Chem2 hw6s - Yoon, Seong Meen – Homework 6 – Due: Oct...

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Yoon, Seong Meen – 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 – fnd 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 3.0 and 3.5 2. between 3.5 and 4.0 correct 3. between 4.0 and 4.5 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. 1 . 0 × 10 - 7 M 2. 6 . 3 × 10 - 5 M 3. 2 . 2 × 10 - 6 M 4. 3 . 0 × 10 - 4 M 5. 1 . 4 × 10 - 4 M correct 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. acidic, because the cation hydrolyzes to a greater extent than the anion. 2. basic, because the cation hydrolyzes to a greater extent than the anion. 3. neutral, because NH 4 OCl is a weak base/weak acid salt. 4. basic, because the cation and the anion hydrolyze to the same extent. 5. acidic, because the anion hydrolyzes to a greater extent than the cation. 6. neutral, because the cation hydrolyzes to a greater extent than the anion.
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Yoon, Seong Meen – Homework 6 – Due: Oct 22 2007, 11:00 pm – Inst: James Holcombe 2 7. neutral, because the cation and the anion hydrolyze to the same extent. 8. acidic, because the cation and the anion hydrolyze to the same extent. 9. neutral, because the anion hydrolyzes to a greater extent than the cation. 10. basic, because the anion hydrolyzes to a greater extent than the cation. correct 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. basic because hydrolysis of the anion would predominate over further dissocia- tion. 2.
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Chem2 hw6s - Yoon, Seong Meen – Homework 6 – Due: Oct...

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