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Quiz 3-solutions

# Quiz 3-solutions - Version 260 Quiz 3 Laude(52390 This...

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Version 260 – Quiz 3 – Laude – (52390) 1 This print-out should have 8 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. pH = - log [H + ] pOH = - log [OH - ] K w = 10 - 14 [H + ][OH - ] = K w K a K b = K w [H + ] = K a ( C a /C b ) pH = p K a + log( C b /C a ) [OH - ] = K b ( C b /C a ) pOH = p K b + log( C a /C b ) [H + ] = ( K ax K ay ) 1 / 2 pH = 0 . 5(p K ax + p K ay ) 001 5.0 points What would be the pH of a 1 M solution of Na 2 HPO 4 ? Assume H 3 PO 4 has a p K a 1 of 2 and a p K a 2 of 7 and a p K a 3 of 13. 1. 4.5 2. 2 3. 13 4. 10 correct 5. 7 6. 7.5 Explanation: For a solution composed of a single ampho- teric species (HPO 4 2 - ), pH = 0 . 5(p K a 2 + p K a 3 ) = 0 . 5(7 + 13) = 10 002 5.0 points One liter of a buffer containing 2 M H 2 CO 3 and 1 . 5 M NaHCO 3 has 24 g of LiOH added to it. What is the new pH? Assume the K a 1 of H 2 CO 3 is 2 . 5 × 10 - 4 . 1. 6 2. 3 3. 11 4. 4 correct 5. 10 6. 8 Explanation: (24 g LiOH) parenleftbigg 1 mol 24 g parenrightbigg = 1 mol LiOH [H + ] = K a ( C a /C b ) = ( 2 . 5 × 10 - 4 ) (1 M / 2 . 5 M) = 10 - 4 pH = 4 003 5.0 points A 1 M solution of NaOH is used to titrate a 1 M solution of C 6 H 5 COOH (benzoic acid). If the

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