13Solub - SOLUBILITY Solubility: quantity of a substance...

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Unformatted text preview: SOLUBILITY Solubility: quantity of a substance that dissolves to form a saturated solution Solubility: g/L Molar solubility: mole/L Some salts are very soluble (> 0.1 M). Recall solubility rules. Some salts are sparingly soluble (< 0.1 M) sometimes referred to as `insoluble'. Precipitation and Solubility of ionic salts and their equilibrium in water MA(s) M+(aq) + A-(aq) SOLUBILITY EQUILIBRIA Precipitation Ag+(aq) + Cl-(aq) AgCl(s) Dissolution AgCl(s) Ag+(aq) + Cl-(aq) When forward rate = backward rate: equilibrium AgCl(s) Ag+(aq) + Cl-(aq) The concentration of solid does not change at equilibrium SOLUBILITY Solubility Product: Ksp AgCl AgBr AgI CdS ZnS Mg(OH)2 Ca(OH)2 CaF2 BaCO3 BaSO4 1.8 x 10-10 5.0 x 10-13 8.3 x 10-17 8.0 x 10-27 1.1 x 10-21 1.8 x 10-11 5.5 x 10-6 3.9 x 10-11 5.1 x 10-9 1.1 x 10-10 SOLUBILITY CALCULATION Calculate [Ca2+] and [F-] for a saturated CaF2 solution. CaF2 (s) Ca+2 (aq) +2F- (aq) Ksp = [Ca2+][F-]2 =3.9 x 10-11 at 25oC What is the solubility? solubility = amount of CaF2 dissociated COMMON ION EFFECT SOLUBILITY CALCULATION Common Ion Effect What is the solubility of CaF2 in 0.01 M NaF solution? Ksp = 3.9 x 10-11 CaF2 solubility = [Ca2+] = x [F-] = 0.01 M CaF2(s) Initial Ca2+(aq) + 2F-(aq) AgCl(s) Ag+(aq) + Cl-(aq) Add [Ag+] to solution at equilibrium Final Add [Cl-] to solution at equilibrium Effect of pH What is the solubility of Mg(OH)2? Effect of pH 1. Milk of Magnesia Mg(OH)2 MgCl2 + 2NaOH Mg(OH)2 + 2NaCl What is the solubility of Mg(OH)2 in a solution with a pH of 9? 2. Barium salts BaCl2 + 2NaOH Ba(OH)2 + 2OH- Effect of pH 2. Barium salts (continued) BaCl2 + 2 Na2CO3 BaCO3(s) + 2NaCl BaCO3(s) Ba+2(aq) + CO32-(aq) Effect of pH Barium salts (continued) BaCl2 + 2 Na2SO4 BaSO4(s) + 2NaCl BaSO4(s) Ba+2(aq) + SO42-(aq) Effect of pH on common ions If either the anion or the cation is involved in an acid base equilibrium, then it is a common ion problem. Basic Metal hydroxides Low pH increases solubility Example Mg(OH)2 Salts of weakly basic anion Low pH increases solubility Examples Mg(HCO3)2 ZnCO3 Contrast with CaSO4 Ca3(PO4)2 NaF Basic anion: anion which reacts with water to produce OH-: it hydrolyzes water. anion that is a proton acceptor Sample Problem Will Mn(OH)2 precipitate from 0.05 M MnCl2 solution if the pH = 8? Ksp = [Mn2+][OH-]2 = 1.9 x 10-13 AMPHOTERISM Amphoterism is the ability of a molecule to act both as an acid and as a base. This results in metal hydroxides which are soluble in both acids and bases. Hydration: Al3+(aq) Al(H2O)63+ Al(OH)3(s) + 3H2O In acid: Al(OH)3(OH2)3 + H+ In base: Al(OH)3(OH2)3 + OH- Al(OH)4(OH2)2-(aq) + H2O solubility increases. Al(OH)3(OH2)3(s) Al(OH)2(OH2)4+(aq) solubility increases. ALUMINUM SOLUBILITY DEMO Al(NO3)3(s) + H2O Al3+(aq) + 3NO3-(aq) 1. Hydration: Al3+(aq) Al(H2O)63+ Add Base: Al(H2O)63+ + 3OH- Al(OH)3(H2O)3(s) 2. Add acid: Al(OH)3(H2O)3 + H+ Al(OH)2(OH2)4+(aq) Solubility increases. 3. Add Base Al(OH)3(H2O)3 +OH- Al(OH)4(H2O)2-(aq) + H2O Solubility increases. AMPHOTERIC METAL HYDROXIDES There are amphoteric hydroxides of Al3+ Cr3+ Zn2+ Sn2+ Many transition metal ions These involve formation of complex ions, such as: Al(OH)3(OH2)3 + H+ Al(OH)2(OH2)4+ + OH- Al(OH) (OH ) - 4 2 2 FORMATION OF COMPLEX IONS Hydration of metal ions Cu2+(aq) + 4 H2O(l) [Cu(OH2)4]2+(aq) Lewis Acid + Lewis Lewis Acid/Base Base Adduct = Metal Complex Cu2+(aq) Cu(H2O)42+ Other Lewis bases react with metal ions to form complexes Cu2+(aq) + 4 NH3(aq) [Cu(NH3)4]2+(aq) Cu2+(aq) + 4 CN-(aq) [Cu(CN)4]2-(aq) Cu2+(aq) + 4 Cl-(aq) [Cu(Cl)4]2-(aq) Amphoteric hydroxides Low and high pH increases solubility Al(OH)3 Cr(OH)3 Zn(OH)3 Sn(OH)2 other transition metal hydroxides METAL COMPLEX STABILITY Cu(OH2)42+ + 4NH3 Cu(NH3)42+ + 4H2O Cu2+(aq) + 4NH3 Cu(NH3)42+ + 4H2O [H2O] = constant Complex Ion Formation What is the [Cu2+ (aq)] in 1 lit. solution that has 1 x10-3 moles of Cu2+ ions (free ions + complex ions) and that is 0.1 M in NH3 at equilibrium? Kf = 5 x 1012 Cu2+(aq) + 4 NH3(aq) Cu(NH3)42+(aq) Kf VALUES OF SOME COMPLEXES Ag(NH3)2+ Cu(NH3)42+ Cu(CN)42Ag(CN)2Ag(S2O3)231.7 x 107 5 x 1012 1 x 1025 1 x 1021 2.9 x 1013 Water Chemistry (Ch. 18.5-6) Complex Ion Formation CuCO3 is a sparingly soluble salt? Ksp CuCO3 = 2.3 x 10-10 Water in State College/UP Campus Predominantly well water 23 wells + 1 open reservoir [Ca2+ ] 165-185 ppm 10-15 ppm Mixed to reduce water hardness Cl2 injected to kill bacteria F- added Alum (K2SO4.Al2(SO4)3.24H2O) added to improve clarity NaOH added to neutralize pH How can I get it to dissolve? What is the equilibrium constant for the following reaction? CuCO3(s) + 4NH3(aq) CO32-(aq) + [Cu(NH3)4]2+(aq) Ksp CuCO3 = 2.3 x 10-10 Kf [Cu(NH3)4]2+ = 5 x 1012 Remediation of Water Ca2+ (hard water), Pb2+ (toxic) are precipitated by CO32Ksp CaCO3 PbCO3 8.7 x 10-9 3.3 x 10-14 Which compound(s) could we use to supply CO32-? How much do we need to add ? ...
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