Old exam 2A

Old exam 2A - Answer Key Seat Chemistry 241 Exam 2 February...

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Answer Key Seat - Chemistry 241 Exam 2 February 11, 2009 Honor Pledge: I have neither given nor received help on t his e xam, nor ha ve I seen anyone else do so. Signed:________________________________ 1. 2. 3. 4. 5. 6. 7. Total _______ 16 9 30 10 15 10 10 100 SHOW YOUR WORK (including equilibria reactions) CIRCLE NUMERICAL ANSWERS 1. (16 pts) The diprotic acid H 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 calculate the equilibrium constant (in scientific notation) for the following situations: a) a 0.100 M solution of NaB H 2 O + B - HB + OH- K b1 = K w / K a2 10 -14 /10 -8.28 = 1.9 x 10 -6 b) half the equivalence volume of HCl is added to solution a) B - + H+ HB + K= 1/K a2 = 10 8.28 = 1.9 x 10 8 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
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This note was uploaded on 01/09/2011 for the course CHEM 241 taught by Professor Tiani during the Summer '08 term at UNC.

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Old exam 2A - Answer Key Seat Chemistry 241 Exam 2 February...

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