6_new - Homework #5 holcombe (51160) This print-out should...

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Homework #5 – holcombe – (51160) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 1 10.0 points A solution of CO 2 dissolved in water is 1. neutral. 2. precipitated. 3. basic. 4. acidic. correct Explanation: 002 10.0 points What is the conjugate base of H 2 PO 4 ? 1. H 3 PO 4 2. H 2 PO 4 3. PO 3 4 4. OH 5. HPO 2 4 correct Explanation: 3 10.0 points A change in pH of 1.0 unit indicates that 1. the acid or base content decreases or in-creases by 1.0 M. 2. the volume of H + in a solution changes by an order of magnitude. 3. the acid or base content decreases or in-creases by 0.1 M. 4. the molarity of H + changes by one order of magnitude. correct 5. the salt content decreases or increases by 1.0 M. Explanation: If the pH of a solution is 1.0, that means that the H + concentration is 0.1 M. If the pH is 2.0, the H + concentration is 0.01 M. The di f erence is one order of magnitude. 004 10.0 points What would be the pH of a solution of hypo- bromous acid (HOBr) prepared by dissolving 9.7 grams of the acid in 20 mL of pure wa- ter (H 2 O)? The Ka of hypobromous acid is 2 × 10 −9 1. 4 correct 2. 10 3. 6 4. 13 5. 1 Explanation: 9.7 g HOBr × 1 mol = 0.1 mol HOBr 97 g 0.1 mol HOBr = 5 M HOBr 0.02 L H 2 O [H + ] = (K a · C a ) 1 / 2 = (2 × 10 −9 · 5) 1 / 2 = (10 −8 ) 1 / 2 = 10 −4 pH = − log[H + ] = − log(10 −4 ) = 4 005 10.0 points How much acetic acid (K a = 1.8 × 10 −5 ) must be used to prepare a liter of solution having a pH of 2.75? 1. 5.69 moles 2. 0.435 moles 3. 0.0101 moles 4. 0.178 moles correct 5. 9.88 moles Explanation:
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Homework #5 – holcombe – (51160) 2 + −pOH pH = − log[H + ] = 2.75 [C 3 H 7 NH 3 ] = [OH ] = 10 = 10 −2 . 14 = 0.00724436 mol/L so The K b is + −1 −3 [H ] = log (−2.75) = 1.778 × 10 mol K b = [C 3 H 7 NH 3 + ][OH ] [C 3 H 7 NH 2 ] + 2 (0.00724436) HA H + A = Substitute [H + ] = [A ] = 1.778 × 10 −3 0.1 − 0.00724436
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This note was uploaded on 04/04/2012 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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6_new - Homework #5 holcombe (51160) This print-out should...

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