Chapter 16

Draw Lewis structures that show how electron pairs move and bonds form and break in the following reaction, and identify the Lewis acid and Lewis base. $$ \mathrm{SeO}_{3}(g)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{H}_{2} \mathrm{SeO}_{4}(a q) $$

Draw Lewis structures that show how electron pairs move and bonds form and break in the following reaction, and identify the Lewis acid and Lewis base. $$\mathrm{B}(\mathrm{OH})_{3}(a q)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightleftharpoons \mathrm{B}(\mathrm{OH})_{4}^{-}(a q)+\mathrm{H}_{3} \mathrm{O}^{+}(a q)$$

Draw Lewis structures that show how electron pairs move and bonds form and break in the following reaction, and identify the Lewis acid and Lewis base. $$ \mathrm{SbF}_{5}(s)+\mathrm{HF}(g) \rightarrow \mathrm{HSbF}_{6}(s) $$

When \(\mathrm{CaCl}_{2}\) dissolves in water, which molecules or ions occupy the inner coordination sphere around the \(\mathrm{Ca}^{2+}\) ions?

When AgNO, dissolves in water, which molecules or ions occupy the inner coordination sphere around the \(\mathrm{Ag}^{+}\) ions?

A lab technician cleaning glassware that contains residues of AgCl washes the glassware with an aqueous solution of ammonia. The \(\mathrm{AgCl}\), which is insoluble in water, rapidly dissolves in the ammonia solution. Why?

Which, if any, aqueous solutions of the following chloride compounds are acidic? (a) \(\mathrm{CaCl}_{2} ;\) (b) \(\mathrm{CrCl}_{3} ;\) (c) \(\mathrm{NaCl}\) (d) \(\mathrm{FeCl}_{3}\)

If \(0.100 M\) aqueous solutions of each of these compounds were prepared, which one would have the lowest pH? (a) \(\mathrm{BaCl}_{2} ;\) (b) \(\mathrm{LiCl} ;\) (c) \(\mathrm{KCl} ;\) (d) \(\mathrm{TiCl}_{4}\)

When ozone is bubbled through an aqueous solution of \(\mathrm{Fe}^{2+}\) ions, the ions are oxidized to \(\mathrm{Fe}^{3+}\) ions. How does the oxidation process affect the pH of the solution?

As an aqueous solution of KOH is slowly added to a stirred solution of \(\mathrm{AlCl}_{3},\) the mixture becomes cloudy but then clears when more KOH is added. a. Explain the chemical changes responsible for the changes in the appearance of the mixture. b. Would you expect to observe the same changes if \(\mathrm{KOH}\) were added to a solution of \(\mathrm{FeCl}_{3} ?\) Explain why or why not.

Chromium(III) hydroxide is amphiprotic. Write chemical equations showing how an aqueous suspension of this compound reacts to the addition of a strong acid and the addition of a strong base.

Zinc hydroxide is amphiprotic. Write chemical equations showing how an aqueous suspension of this compound reacts to the addition of a strong acid and the addition of a strong base.

To remove impurities such as calcium and magnesium carbonates and \(\mathrm{Fe}(\mathrm{III})\) oxides from aluminum ore (which is mostly \(\mathrm{Al}_{2} \mathrm{O}_{3}\) ), the ore is treated with a strongly basic solution. In this treatment, \(\mathrm{Al}^{3+}\) dissolves but the other metal ions do not. Why?

Exactly \(1.00 \mathrm{g}\) of \(\mathrm{FeCl}_{3}\) is dissolved in each of four \(0.500 \mathrm{L}\) samples: \(1 M \mathrm{HNO}_{3}, 1 \mathrm{MHNO}_{2}, 1 \mathrm{MCH}_{3} \mathrm{COOH},\) and pure water. Is the concentration of \(\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{3+}\) ions the same in all four solutions? Explain why or why not.

What is the pH of \(0.25 M \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3} ?\)

What is the pH of \(0.50 M \mathrm{CrCl}_{3} ?\)

What is the pH of \(0.100 M \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3} ?\)

What is the pH of \(1.00 M \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} ?\)

Sketch the titration curve (pH versus volume of \(0.50 M\) \(\mathrm{NaOH} \text { added })\) for a \(25 \mathrm{mL}\) sample of \(0.25 \mathrm{M} \mathrm{FeCl}_{3}\)

What is the difference between molar solubility and solubility product?

Give an example of how the common-ion effect limits the dissolution of a sparingly soluble ionic compound.

Which cation will precipitate first as a carbonate mineral from an equimolar solution of \(\mathrm{Mg}^{2+}, \mathrm{Ca}^{2+},\) and \(\mathrm{Sr}^{2+} ?\)

If the solubility of a compound increases with increasing temperature, does \(K_{\mathrm{sp}}\) increase or decrease?

The \(K_{\text {sp }}\) of strontium sulfate increases from \(2.8 \times 10^{-7}\) at \(37^{\circ} \mathrm{C}\) to \(3.8 \times 10^{-7}\) at \(77^{\circ} \mathrm{C} .\) Is the dissolution of strontium sulfate endothermic or exothermic?

Identify any of the following solids that are more soluble in acidic solution than in neutral water: \(\mathrm{CaCl}_{2}, \mathrm{Ba}\left(\mathrm{HCO}_{3}\right)_{2}\) \(\mathrm{PbSO}_{4}, \mathrm{Cu}(\mathrm{OH})_{2} .\) Explain your choices.

Tooth enamel is composed of a mineral known as hydroxyapatite, which has the formula \(\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3}(\mathrm{OH}) .\) Explain why tooth enamel can be eroded by acidic substances released by bacteria growing in the mouth.

Fluoride and Dental Hygiene Fluoride ions in drinking water and toothpaste convert hydroxyapatite in tooth enamel into fluorapatite: $$\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3}(\mathrm{OH})(s)+\mathrm{F}^{-}(a q) \rightleftharpoons \mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3} \mathrm{F}(s)+\mathrm{OH}^{-}(a q)$$ Why is fluorapatite less susceptible than hydroxyapatite to erosion by acids?

At a particular temperature, the \(\left[\mathrm{Ba}^{2+}\right]\) in a saturated solution of barium sulfate is \(1.04 \times 10^{-5} M .\) Starting with this information, calculate the \(K_{\mathrm{sp}}\) value of barium sulfate at this temperature.

If only \(0.160 \mathrm{g} \mathrm{Ca}(\mathrm{OH})_{2}\) dissolves in \(0.100 \mathrm{L}\) of water, what is the \(K_{\mathrm{sp}}\) value for calcium hydroxide at that temperature?

What are the equilibrium concentrations of \(\mathrm{Cu}^{+}\) and \(\mathrm{Cl}^{-}\) in a saturated solution of copper(I) chloride at \(25^{\circ} \mathrm{C} ?\)

What are the equilibrium concentrations of \(\mathrm{Pb}^{2+}\) and \(\mathrm{F}^{-}\) in a saturated solution of lead(II) fluoride at \(25^{\circ} \mathrm{C} ?\)

What is the solubility of calcite \(\left(\mathrm{CaCO}_{3}\right)\) in grams per milliliter at a temperature at which its \(K_{\mathrm{sp}}=9.9 \times 10^{-9} ?\)

Suppose you have 100 mL of each of the following solutions. In which will the most \(\mathrm{CaCO}_{3}\) dissolve? (a) \(0.1 M \mathrm{NaCl} ;\) (b) \(0.1 M \mathrm{Na}_{2} \mathrm{CO}_{3} ;\) (c) \(0.1 \mathrm{M} \mathrm{NaOH}\) (d) \(0.1 M \mathrm{HCl}\)

In which of the following solutions will \(\mathrm{CaF}_{2}\) be most soluble? (a) \(0.010 M \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2} ;\) (b) \(0.01 M \mathrm{NaF}\) (c) \(0.001 M\) NaF; (d) \(0.10 M \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\)

The average concentration of sulfate in surface seawater is about \(0.028 M .\) The average concentration of \(\mathrm{Sr}^{2+}\) is \(9 \times 10^{-5} M .\) Is the concentration of strontium in the sea significantly controlled by the insolubility of its sulfate salt?

Some scientists have proposed adding \(\mathrm{Fe}(\mathrm{III})\) compounds to large expanses of the open ocean to promote the growth of phytoplankton that would in turn remove \(\mathrm{CO}_{2}\) from the atmosphere through photosynthesis. Assuming the average pH of open ocean water is \(8.13,\) what is the maximum value of \(\left[\mathrm{Fe}^{3+}\right]\) in seawater if the \(K_{\mathrm{sp}}\) value of \(\mathrm{Fe}(\mathrm{OH})_{3}\) is \(1.1 \times 10^{-36} ?\)

Will calcium fluoride precipitate when \(125 \mathrm{mL}\) of \(0.375 M\) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) is added to \(245 \mathrm{mL}\) of \(0.255 M \mathrm{NaF}\) at \(25^{\circ} \mathrm{C} ?\)

Will lead(II) chloride precipitate if \(185 \mathrm{mL}\) of \(0.025 \mathrm{M}\) sodium chloride is added to \(235 \mathrm{mL}\) of \(0.165 M\) lead (II) perchlorate at \(25^{\circ} \mathrm{C} ?\)

A solution is \(0.010 M\) in both \(\mathrm{Br}^{-}\) and \(\mathrm{SO}_{4}^{2-} .\) A \(0.250 M\) solution of lead(II) nitrate is slowly added to it using a burette. a. Which anion will precipitate first? b. What is the concentration of the first anion when the second one starts to precipitate at \(25^{\circ} \mathrm{C} ?\)

Solution \(A\) is \(0.0200 M\) in \(A g^{+}\) ions and \(P b^{2+}\) ions. You have access to two other solutions: (B) \(0.250 M\) NaCl and (C) \(0.250 M\) aBr. a. Which solution, B or C, would be the better one to add to solution \(A\) to separate \(A g^{+}\) ions from \(P b^{2+}\) by selective precipitation? b. Using the solution you selected in part a, is the separation of the two ions complete?

A cook dissolves a teaspoon of baking soda (NaHCO \(_{3}\) ) in a cup of water and then discovers that the recipe calls for a tablespoon, not a teaspoon. If the cook adds two more teaspoons of baking soda to make up the difference, does the additional baking soda change the pH of the solution? Explain why or why not.

Antacid Tablets Antacids contain a variety of bases such as \(\mathrm{NaHCO}_{3}, \mathrm{MgCO}_{3}, \mathrm{CaCO}_{3},\) and \(\mathrm{Mg}(\mathrm{OH})_{2} .\) Only \(\mathrm{NaHCO}_{3}\) has appreciable solubility in water. a. Write a net ionic equation for the reaction of each base with aqueous HCl. b. Explain how substances sparingly soluble in water can act as effective antacids.

When silver oxide dissolves in water, the following reaction occurs: $$ \mathrm{Ag}_{2} \mathrm{O}(s)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow 2 \mathrm{Ag}^{+}(a q)+2 \mathrm{OH}^{-}(a q) $$ If a saturated aqueous solution of silver oxide is \(1.6 \times 10^{-4} M\) in hydroxide ion, what is the \(K_{\mathrm{sp}}\) of silver oxide?

Why does adding \(\mathrm{CaCl}_{2}\) to a \(\mathrm{HPO}_{4}^{2-} / \mathrm{PO}_{4}^{3-}\) buffer increase the ratio of \(\mathrm{HPO}_{4}^{2-}\) ions to \(\mathrm{PO}_{4}^{3-}\) ions?

Greenhouse Gases and Ocean pH Some climate models predict the pH of the oceans will decrease by as much as 0.77 pH unit due to increases in atmospheric carbon dioxide. a. Use the appropriate chemical reactions and equilibria to explain how increasing atmospheric \(\mathrm{CO}_{2}\) produces a decrease in oceanic pH. b. How much more acidic (in terms of \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\) ) would the oceans be if their \(\mathrm{pH}\) dropped this much? c. Oceanographers are concerned about the impact of a drop in oceanic pH on the survival of oysters. Why?

A pH 3.00 buffer is prepared by mixing solutions of nitrous acid and sodium nitrite. The total concentration of nitrous acid and sodium nitrate in the buffer is \(0.100 M\) Suppose 1.00 milliliter of \(1.00 M \mathrm{HCl}\) is added to a \(100 \mathrm{mL}\) sample of the buffer and 1.00 milliliter of \(1.00 M\) \(\mathrm{NaOH}\) is added to another \(100 \mathrm{mL}\) sample. In which sample would the addition of strong acid or base produce the greater change in \(\mathrm{pH}\) ? Explain your selection.

For each set of three acids, which one should you use to make a buffer with the given pH? a. Select from acetic acid \(\left(\mathrm{p} K_{2} 4.75\right),\) fluoroacetic acid \(\left(\mathrm{p} K_{\mathrm{a}} 2.59\right)\) and hypochlorous acid \(\left(\mathrm{p} K_{\mathrm{a}} 7.54\right)\) to make a buffer with a pH of 5.2. b. Select from formic acid \(\left(\mathrm{p} K_{2}=3.75\right),\) hypobromous acid \(\left(\mathrm{p} K_{\mathrm{a}}=7.54\right),\) and boric acid \(\left(\mathrm{p} K_{2} 9.27\right)\) to make a buffer with a pH of 8.0.

Estimate the \(K_{\mathrm{a}}\) values of the following indicators: a. Bromphenol blue, whose transition color occurs at a pH of about 3.8 b. Bromcresol green, whose transition color occurs at a \(\mathrm{pH}\) of about 4.3 c. Alizarin yellow \(\mathrm{R}\), whose transition color occurs at pH of about 10.9

Calculate the \(\mathrm{pH}\) at the equivalence point for the titration of \(10.0 \mathrm{mL}\) of \(0.100 M\) formic acid \(\left(K_{\mathrm{a}}=1.77 \times 10^{-4}\right)\) with \(0.100 M\) NaOH and for the titration of 10.0 mL of boric acid \(\left(K_{a 1}=5.4 \times 10^{-10}\right)\) with the same solution. Should the same indicator be used for both titrations?

In each of the following pairs of compounds, which is less soluble in water? a. \(\operatorname{AgI}\left(K_{\mathrm{sp}}=8.3 \times 10^{-17}\right)\) or \(\mathrm{AgCl}\left(K_{\mathrm{sp}}=1.8 \times 10^{-10}\right)\) b. \(\operatorname{Sr} \mathrm{F}_{2}\left(K_{\mathrm{sp}}=4.3 \times 10^{-9}\right)\) or \(\mathrm{MgF}_{2}\left(K_{\mathrm{sp}}=6.5 \times 10^{-9}\right)\) c. \(\mathrm{MnCO}_{3}\left(K_{\mathrm{sp}}=2.2 \times 10^{-1}\right) \mathrm{or} \mathrm{PbCO}_{3}\left(K_{\mathrm{sp}}=1.5 \times 10^{-13}\right)\)