# 2 b has pk a1 375 and pk a2 828 acid hq has a pk a

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2 B + has pK a1 = 3.75 and pK a2 = 8.28. Acid HQ has a pK a = 4.07. Write the chemical equilibrium and the equilibrium constant (in scientific notation) for the following situations (a-d): a) a 0.100 M solution of H 2 B + H 2 B + HB + H + K a1 = 10 -3.75 = 1.8 x 10 -4 b) half the equivalence volume of LiOH has been added to solution a) H 2 B + + OH - HB + H 2 O K= 1/K b2 = K a1 /K w 10 -3.75 /10 -14 = 1.8 x 10 10 c) 25 ml of 0.100 M HCl is mixed with 50 mL of 0.100 M LiQ H + + Q - HQ K= 1/K a = 1/10 -4.07 = 1.2 x 10 4 d) 25 ml of 0.100 M H 2 B + is mixed with 50 mL of 0.100 M LiQ H 2 B + + Q - HB + HQ K = K a (H 2 B + )/K a (HQ) = 10 -3.75 /10 -4.07 = 10 0.32 K = 2.1 e) Rank from highest to lowest concentration the forms of H 2 B + in a solution with a pH = 7.0 HB > B - > H 2 B +

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5. (30 pts) For H 2 A K a1 = 1.00 x 10 -4 and K a2 = 1.00 x 10 -9 . a) Find the pH and concentrations of H 2 A, HA - and A 2- for a 0.050 M Na 2 A solution. A 2- + H 2 O OH - + HA - K b1 =K w /K a2 = 1.00 x 10 -5 init .050 equil .050-x x x K b = x 2 /(.05-x) x = [OH - ] = [HA - ] = 7.0 x 10 -4 M [H + ] = K w /[OH - ] = 1.43 x 10 -11 pH = 10.85 [A 2- ] = .050-7.02 x 10 -4 = .049 M = + 1 a 2 K ] HA ][ H [ = A] [H 1.0 x 10 -10 M b) Find the pH and concentrations of H 2 A, HA - and A 2- for a 0.050 M LiHA solution. HA - A 2- + H + HA - + H 2 O OH - + H 2 A F + K K K + F K K = ] H [ a1 w a1 a2 a1 1/2 + = 3.16 x 10 -7 M pH = 6.50 [HA - ] = 0.050 M = + 1 a 2 K ] HA ][ H [ = A] [H 1.6 x 10 -4 M = + ] H [ ] HA [ K = ] [A 2 a 2 1.6 x 10 -4 M 6. (10pts) Find the pH and fraction of dissociation of a 0.0500 M solution of a weak acid with K a = 1.00 x 10 -5 . HZ Z - + H + Init. 0.050 0 0 Equil. 0.050-x x x K a = x 2 /(.05-x) x = [H + ] = 7.02 x 10 -4 pH = 3.154 α = x/F = K a /(K a + [H + ]) = 1.40 x 10 -2
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