In: Chemistry
Given the following information about Fe in aqueous solutions, what will be the ratio of (Fe(OH)2+) to (Fe(OH)30) in solution at pH 6.0, 6.5, 7.0, 7.5, 8.0, 8.5?
Fe3+ + 2H2O = Fe(OH)2+ +2H+ logK = -5.7
Fe3+ + 3H2O = Fe(OH)30 + 3H+ logK = -13.1
Fe3+ + 2H2O = Fe(OH)2+ +2H+ logK = -5.7
K = [Fe(OH)2+ ][H+ ]^2/[Fe3+ ] k = 10^(-5.7)
[Fe(OH)2+ ] = K[Fe3+ ] / [H+ ]^2
Fe3+ + 3H2O = Fe(OH)30 + 3H+ logK1 = -13.1
K1 = [ Fe(OH)30 ][H+ ]^3/[Fe3+ ] k1 = 10^(-13.1)
[ Fe(OH)30 ] = K1[Fe3+ ]/[H+ ]^3
therefore
[Fe(OH)2+ ]/[ Fe(OH)30 ] = K [H+ ]/ K1
at pH = 6 [H+] = 10^(-6)
[Fe(OH)2+ ]/[ Fe(OH)30 ] = (10^(-5.7)*10^(-6))/ (10^(-13.1))
[Fe(OH)2+ ]/[ Fe(OH)30 ] = 25.12
at pH = 6.5
[Fe(OH)2+ ]/[ Fe(OH)30 ] = (10^(-5.7)*10^(-6.5))/ (10^(-13.1))
[Fe(OH)2+ ]/[ Fe(OH)30 ] = 7.94
At pH = 7.0
[Fe(OH)2+ ]/[ Fe(OH)30 ] = (10^(-5.7)*10^(-7))/ (10^(-13.1))
[Fe(OH)2+ ]/[ Fe(OH)30 ] = 2.511
at pH= 7.5
[Fe(OH)2+ ]/[ Fe(OH)30 ] = (10^(-5.7)*10^(-7.5))/ (10^(-13.1))
[Fe(OH)2+ ]/[ Fe(OH)30 ] = 0.794
at pH = 8
[Fe(OH)2+ ]/[ Fe(OH)30 ] = (10^(-5.7)*10^(-8))/ (10^(-13.1))
[Fe(OH)2+ ]/[ Fe(OH)30 ] = 0.2511
at pH = 8.5
[Fe(OH)2+ ]/[ Fe(OH)30 ] = (10^(-5.7)*10^(-8.5))/ (10^(-13.1))
[Fe(OH)2+ ]/[ Fe(OH)30 ] = 0.0794