Old exam 2B

Old exam 2B - ANSWER KEY Seat Chemistry 241 Exam 2 May 28,...

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ANSWER KEY Seat - Chemistry 241 Exam 2 May 28, 2008 Honor Pledge: I have neither given nor received help on this exam, nor have I seen anyone else do so. Signed:__________________________________ 1. 2. 3. 4. 5. 6. 7. Total _______ 15 10 20 10 20 10 15 100 SHOW YOUR WORK (including equilibria reactions) CIRCLE NUMERICAL ANSWERS 1. 9-37 (15pts) The pH of a 0.0100 F solution of a base, Z, is 11.291. a) What is the pK a of the conjugate acid of Z? 4 3 2 3 2 10 75 . 4 10 95 . 1 0100 . ) 10 95 . 1 ( ] [ ] ][ [ + × = × × = = = x F x Z HZ OH K b 11 10 11 . 2 × = = b w a K K K pK a = 10.676 b) How many milliliters of 0.246 M HNO 3 (a strong acid) should be added to 213 mL of a 0.00666 M solution of Z to give a solution pH of 10.25. Z + H + ZH + Z= (.213L)(6.66 x 10 -3 M) = 1.42 x 10 -3 moles init 1.42 x 10 -3 x pK a = 10.676 equil. 1.42 x 10 -3 – x 0 x [Acid] [Base] log + pK = pH a [] x x + = ] 10 42 . 1 [ log 676 . 10 25 . 10 3 × X = 1.0 x 10 -3 1.01 x 10 -3 moles/ .246 M = 4.1 x 10
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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 2B - ANSWER KEY Seat Chemistry 241 Exam 2 May 28,...

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