Lecture 16. Chem Equilibrium Part2

Lecture 16. Chem Equilibrium Part2 - Any Equilibrium...

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Unformatted text preview: Any Equilibrium Constant is Affected! Any K sp = APb AI2 = gPb [Pb ] (gI [I ]) Solubility of PbI2 in KNO3 solution. Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman 2+ - 2 Extended Debye-Hückel Equation Extended -0.51z 2 m log g = am 1+ 305 pm æ ö ç ÷ -0.51z 2 m ÷ ç ç a m÷ ç1 + ÷ ç ÷ 305 pm ø è -0.51z 2 m log g = 1 + a m 305 pm -0.51z 2 m 10 log g = g = 101 + a m 305 pm 10 log g = g = 10 Extended Debye-Hückel Equation Extended -0.51z 2 m log g = 1 + a m 305 pm -0.51z 2 m 10 log g = g = 101 + a m 305 pm 1 µ = å c iz 2 i 2i = 1 2 2 (c1z1 + c 2z 2 + ...) 2 Extended Debye-Hückel Equation Extended -0.51z 2 m log g = am 1+ 305 pm æ ö ç ÷ -0.51z 2 m ÷ ç ç a m÷ ç1 + ÷ ç ÷ 305 pm ø è 1 µ = å c iz 2 i 2i = 1 2 2 (c1z1 + c 2z 2 + ...) 2 10 log g = g = 10 e.g. e.g. => => aA+bB cC+dD c d c d AC AD [C]c gC [D]d gD K= a b = a b AA AB [A]a gA [B]b gB Extended Debye-Hückel Equation Extended e.g. e.g. => => aA+bB cC+dD c d c d AC AD [C]c gC [D]d gD K= a b = a b AA AB [A]a gA [B]b gB c d gC gD [C]c [D]d K= a b gA gB [A]a [B]b a b gA gB Kcd gC gD [C]c [D]d = K¢ = [A]a [B]b K’: a conditional formation constant (only applies under specific conditions, such as here for a given ionic strength) specific Why Does Ionic Strength Affect Solubility? Why Solubility of PbI2 in KNO3 solution. Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman What About More Complicated Equilibria? What LEVEL I Chem ical: Air Aerosols LEGEND EQU ILIBR IU M S oil Wa te r Suspended Sediment S edim ent Fish file:///C:/WINDOWS/Temporary%20Internet%20Files/Content.IE5/8XS1AV0L/261,3,Slide 3 What to do if You Lack the Information to What Calculate Activity Coefficients? (1) Dilution of the sample with water. Why? (2) Dilution of the sample with a concentrated salt solution. Dilution Why? Why? (3) Standard addition: Addition of calibration standard into the Standard sample. Why? sample. Charge Balance Charge ∑ [positive charges] = ∑ [negative charges] Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Mass Balance Mass The quantity of all species in a solution containing a The particular atom (or group of atoms) must equal the amount of that atom (or group) delivered to the solution. solution. Systematic Approach to Equilibrium Calculations Systematic Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. 2004. pH Dependence of CaF2 solubility pH Note the logarithmic ordinate. Daniel C. Harris, Exploring Chemical Analysis, 4th ed., W.H. Freeman and Company, New York, 2009. Freeman Fractional Composition Fractional Fractional composition of an acid HA Fractional with pKa = 5.0. with Daniel C. Harris, Exploring Chemical Analysis, 4th ed., W.H. Freeman and Company, New York, 2009. Freeman Fractional Composition Fractional H + ] [ A- ] [ Ka = Þ [HA] A- ] [ + HA] [H ] [ = Ka [A ] 1 = = [ A ] + [HA] 1 + [HA] 1 + A- ] [ or simplified : Ka = A ] + [HA] K a + [H + ] [ A- ] [ 1 = [HA] 1+ A- ] [ 1 H+] [ Ka Fractional Composition Fractional Example: Solubility of CaF2 in Water and 0.1 M NaCl Example: What is the difference in solubility of CaF2 in water and in 0.1 M NaCl? Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Daniel Freeman and Company, New York, 2001. Freeman Example: Solubility of CaF2 in Water and 0.1 M NaCl Example: What is the difference in solubility of CaF2 in water and in 0.1 M NaCl? ⇒Activity coefficients predict a 62% higher solubility in 0.1 M Activity NaCl than in pure water. ⇒Prove this to yourself! ...
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