^{\text{3−}}.$

Calculate the mass of potassium cyanide ion that must be added to 100 mL of solution to dissolve 2.0 $\times$ 10^–2 mol of silver cyanide, AgCN.

Calculate the minimum concentration of ammonia needed in 1.0 L of solution to dissolve 3.0 $\times$ 10^–3 mol of silver bromide.

A roll of 35-mm black and white photographic film contains about 0.27 g of unexposed AgBr before developing. What mass of Na₂S₂O₃·5H₂O (sodium thiosulfate pentahydrate or hypo) in 1.0 L of fixer is required to dissolve the AgBr as $\text{Ag}{({\text{S}}_2{\text{O}}_3)}_2{}^{\text{3−}}$ (K_f = 4.7 $\times$ 10¹³)?

We have seen an introductory definition of an acid: An acid is a compound that reacts with water and increases the amount of hydronium ion present. In the chapter on acids and bases, we saw two more definitions of acids: a compound that donates a proton (a hydrogen ion, H⁺) to another compound is called a Brønsted-Lowry acid, and a Lewis acid is any species that can accept a pair of electrons. Explain why the introductory definition is a macroscopic definition, while the Brønsted-Lowry definition and the Lewis definition are microscopic definitions.

Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:

(a) ${\text{CO}}_2+{\text{OH}}^{\text{−}}⟶{\text{HCO}}_3{}^{\text{−}}$

(b) $\text{B}{(\text{OH})}_3+{\text{OH}}^{\text{−}}⟶\text{B}{(\text{OH})}_4{}^{\text{−}}$

(c) ${\text{I}}^{\text{−}}+{\text{I}}_2⟶{\text{I}}_3{}^{\text{−}}$

(d) ${\text{AlCl}}_3+{\text{Cl}}^{\text{−}}⟶{\text{AlCl}}_4{}^{\text{−}}$ (use Al-Cl single bonds)

(e) ${\text{O}}^{\text{2−}}+{\text{SO}}_3⟶{\text{SO}}_4{}^{\text{2−}}$

Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:

(a) ${\text{CS}}_2+{\text{SH}}^{\text{−}}⟶{\text{HCS}}_3{}^{\text{−}}$

(b) ${\text{BF}}_3+{\text{F}}^{\text{−}}⟶{\text{BF}}_4{}^{\text{−}}$

(c) ${\text{I}}^{\text{−}}+{\text{SnI}}_2⟶{\text{SnI}}_3{}^{\text{−}}$

(d) $\text{Al}{(\text{OH})}_3+{\text{OH}}^{\text{−}}⟶\text{Al}{(\text{OH})}_4{}^{\text{−}}$

(e) ${\text{F}}^{\text{−}}+{\text{SO}}_3⟶{\text{SFO}}_3{}^{\text{−}}$

Using Lewis structures, write balanced equations for the following reactions:

(a) $\text{HCl}(g)+{\text{PH}}_3(g)⟶$

(b) ${\text{H}}_3{\text{O}}^{\mathrm{+}}+{\text{CH}}_3{}^{\text{−}}⟶$

(c) $\text{CaO}+{\text{SO}}_3⟶$

(d) ${\text{NH}}_4{}^{\mathrm{+}}+{\text{C}}_2{\text{H}}_5{\text{O}}^{\text{−}}⟶$

Calculate $[{\text{HgCl}}_4{}^{\text{2−}}]$ in a solution prepared by adding 0.0200 mol of NaCl to 0.250 L of a 0.100-M HgCl₂ solution.

In a titration of cyanide ion, 28.72 mL of 0.0100 M AgNO₃ is added before precipitation begins. [The reaction of Ag⁺ with CN^– goes to completion, producing the $\text{Ag}{(\text{CN})}_2{}^{\text{−}}$ complex.] Precipitation of solid AgCN takes place when excess Ag⁺ is added to the solution, above the amount needed to complete the formation of $\text{Ag}{(\text{CN})}_2{}^{\text{−}}.$ How many grams of NaCN were in the original sample?

What are the concentrations of Ag⁺, CN^–, and $\text{Ag}{(\text{CN})}_2{}^{\text{−}}$ in a saturated solution of AgCN?

In dilute aqueous solution HF acts as a weak acid. However, pure liquid HF (boiling point = 19.5 °C) is a strong acid. In liquid HF, HNO₃ acts like a base and accepts protons. The acidity of liquid HF can be increased by adding one of several inorganic fluorides that are Lewis acids and accept F^– ion (for example, BF₃ or SbF₅). Write balanced chemical equations for the reaction of pure HNO₃ with pure HF and of pure HF with BF₃.

The simplest amino acid is glycine, H₂NCH₂CO₂H. The common feature of amino acids is that they contain the functional groups: an amine group, –NH₂, and a carboxylic acid group, –CO₂H. An amino acid can function as either an acid or a base. For glycine, the acid strength of the carboxyl group is about the same as that of acetic acid, CH₃CO₂H, and the base strength of the amino group is slightly greater than that of ammonia, NH₃.

(a) Write the Lewis structures of the ions that form when glycine is dissolved in 1 M HCl and in 1 M KOH.

(b) Write the Lewis structure of glycine when this amino acid is dissolved in water. (Hint: Consider the relative base strengths of the –NH₂ and $-{\text{CO}}_2{}^{\text{−}}$ groups.)

Boric acid, H₃BO₃, is not a Brønsted-Lowry acid but a Lewis acid. (Hint: See the equation in Exercise 76)

(a) Write an equation for its reaction with water.

(b) Predict the shape of the anion thus formed.

(c) What is the hybridization on the boron, and is it consistent with the shape you have predicted?