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Unformatted text preview: + donation : H 3 A Three equilibria : k a1 , k a2 , k a3 Example : H 3 PO 4 Diprotic Acids H 2 A(aq) + H 2 O(l) H 3 O + (aq) + HA (aq) K a1 HA (aq) + H 2 O(l) H 3 O + (aq) + A 2 (aq) K a2 H 2 A H 3 O + HA A 2 [Initial] a 0 0 [Change] x +x+y +xy +y [Equilib.] ax +x+y +xy +y Double Equilibrium Two equations two unknowns K a1 = K a2 = Can simplify when K a2 << K a1 Use weak acid approach and proceed stepwise. x 2 y 2 a x y (x + y) x y 3 Example Calculate the pH of a 0.1 M solution of H 2 S given that K a1 = 1.3 x 10 7 and K a2 = 7.1 x 10 15 . Example Calculate the concentration of all components of a 0.01 M H 3 PO 4 solution given that K a1 = 7.6 x 10 3 , K a2 = 6.2 x 10 8 , and K a3 = 2.1 x 10 13 ....
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This note was uploaded on 04/23/2008 for the course CHEM 2B taught by Professor Clemens during the Winter '08 term at UC Davis.
- Winter '08