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CH 302 HW6 - Thompson Margaret Homework 6 Due 11:00 pm Inst...

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Thompson, Margaret – Homework 6 – Due: Oct 22 2007, 11:00 pm – Inst: James Holcombe 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points The pH of a 0.050 M H 2 CO 3 solution ( e.g. , Pepsi) is 1. between 4.0 and 4.5 2. between 3.0 and 3.5 3. more than 4.5 4. less than 3.0 5. between 3.5 and 4.0 correct Explanation: 002 (part 1 of 1) 10 points The hypothetical weak acid H 2 A ionizes as shown below. H 2 A + H 2 O * ) H 3 O + + HA - K 1 = 1 × 10 - 7 HA - + H 2 O * ) H 3 O + + A 2 - K 2 = 5 × 10 - 11 Calculate the [HA - ] in a 0.20 M solution of H 2 A. 1. 3 . 0 × 10 - 4 M 2. 1 . 0 × 10 - 7 M 3. 2 . 2 × 10 - 6 M 4. 1 . 4 × 10 - 4 M correct 5. 6 . 3 × 10 - 5 M Explanation: [H 2 ] ini = 0.20 M Let x = [HA - ]. Since we’re considering a solution of H 2 A and HA - , we should use the expression for K 1 here: K 1 = [H + ] [HA - ] [H 2 A] 1 × 10 - 7 = ( x ) ( x ) 0 . 2 - x As H 2 A has a very small K 1 , we can assume that x is very small compared to 0 . 2 and simplify our equation to 1 × 10 - 7 = ( x ) 2 (0 . 2) x 2 = 2 × 10 - 8 x = 0 . 000141421 Thus x = [HA - ] = 0 . 000141421 M. 003 (part 1 of 1) 10 points What is the pH of the solution resulting from 50.00 mL of 0.0465 M HCl mixed with 30.00 mL of 0.0197 M Ba(OH) 2 ? Correct answer: 1 . 845 . Explanation: 004 (part 1 of 1) 10 points Consider the ionization constants hypochlorous acid (HOCl) : K a = 3 . 5 × 10 - 8 ; ammonia (NH 3 ) : K b = 1 . 8 × 10 - 5 . A solution of ammonium hypochlorite (NH 4 OCl) is 1. basic, because the anion hydrolyzes to a greater extent than the cation. correct 2. neutral, because the cation and the anion hydrolyze to the same extent. 3. neutral, because the anion hydrolyzes to a greater extent than the cation. 4. acidic, because the cation hydrolyzes to a greater extent than the anion. 5. basic, because the cation and the anion hydrolyze to the same extent. 6. acidic, because the cation and the anion hydrolyze to the same extent.
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Thompson, Margaret – Homework 6 – Due: Oct 22 2007, 11:00 pm – Inst: James Holcombe 2 7. basic, because the cation hydrolyzes to a greater extent than the anion. 8. acidic, because the anion hydrolyzes to a greater extent than the cation. 9. neutral, because NH 4 OCl is a weak base/weak acid salt. 10. neutral, because the cation hydrolyzes to a greater extent than the anion. Explanation: 005 (part 1 of 1) 10 points Adding Ca(NO 3 ) 2 to pure water would result in what kind of solution? 1. basic 2. neutral correct 3. acidic Explanation: 006 (part 1 of 1) 10 points Oxalic acid is a diprotic acid with K 1 = 5 . 9 × 10 - 2 and K 2 = 6 . 4 × 10 - 5 . A dilute solution of potassium hydrogen oxalate would be 1. acidic because hydrolysis of the an- ion would predominate over further dissoci- ation. 2. basic because further dissociation of the anion would predominate over hydrolysis. 3. acidic because further dissociation of the anion would predominate over hydroly- sis. correct 4. neutral.
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