Chapter 17

Does the pH of the solution increase, decrease, or stay the same when you (a) add solid ammonium chloride to a dilute aqueous solution of \(\mathrm{NH}_{3} ?\) (b) add solid sodium acetate to a dilute aqueous solution of acetic acid? (c) add solid NaCl to a dilute aqueous solution of \(\mathrm{NaOH}\)

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 \(0.015 \mathrm{M}\) oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} ?\) (b) add solid ammonium chloride to \(75 \mathrm{mL}\) of \(0.016 \mathrm{M} \mathrm{HCl} ?\) (c) add \(20.0 \mathrm{g}\) of \(\mathrm{NaCl}\) to \(1.0 \mathrm{L}\) of \(0.10 \mathrm{M}\) sodium acetate, \(\mathrm{NaCH}_{3} \mathrm{CO}_{2} ?\)

What is the \(\mathrm{pH}\) of the solution that results from adding \(25.0 \mathrm{mL}\) of \(0.12 \mathrm{M}\) HCl to \(25.0 \mathrm{mL}\) of \(0.43 \mathrm{M} \mathrm{NH}_{3} ?\)

Lactic acid \(\left(\mathrm{CH}_{3} \mathrm{CHOHCO}_{2} \mathrm{H}\right)\) is found in sour milk, in sauerkraut, and in muscles after activity. \(\left(K_{\mathrm{a}} \text { for lactic acid }=1.4 \times 10^{-4} .\right)\) (a) If \(2.75 \mathrm{g}\) of \(\mathrm{NaCH}_{3} \mathrm{CHOHCO}_{2}\), sodium lactate, is added to \(5.00 \times 10^{2} \mathrm{mL}\) of \(0.100 \mathrm{M}\) lactic acid, what is the \(\mathrm{pH}\) of the resulting buffer solution? (b) Is the \(\mathrm{pH}\) of the buffered solution lower or higher than the \(\mathrm{pH}\) of the lactic acid solution?

What mass of sodium acetate, \(\mathrm{NaCH}_{3} \mathrm{CO}_{2}\), must be added to 1.00 L of \(0.10 \mathrm{M}\) acetic acid to give a solution with a pH of \(4.50 ?\)

What mass of ammonium chloride, \(\mathrm{NH}_{4} \mathrm{Cl}\), must be added to exactly \(5.00 \times 10^{2} \mathrm{mL}\) of \(0.10 \mathrm{M} \mathrm{NH}_{3}\) solution to give a solution with a pH of 9.00?

Calculate the \(\mathrm{pH}\) of a solution that has an acetic acid concentration of 0.050 \(\mathrm{M}\) and a sodium acetate concentration of 0.075 M.

Which of the following combinations would be the best to buffer the pH of a solution at approximately \(9 ?\) (a) HCl and NaCl (b) \(\mathrm{NH}_{3}\) and \(\mathrm{NH}_{4} \mathrm{Cl}\) (c) \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) and \(\mathrm{NaCH}_{3} \mathrm{CO}_{2}\)

Which of the following combinations would be the best to buffer the pH of a solution at approximately \(7 ?\) (a) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\) (b) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\) and \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) (c) \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) and \(\mathrm{Na}_{3} \mathrm{PO}_{4}\)

Determine the volume (in mL) of \(1.00 \mathrm{M} \mathrm{NaOH}\) that must be added to \(250 \mathrm{mL}\) of \(0.50 \mathrm{M}\) \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) to produce a buffer with a pH of 4.50.

You dissolve \(0.425 \mathrm{g}\) of \(\mathrm{NaOH}\) in \(2.00 \mathrm{L}\) of a buffer solution that has \(\left[\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\right]=\left[\mathrm{HPO}_{4}^{2-}\right]= 0.132 \mathrm{M} .\) What is the \(\mathrm{pH}\) of the solution before adding NaOH? After adding NaOH?

What is the pH change when \(20.0 \mathrm{mL}\) of \(0.100 \mathrm{M}\) NaOH is added to \(80.0 \mathrm{mL}\) of a buffer solution consisting of 0.169 \(\mathrm{M} \mathrm{NH}_{3}\) and \(0.183 \mathrm{M} \mathrm{NH}_{4} \mathrm{Cl} ?\)

A titration of \(25.0 \mathrm{mL}\) of a solution of the weak base aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2},\) requires \(25.67 \mathrm{mL}\) of \(0.175 \mathrm{M}\) HCl to reach the equivalence point. $$\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}(\mathrm{aq})+\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \rightleftharpoons \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)$$ (a) What was the concentration of aniline in the original solution? (b) What are the concentrations of \(\mathrm{H}_{3} \mathrm{O}^{+}, \mathrm{OH}^{-}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}\) at the equivalence point? (c) What is the pH of the solution at the equivalence point?

Without doing detailed calculations, sketch the curve for the titration of \(30.0 \mathrm{mL}\) of \(0.10 \mathrm{M} \mathrm{NaOH}\) with 0.10 M HCl. Indicate the approximate pH at the beginning of the titration and at the equivalence point. What is the total solution volume at the equivalence point?

Without doing detailed calculations, sketch the curve for the titration of \(50 \mathrm{mL}\) of \(0.050 \mathrm{M}\) pyridine, \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}\) (a weak base), with 0.10 M HCl. Indicate the approximate \(\mathrm{pH}\) at the beginning of the titration and at the equivalence point. What is the total solution volume at the equivalence point?

Name two insoluble salts of each of the following ions. (a) \(\mathrm{Cl}^{-}\) (b) \(\mathrm{Zn}^{2+}\) (c) \(\mathrm{Fe}^{2+}\)

Name two insoluble salts of each of the following ions. (a) \(\mathrm{Cl}^{-}\) (b) \(\mathrm{Zn}^{2+}\) (c) \(\mathrm{Fe}^{2+}\)

Predict whether each of the following is insoluble or soluble in water. (a) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\) (b) \(\mathrm{Fe}(\mathrm{OH})_{3}\) (c) \(\mathrm{ZnCl}_{2}\) (d) CuS

For each of the following insoluble salts, (1) write a balanced equation showing the equilibrium occurring when the salt is added to water, and (2) write the \(K_{\text {sp expression. }}\) (a) \(\mathrm{AgCN}\) (b) \(\mathrm{NiCO}_{3}\) (c) \(\mathrm{AuBr}_{3}\)

For each of the following insoluble salts, (1) write a balanced equation showing the equilibrium occurring when the salt is added to water, and (2) write the \(K_{\text {sp }}\) expression. (a) \(\mathrm{PbSO}_{4}\) (b) \(\mathrm{BaF}_{2}\) (c) \(\mathrm{Ag}_{3} \mathrm{PO}_{4}\)

When \(1.55 \mathrm{g}\) of solid thallium(I) bromide is added to 1.00 L of water, the salt dissolves to a small extent. $$\operatorname{TiBr}(\mathrm{s}) \rightleftharpoons \mathrm{Tl}^{+}(\mathrm{aq})+\mathrm{Br}^{-}(\mathrm{aq})$$ The thallium(I) and bromide ions in equilibrium with TIBr each have a concentration of \(1.9 \times 10^{-3} \mathrm{M} .\) What is the value of \(K_{\mathrm{sp}}\) for TIBr?

At \(20^{\circ} \mathrm{C},\) a saturated aqueous solution of silver acetate, \(\mathrm{AgCH}_{3} \mathrm{CO}_{2}\), contains \(1.0 \mathrm{g}\) of the silver compound dissolved in \(100.0 \mathrm{mL}\) of solution. Calculate \(K_{\mathrm{sp}}\) for silver acetate. $$\mathrm{AgCH}_{3} \mathrm{CO}_{2}(\mathrm{s}) \rightleftharpoons \mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}(\mathrm{aq})$$

When \(250 \mathrm{mg}\) of \(\mathrm{SrF}_{2},\) strontium fluoride, is added to 1.00 L of water, the salt dissolves to a very small extent. $$\operatorname{SrF}_{2}(s) \rightleftarrows \operatorname{Sr}^{2+}(a q)+2 F^{-}(a q)$$ At equilibrium, the concentration of \(\mathrm{Sr}^{2+}\) is found to be \(1.03 \times 10^{-3} \mathrm{M}\). What is the value of \(K_{\mathrm{sp}}\) for \(\mathrm{SrF}_{2} ?\)

Calcium hydroxide, \(\mathrm{Ca}(\mathrm{OH})_{2},\) dissolves in water to the extent of 1.78 g per liter. What is the value of \(K_{\mathrm{sp}}\) for \(\mathrm{Ca}(\mathrm{OH})_{2} ?\) $$\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{s}) \rightleftharpoons \mathrm{Ca}^{2+}(\mathrm{aq})+2 \mathrm{OH}^{-}(\mathrm{aq})$$

You add 0.979 g of \(\mathrm{Pb}(\mathrm{OH})_{2}\) to \(1.00 \mathrm{L}\) of pure water at \(25^{\circ} \mathrm{C}\). The \(\mathrm{pH}\) is \(9.15 .\) Estimate the value of \(K_{\mathrm{sp}}\) for \(\mathrm{Pb}(\mathrm{OH})_{2}.\)

You place \(1.234 \mathrm{g}\) of solid \(\mathrm{Ca}(\mathrm{OH})_{2}\) in \(1.00 \mathrm{L}\) of pure water at \(25^{\circ} \mathrm{C}\). The pH of the solution is found to be \(12.68 .\) Estimate the value of \(K_{\mathrm{sp}}\) for \(\mathrm{Ca}(\mathrm{OH})_{2}.\)

What is the molar concentration of \(\mathrm{Au}^{+}(\mathrm{aq})\) in a saturated solution of AuCl in pure water at \(25^{\circ} \mathrm{C} ?\) $$\mathrm{AuCl}(\mathrm{s}) \rightleftarrows \mathrm{Au}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$$

The \(K_{\mathrm{sp}}\) value for radium sulfate, \(\mathrm{RaSO}_{4}\), is \(4.2 \times 10^{-11} .\) If \(25 \mathrm{mg}\) of radium sulfate is placed in \(1.00 \times 10^{2} \mathrm{mL}\) of water, does all of it dissolve? If not, how much dissolves?

Calculate the solubility, in moles per liter, of iron(II) hydroxide, \(\mathrm{Fe}(\mathrm{OH})_{2},\) in a solution buffered to a pH of 7.00.

Calculate the solubility, in moles per liter, of calcium hydroxide, \(\mathrm{Ca}(\mathrm{OH})_{2},\) in a solution buffered to a pH of 12.60.

Which insoluble compound in each pair should be more soluble in nitric acid than in pure water? (a) \(\mathrm{PbCl}_{2}\) or \(\mathrm{PbS}\) (b) \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) or \(\mathrm{AgI}\) (c) \(\mathrm{Al}(\mathrm{OH})_{3}\) or \(\mathrm{AgCl}\)

Which compound in each pair is more soluble in water than is predicted by a calculation from \(K_{\mathrm{sp}} ?\) (a) AgI or \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) (b) \(\mathrm{PbCO}_{3}\) or \(\mathrm{PbCl}_{2}\) (c) AgCl or AgCN

You have a solution that has a lead(II) ion concentration of 0.0012 M. If enough soluble chloride-containing salt is added so that the \(\mathrm{Cl}^{-}\) concentration is 0.010 \(\mathrm{M},\) will \(\mathrm{PbCl}_{2}\) precipitate?

You have \(95 \mathrm{mL}\) of a solution that has a lead(II) concentration of 0.0012 M. Will PbCl_ precipitate when 1.20 g of solid \(\mathrm{NaCl}\) is added?

Will a precipitate of \(\mathrm{Mg}(\mathrm{OH})_{2}\) form when \(25.0 \mathrm{mL}\) of 0.010 M NaOH is combined with 75.0 mL of a 0.10 M solution of magnesium chloride?

In each of the following cases, decide whether a precipitate will form when mixing the indicated reagents, and write a balanced equation for the reaction. (a) \(\mathrm{NaBr}(\mathrm{aq})+\mathrm{AgNO}_{3}(\mathrm{aq})\) (b) \(\mathrm{KCl}(\mathrm{aq})+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})\)

In each of the following cases, decide whether a precipitate will form when mixing the indicated reagents, and write a balanced equation for the reaction. (a) \(\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})\) (b) \(\mathrm{K}_{3} \mathrm{PO}_{4}(\mathrm{aq})+\mathrm{FeCl}_{3}(\mathrm{aq})\)

If you mix 48 mL of \(0.0012 \mathrm{M} \mathrm{BaCl}_{2}\) with \(24 \mathrm{mL}\) of \(1.0 \times 10^{-6} \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4},\) will a precipitate of \(\mathrm{BaSO}_{4}\) form?

Calculate the hydronium ion concentration and the pH of the solution that results when \(20.0 \mathrm{mL}\) of \(0.15 \mathrm{M}\) acetic acid, \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H},\) is mixed with \(5.0 \mathrm{mL}\) of \(0.17 \mathrm{M} \mathrm{NaOH}.\)

For each of the following cases, decide whether the 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 \(12 \mathrm{mL}\) of 0.015 M HCl. (c) 150 mL of \(0.20 \mathrm{M} \mathrm{HNO}_{3}\) is mixed with \(75 \mathrm{mL}\) of 0.40 M NaOH. (d) \(25 \mathrm{mL}\) of \(0.45 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) is mixed with \(25 \mathrm{mL}\) of 0.90 M NaOH.

Rank the following compounds in order of increasing solubility in water: \(\mathrm{Na}_{2} \mathrm{CO}_{3}, \mathrm{BaCO}_{3}\) \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\)

A sample of hard water contains about \(2.0 \times 10^{-3} \mathrm{M} \mathrm{Ca}^{2+} .\) A soluble fluoride- containing salt such as NaF is added to "fluoridate" the water (to aid in the prevention of dental cavities). What is the maximum concentration of \(\mathbf{F}^{-}\) that can be present without precipitating \(\mathrm{CaF}_{2} ?\)

Describe the effect on the pH of the following actions or explain why there is not an effect: (a) Adding sodium acetate, \(\mathrm{NaCH}_{3} \mathrm{CO}_{2}\), to \(0.100 \mathrm{M} \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) (b) Adding \(\mathrm{NaNO}_{3}\) to \(0.100 \mathrm{M} \mathrm{HNO}_{3}\)

What volume of 0.120 M NaOH must be added to \(100 .\) mL of \(0.100 \mathrm{M} \mathrm{NaHC}_{2} \mathrm{O}_{4}\) to reach a \(\mathrm{pH}\) of \(4.70 ?\)

What volume of 0.200 M HCl must be added to \(500.0 \mathrm{mL}\) of \(0.250 \mathrm{M} \mathrm{NH}_{3}\) to have a buffer with a pH of \(9.00 ?\)

Suppose you eat 28 grams of rhubarb leaves with an oxalic acid content of \(1.2 \%\) by weight. (a) What volume of \(0.25 \mathrm{M} \mathrm{NaOH}\) is required to titrate completely the oxalic acid in the leaves? (b) What mass of calcium oxalate could be formed from the oxalic acid in these leaves?

The \(\mathrm{Ca}^{2+}\) ion in hard water can be precipitated as \(\mathrm{CaCO}_{3}\) by adding soda ash, \(\mathrm{Na}_{2} \mathrm{CO}_{3} .\) If the calcium ion concentration in hard water is 0.010 \(\mathrm{M}\) and if the \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) is added until the carbonate ion concentration is 0.050 \(\mathrm{M},\) what percentage of the calcium ions has been removed from the water? (You may neglect carbonate ion hydrolysis.

You will often work with salts of \(\mathrm{Fe}^{3+}, \mathrm{Pb}^{2+}\) and \(\mathrm{Al}^{3+}\) in the laboratory. (All are found in nature, and all are important economically.) If you have a solution containing these three ions, each at a concentration of 0.10 M, what is the order in which their hydroxides precipitate as aqueous NaOH is slowly added to the solution?

Aniline hydrochloride, \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}\right) \mathrm{Cl}\), is a weak acid. (Its conjugate base is the weak base aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} .\) ) The acid can be titrated with a strong base such as NaOH. $$\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \rightleftharpoons \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)$$ Assume \(50.0 \mathrm{mL}\) of \(0.100 \mathrm{M}\) aniline hydrochloride is titrated with 0.185 M NaOH. (Ka for aniline hydrochloride is \(2.4 \times 10^{-5} .\) ) (a) What is the pH of the \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3}\right)\) Cl solution before the titration begins? (b) What is the \(\mathrm{pH}\) at the equivalence point? (c) What is the pH at the halfway point of the titration? (d) Which indicator in Figure 17.11 could be used to detect the equivalence point? (e) Calculate the pH of the solution after adding \(10.0,20.0,\) and \(30.0 \mathrm{mL}\) of base. (f) Combine the information in parts (a), (b), \((c),\) and \((e),\) and plot an approximate titration curve.

You have a solution that contains \(\mathrm{AgNO}_{3}\) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2},\) and \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} .\) Devise a separation method that results in having \(\mathrm{Ag}^{+}\) in one test tube, \(\mathrm{Pb}^{2+}\) in another, and \(\mathrm{Cu}^{2+}\) in a third test tube. Use solubility guidelines and \(K_{\mathrm{sp}}\) and \(K_{\mathrm{f}}\) values.