4 General Chemistry: Chapter 19 Ksp vs. activitiesWhen the solubility of the salt is very low the activity coefficients, g of the ions in solution are nearly equal to one. The activity of a pure solid is, by definition, equal to one. By setting activity coefficients of the ions in solution precisely to one the solubility product expression can be obtained: a(Ca2+) = g[Ca2+] and g = 1 thus a(Ca2+) = [Ca2+]General Chemistry: Chapter 19
5 General expression for Ksp For AaBb aAb+ + bBa- dissociation the Ksp = [A]a[B]b,where a and b are the stoichiometric constants and the electrical charges omitted for simplicity of notation.General Chemistry: Chapter 19
6 Ksp values in Table 16 at 25 °C Compounds KspAgBr ↔ Ag+ + Br-7.7 10-13CuBr ↔ Cu+ + Br-4.9 10-9Hg2Br2 ↔ 2 Hg+ + 2Br-4.6 10-23PbBr2 ↔ Pb2+ + 2 Br-7.4 10-5Ag2CO3 ↔ 2 Ag+ + CO32-6.5 10-12BaCO3 ↔ Ba2+ + CO32-CaCO3 ↔ Ca2+ + CO32-4.8 10-9You will find many more values in the Table 16General Chemistry: Chapter 19
7 General Chemistry: Chapter 19 Several examplesSilver bromideSilver carbonateLead(II) iodidepartially oxidizedGeneral Chemistry: Chapter 19
9 The general formula for solubility Chemistry 140 Fall 2002The general formula for solubilityFor AaBb aAb+ + bBa- dissociation: Ksp = [A]a[B]bNotice that [A] = a S, [B] = b S andGeneral Chemistry: Chapter 19
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