Chapter 17

Explain why a common ion lowers the solubility of an ionic compound.

Describe the solution that results when two solutions are mixed and \(Q_{s p}\) is found to equal \(K_{\mathrm{sp}} .\) Does a precipitate form?

Write the \(K_{s p}\) expression for lead chromate \(\left(\mathrm{Pb} \mathrm{CrO}_{4}\right)\) and calculate its solubility in mol/L. \(K_{\mathrm{sp}}=2.3 \times 10^{-13}\)

At \(350^{\circ} \mathrm{C}, K_{\mathrm{eq}}=1.67 \times 10^{-2}\) for the reversible reaction \(2 \mathrm{HI}(\mathrm{g}) \rightleftharpoons \mathrm{H}^{2}(\mathrm{g})+\mathrm{I}^{2}(\mathrm{g}) .\) What is the concentration of HI at equilibrium if \(\left[\mathrm{H}^{2}\right]\) is \(2.44 \times 10^{-3} \mathrm{M}\) and \(\left[\mathrm{I}^{2}\right]\) is \(7.18 \times 10^{-5} \mathrm{M} ?\)

\(K_{\mathrm{sp}}\) for scandium fluoride \(\left(\mathrm{ScF}_{3}\right)\) at 298 \(\mathrm{K}\) is \(4.2 \times 10^{-18}\) Write the chemical equation for the solubility equilibrium of scandium fluoride in water. What concentration of \(\mathrm{Sc}^{3+}\) ions is required to cause a precipitate to form if the fluoride-ion concentration is 0.076 \(\mathrm{M}\) ?

Manufacturing Ethyl acetate \(\left(\mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{CH}_{3}\right), \mathrm{a}\) solvent used in making varnishes and lacquers, can be produced by the reaction between ethanol and acetic acid. The equilibrium system is described by the equation \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \rightleftharpoons\) $$ \mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{CH}_{3}+\mathrm{H}_{2} \mathrm{O} $$ Calculate \(K_{\text { eq using these equilibrium concentrations: }}\) \(\left[\mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{CH}_{3}\right]=2.90 M,\left[\mathrm{CH}_{3} \mathrm{COOH}\right]=0.316 M,\) \(\left[\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right]=0.313 M,\) and \(\left[\mathrm{H}_{2} \mathrm{O}\right]=0.114 M\)

Ethyl acetate \(\left(\mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{CH}_{3}\right)\) is produced in the equilibrium system described by the following equation. \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} \rightleftharpoons\) $$ \mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{CH}_{3}+\mathrm{H}_{2} \mathrm{O} $$ Why does the removal of water result in the production of more ethyl acetate?

How would these equilibria be affected by decreasing the temperature? $$ \begin{array}{l}{\text { a. } 2 \mathrm{O}_{3}(\mathrm{g}) \rightleftharpoons 3 \mathrm{O}_{2}(\mathrm{g})+\text { heat }} \\ {\text { b. heat }+\mathrm{H}_{2}(\mathrm{g})+\mathrm{F}_{2}(\mathrm{g}) \rightleftharpoons 2 \mathrm{HF}(\mathrm{g})}\end{array} $$

How would simultaneously increasing the temperature and volume of the system affect these equilibria? $$ \begin{array}{l}{\text { a. } 2 \mathrm{O}_{3}(\mathrm{g}) \rightleftharpoons 3 \mathrm{O}_{2}(\mathrm{g})+\text { heat }} \\ {\text { b. heat }+\mathrm{N}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightleftharpoons 2 \mathrm{NO}(\mathrm{g})}\end{array} $$

The solubility product constant for lead(II) arsenate \(\left(\mathrm{Pb}_{3}\left(\mathrm{AsO}_{4}\right)_{2}\right)\) is \(4.0 \times 10^{-36}\) at 298 \(\mathrm{K}\) . Calculate the molar solubility of the compound at this temperature.

Evaluate this statement: A low value for Keq means that both the forward and reverse reactions are occurring slowly.

Describe the process by which adding potassium hydroxide to a saturated aluminum hydroxide solution reduces the concentration of aluminum ions. Write the solubility equilibrium equation and solubility product constant expression for a saturated aqueous solution of aluminum hydroxide.

At \(298 \mathrm{K}, K_{\text { sp }}\) for cadmium iodate \(\left(\mathrm{Cd}\left(\mathrm{IO}_{3}\right)_{2}\right)\) equals \(2.3 \times 10^{-8} .\) What are the molar concentrations of cadmium ions and iodate ions in a saturated solution at 298 \(\mathrm{K} ?\)

Analyze Suppose that an equilibrium system at a given temperature has a \(K_{\text { eq equal to } 1.000 . \text { Evaluate the possi- }}\) bility that such a system is made up of 50\(\%\) reactants and 50\(\%\) products. Explain your answer.

Evaluate Imagine that you are a chemical engineer designing a production facility for a particular process. The process will utilize a reversible reaction that reaches a state of equilibrium. Analyze the merits of a continuous-flow process or a batch process for such a reaction and determine which is preferable. As a reaction proceeds in a continuous-flow process, reactants are continuously introduced into the reaction chamber and products are continuously removed from the chamber. In a batch process, the reaction chamber is charged with reactants, the reaction is allowed to occur, and the chamber is later emptied of all materials.

Interpret Data What compound would precipitate first if a 0.500M sodium fluoride solution were added gradually to a solution already containing 0.500M concentrations of both barium ions and magnesium ions? Use the data in Table 17.6. Write the solubility equilibrium equations and solubility product constant expressions for both compounds. Explain your answer.

Apply Smelling salts, sometimes used to revive a person who is unconscious, are made of ammonium carbonate. The equation for the endothermic decomposition of ammonium carbonate is as follows. $$ \left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}(\mathrm{s}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) $$ .Would you expect smelling salts to work as well on a cold winter day as on a warm summer day? Explain your answer.

Recognize Cause and Effect Suppose you have 12.56 \(\mathrm{g}\) of a mixture made up of sodium chloride and barium chloride. Explain how you could use a precipitation reaction to determine how much of each compound the mixture contains.

Compare and Contrast Which of the two solids, calcium phosphate or iron(III) phosphate, has the greater molar solubility? \(K_{s p}\left(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\right)=1.2 \times 10^{-29}\) \(K_{\mathrm{sp}}\left(\mathrm{FePO}_{4}\right)=1.0 \times 10^{-22} .\) Which compound has the greater solubility, expressed in grams per liter?

Synthesis of Phosgene Phosgene \(\left(\mathrm{COCl}_{2}\right)\) is a toxic gas that is used in the manufacture of certain dyes, pharma- ceuticals, and pesticides. Phosgene can be produced by the reaction between carbon monoxide and chlorine described by the equation \(\mathrm{CO}(\mathrm{g})+\mathrm{Cl}_{2}(\mathrm{g}) \rightleftharpoons \mathrm{COCl}_{2}(\mathrm{g})\) . Initially 1.0000 \(\mathrm{mol} \mathrm{CO}\) and 1.0000 \(\mathrm{mol} \mathrm{Cl}_{2}\) are intro- duced into a 10.00 -L reaction vessel. When equilibrium is established, both of their molar concentrations are found to be 0.0086 \(\mathrm{mol} / \mathrm{L}\) . What is the molar concentration of phosgene at equilibrium? What is \(K_{\mathrm{eq}}\) for the system?

Explain the general trend in ionization energy as you go from left to right along Periods \(1-5\) of the periodic table. (Chapter 6 )

How are the lengths of covalent bonds related to their strength? (Chapter 8\()\)

How are the chemical bonds in \(\mathrm{H}_{2}, \mathrm{O}_{2},\) and \(\mathrm{N}_{2}\) different? (Chapter 8\()\)

How can you tell if a chemical equation is balanced? (Chapter 9\()\)

What mass of carbon must burn to produce 4.56 \(\mathrm{L} \mathrm{CO}_{2}\) gas at STP? (Chapter 11) $$ \mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g}) $$

Describe a hydrogen bond. What conditions must exist for a hydrogen bond to form? (Chapter 12\()\)

When you reverse a thermochemical equation, why must you change the sign of \(\Delta H ?(\text { Chapter } 15)\)

What is the sign of the free energy change, \(\Delta G^{\circ}\) system for a spontaneous reaction? (Chapter 15\()\)

A New Compound Imagine that you are a scientist who has created a unique new liquid. You have named the liquid yollane, abbreviated yo. Yollane is nontoxic, inexpensive to make, and can dissolve huge volumes of gaseous carbon dioxide in the equilibrium \(\mathrm{CO}_{2}(\mathrm{g}) \rightleftharpoons \mathrm{CO}_{2}(\mathrm{yo}), \mathrm{Keq}=3.4 \times 10^{6}\) . Write a news- paper or magazine article that explains the merits of yollane in combating global warming.

Hard Water The presence of magnesium and calcium ions in water makes the water “hard.” Explain in terms of solubility why the presence of these ions is often undesirable. Find out what measures can be taken to eliminate them.

Examine the relationship between \(K\) eq and temperature. Use Le Châtelier's principle to deduce whether the forward reaction is exothermic or endothermic.

Explain how automobile radiators plated with the alloy might help reduce the atmospheric concentrations of NO and \(\mathrm{CO}\) .