09_Complex_Acid-Base_Titrations-page2

# 09_Complex_Acid-Base_Titrations-page2 - KA1 KA2 = 7.5x10-3...

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Unformatted text preview: KA1 / KA2 = 7.5x10-3 / 6.0x10-8 = 1.25 x 105 KA2 / KA3 = 6.0x10-8 / 4.8x10-13 = 1.25 x 105 This indicates that it is possible to treat each step separately during a titration. Just because you have a material where KA1/KA2 is not greater than 1000 does not mean it can’t be titrated. We’ll now review the calculations involved for the titration of a ‘well behaved’ diprotic acid. It is still possible to determine equilibrium concentrations at any point during a titration. This really is nothing more that doing two separate sets of calculations. However, when KA1/KA2 < 1000, you don’t get a sharp ‘first’ endpoint. You can Titrate to the ‘final endpoint’ Titrate to a form where Kx/KY > 1000. Triprotic acids (or higher) simply amount to repeating the process as many times as necessary. Construct a curve for the titration of 25.00 ml of 0.1000 M sodium carbonate (Na2CO3) with 0.1000 M HCl. KB1 = 2.00 x 10-4 = [ OH- ] [ CO32- ] [HCO3- ] KB2 = 2.51 x 10-8 = [ OH ] [HCO3 ] [ H2CO3 ] KB1 / KB2 = 8.00 x so our base is ‘well behaved’ and we can treat each equilibrium separately. 103 KB1 = 2.00 x 10-4 = [ OH- ] [ CO32- ] [HCO3- ] [ OH- ] = [ CO32- ] [ HCO3- ] = 0.1000M - [ CO32- ] ...
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