Soluble nontoxic salts such as Fe₂(SO₄)₃ are often used during water purification to remove soluble toxic contaminants, because they form gelatinous hydroxides that encapsulate the contaminants and allow them to be filtered from the water.

(a) Calculate the molar solubility in water of Fe(OH)₃ at 25°C.

(b) What is the concentration of hydroxide ions in a saturated solution of Fe(OH)₃? Calculate the pH of the solution.

(c) Discuss whether your result in part (b) is reasonable for a solution of a basic hydroxide. Explain what assumptions were made in your calculations and evaluate the validity of the assumptions.

(d) A simplified equation for the reaction of Fe³⁺ ions with water is Fe³⁺(aq) + 6 H₂O(l) ⇌ Fe(OH)₃(s) + 3 H₃O⁺(aq). Use the data in Table 6I.1 and Kw to calculate the equilibrium constant for this reaction.

(e) If 10.0 g of Fe₂(SO₄)₃ is dissolved in enough water to make up 1.00 L of aqueous solution and the pH of the solution is raised to 8.00 by addition of NaOH, what mass of solid Fe(OH)₃ will form?

(f) To test for the ability of Fe₂(SO₄)₃ to remove chloride ions from water, a standard aqueous solution containing 24.72 g of NaCl in 1.000 L of solution was prepared. A sample of the NaCl solution of volume 25.00 mL was then combined with the mixture described in part (e) and stirred. The Fe(OH)₃ precipitate containing encapsulated chloride ion was removed by filtration, then dissolved in acid. An aqueous solution of AgNO₃ was then added to the resulting solution and the solid AgCl formed filtered and dried. The mass of AgCl was 0.604 g. What percentage of the chloride ion in the sample had been removed from the solution?

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TABLE 61.1 Solubility Products at 25 °C Compound aluminum hydroxide antimony sulfide barium carbonate fluoride sulfate bismuth sulfide calcium carbonate fluoride hydroxide sulfate chromium(III) iodate copper(1) bromide chloride iodide sulfide copper(II) iodate oxalate sulfide iron(II) hydroxide sulfide iron (III) hydroxide lead(II) bromide chloride Formula AI(OH)3 Sb₂S3 BaCO3 BaF₂ BaSO4 Bi₂S3 CaCO, CaF₂ Ca(OH)2 CaSO4 Cr(103)3 CuBr CuCl Cul Cu₂S Cu(IO3)2 CuC₂04 Cus Fe(OH)2 FeS Fe(OH)3 PbBr₂ PbCl₂ Ksp 1.0 × 10-33 1.7 x 107 8.1 x 10 9 -93 1.7 x 10-6 1.1 X 10-10. 1.0 × 10-97 8.7 x 10-9 -11 4.0 X 107 5.5 x 10-6 2.4 x 10-5 5.0 x 10-6 4.2 x 10-8 1.0 x 10-6 5.1 x 10-12 2.0 × 10-47 1.4 x 10-7 2.9 × 10-8 1.3 × 10-36 1.6 X 10-14 6.3 x 10-¹ 2.0 × 10-3⁹ -18 7.9 X 10-5 1.6 x 10-5 Compound lead(II) fluoride iodate iodide sulfate sulfide magnesium ammonium phosphate carbonate fluoride hydroxide mercury(I) chloride iodide mercury(II) sulfide, black sulfide, red nickel(II) hydroxide silver bromide carbonate chloride hydroxide iodide sulfide zinc hydroxide sulfide Formula PbF₂ Pb(103)2 Pbl₂ PbSO₁ Pbs MgNH₂PO4 MgCO3 MgF₂ Mg(OH)2 Hg₂Cl₂ Hg₂l₂ Hgs HgS Ni(OH)₂ AgBr Ag₂CO3 AgCl AgOH AgI Ag₂S Zn(OH)₂ ZnS Ksp 3.7 x 10-8 2.6 X 10-13 -8 1.4 X 108 1.6 x 10-8 8.8 x 10-29 2.5 X 10-13 1.0 x 10-5 6.4 X 10 1.1 X 10-¹1 2.6 X 10-18 1.2 x 10-28 1.6 x 10-52 1.4 x 10-53 6.5 X 10-18 7.7 x 10-13 6.2 x 10-12 1.6 X 10-10 1.5 X 10-8 8 x 10-17 6.3 x 10-51 2.0 × 10-¹7 1.6 x 10-24