HW 6 Solutions

# HW 6 Solutions - Wright Jacqueline – Homework 6 – Due...

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Unformatted text preview: Wright, Jacqueline – 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 3.5 and 4.0 correct 3. between 3.0 and 3.5 4. less than 3.0 5. more than 4.5 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 . × 10- 4 M 2. 6 . 3 × 10- 5 M 3. 1 . 4 × 10- 4 M correct 4. 2 . 2 × 10- 6 M 5. 1 . × 10- 7 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 ) . 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. acidic, because the anion hydrolyzes to a greater extent than the cation. 2. neutral, because the cation hydrolyzes to a greater extent than the anion. 3. neutral, because the anion hydrolyzes to a greater extent than the cation. 4. neutral, because the cation and the anion hydrolyze to the same extent. 5. acidic, because the cation hydrolyzes to a greater extent than the anion. 6. basic, because the anion hydrolyzes to a greater extent than the cation. correct Wright, Jacqueline – Homework 6 – Due: Oct 22 2007, 11:00 pm – Inst: James Holcombe 2 7. basic, because the cation and the anion hydrolyze to the same extent. 8. neutral, because NH 4 OCl is a weak base/weak acid salt. 9. basic, because the cation hydrolyzes to a greater extent than the anion. 10. acidic, because the cation and the anion hydrolyze to the same extent. 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. acidic 3. neutral correct 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. neutral....
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## This note was uploaded on 12/08/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

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HW 6 Solutions - Wright Jacqueline – Homework 6 – Due...

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