Chem302_Laude_Exam2_Spring09

Chem302_Laude_Exam2_Spring09 - Version 041 Exam 2 Laude...

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Unformatted text preview: Version 041 Exam 2 Laude (52390) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. K a = [ H + ] [ A ] [ HA ] pK a =- log K a pH =- log [H + ] pOH =- log [OH ] [ OH ] = ( K b C b ) 1 / 2 [ OH ] = K b parenleftbigg C b C a parenrightbigg 10 14 = K w [H + ] [OH ] = K w K a K b = K w pK a + pK b = pK w 14 = pK w ( K a C a ) 1 / 2 = [ H + ] K a parenleftbigg C a C b parenrightbigg = [ H + ] [ H + ] = ( K ax K ay ) 1 / 2 pH = 0 . 5( pK ax + pK ay ) 0 = [ H + ] 2- C a [ H + ]- K w K sp = [ C ] c [ A ] a E o cell = E o cathode- E o anode E cell = E o cell- parenleftbigg . 05916 n parenrightbigg log Q Q = [ C ] c [ D ] d [ A ] a [ B ] b G o =- n F E o cell =- R T ln K E o cell = parenleftbigg R T ln K n F parenrightbigg parenleftbigg I t n F parenrightbigg = moles of product Half reaction E o Au 3+ + 3 e - Au +1 . 50 Cl 2 + 2 e - 2 Cl +1 . 36 Ag + + e - Ag +0 . 80 O 2 + 2 e + 2 H+- H 2 O 2 +0 . 68 I 2 + 2 e - 2 I +0 . 53 Pb 2+ + 2 e - Pb- . 13 Ni 2+ + 2 e - Ni- . 25 Mn 2+ + 2 e - Mn- 1 . 12 Na + + e - Na- 2 . 71 Sr 2+ + 2 e - Sr- 2 . 89 F = 96 , 485 . 3 C per mole of e 1 Ampere = 1 C s 1 R = 8 . 314 J mol 1 K 1 N = 6 . 022 10 23 001 6.0 points Consider a tetraprotic acid of the form H 4 A. If a buffer is formed by placing Li 2 H 2 A and Li 3 HA in solution, which K a is used to solve the buffer equation? 1. K a 2. K a 4 3. K a 1 4. not enough information 5. K a 3 correct 6. K a 2 Explanation: The two salts when dissolved in water will yield H 2 A 2 and HA 3 . These two species are related by K a 3 . 002 6.0 points What would be the pH of a solution pre- pared from 200 mL of 5 M HOBr and 200 mL of 1 M NaOBr? The K a of hypobromous acid is 2 10 9 . 1. 7 2. 10 3. 6 4. 4 5. 8 correct Explanation: Version 041 Exam 2 Laude (52390) 2 [H + ] = K a ( C a /C b ) = ( 2 10 9 ) (2 . 5 M /. 5 M) = 10 8 pH = 8 003 6.0 points Consider 4 L of a buffer composed of 2 M HCN and 3 M NaCN? How many moles of strong acid could this buffer withstand? 1. 2 2. 8 3. 3 4. 12 correct 5. Explanation: Any added strong acid will react with the weak base that is present (in this case CN-), of which there are 12 moles (4 L x 3 M = 12 moles). 004 6.0 points If one added 20 mL of 0 . 04 M Ba(OH) 2 to 100 mL of a buffer composed 0 . 1 M acrylic acid and 0 . 05 M sodium acrylate, what would be the pH of the resulting solution? Acrylic acid has K a 5 . 6 10 5 . 1. 4.37 2. 3.78 3. 4.55 4. 4.15 correct 5. 3.95 Explanation: The general reaction that takes place is: HA + OH A + H 2 O Initial amounts of each species are 0.01, .0016 and 0.005 moles respectively. After the re- action goes to completion, the equilibrium amounts are 0.0084, 0 and 0.0066 moles re-amounts are 0....
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Chem302_Laude_Exam2_Spring09 - Version 041 Exam 2 Laude...

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