L4 - Chemistry 15 Lecture 4 Acid-Base Equilibria I a)...

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Chemistry 15 February 4, 2008 Lecture 4 Acid-Base Equilibria I a) Brønsted definition of acids and bases: Acid is a proton donor: 23 HA H O H O A + + + R Base is a proton acceptor: 2 B HO BH OH + ++ R b) Conjugated acid-base pairs: HA & A - , H 3 O + & H 2 O, BH + & B, H 2 O & OH - c) Autoprotolysis of water: 22 3 HO HO HO + R ; 3 [] [ ] w KH O O H +− = d) Acid and base dissociation constants; for any conjugated acid/base pair: ab w KK K × = e) Calculation of the pH of a weak acid solution (1) acid dissociation: HA H O H O A + + + R ; 3 [ ] a HO A K HA + = (2) water autoprotolysis: 3 [ ] w O O H + = (3) charge balance equation: 3 [ ] [ ] A + −− =+ (4) mass (material) balance equation: [ ] HA FH A A (5) from (3) 3 [][ ] [ ] A −+ ⇒= (6) from (4) [ ] HA HA F A and using (5): 3 [ ] [ ] HA HA F H O OH =− + thus (1) 2 33 3
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