1178564671Xuj - Anderson Kiel Homework 6 Due Mar 6 2007...

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Anderson, Kiel – Homework 6 – Due: Mar 6 2007, 5:00 pm – Inst: McCord 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. The due time is Central time. Remember Exam 2 is Thursday, 3/8 A-G in SZB 104 H-Z in WEL 2.224 001 (part 1 oF 1) 10 points A 0.28 M solution oF a weak acid is 3.5% ionized. What is the pH oF the solution? 1. 1.46 2. 5.25 3. 3.17 4. 2.01 correct 5. 0.55 Explanation: 002 (part 1 oF 1) 10 points Hydroxylamine is a weak molecular base with K b = 6 . 6 × 10 - 9 . What is the pH oF a 0.0500 M solution oF hydroxylamine? 1. pH = 9.26 correct 2. pH = 8.93 3. pH = 7.12 4. pH = 3.63 5. pH = 9.48 6. pH = 10.37 7. pH = 4.74 Explanation: Hydroxylamine is a weak base, so use the equation to calculate weak base [OH - ] con- centration (note that this is the approximate equation. Why? Because K b is very small and the concentration is reasonable) : [OH - ] = p K b C b = q (6 . 6 × 10 - 9 ) (0 . 0500) = 1 . 82 × 10 - 5 AFter fnding [OH - ], you can fnd pH using either method below: A) pOH = - log ( 1 . 82 × 10 - 5 ) = 4 . 74 pH = 14 - 4 . 74 = 9 . 26 or B) [H + ] = K w [OH - ] = 1 . 0 × 10 - 14 1 . 82 × 10 - 5 = 5 . 52 × 10 - 10 pH = - log ( 5 . 52 × 10 - 10 ) = 9 . 26 003 (part 1 oF 1) 10 points Assume that fve weak acids, identifed only by numbers (1, 2, 3, 4, and 5), have the Following ionization constants. Ionization Acid Constant K a value 1 1 . 0 × 10 - 3 2 3 . 0 × 10 - 5 3 2 . 6 × 10 - 7 4 4 . 0 × 10 - 9 5 7 . 3 × 10 - 11 The anion oF which acid is the strongest base? 1. 3 2. 5 correct 3. 4 4. 2 5. 1 Explanation: 004 (part 1 oF 1) 10 points
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Anderson, Kiel – Homework 6 – Due: Mar 6 2007, 5:00 pm – Inst: McCord 2 What is the percent ionization for a weak acid HX that is 0.40 M? K a = 4 . 0 × 10 - 7 . 1. 2.0% 2. 0.020% 3. 0.10% correct 4. 0.050% 5. 0.00020% Explanation: 005 (part 1 of 1) 10 points The term “ K a for the ammonium ion” de- scribes the equilibrium constant for which of the following reactions? 1. NH + 4 + H 2 O * ) NH 3 + H 3 O + correct 2. NH 4 Cl(solid) + H 2 O * ) NH + 4 + Cl - 3. NH 3 + H 3 O + * ) NH + 4 + H 2 O 4. The term is misleading, because the am- monium ion is not an acid. 5. NH 3 + H 2 O * ) NH 4 + + OH - 6. NH + 4 + OH - * ) NH 3 + H 2 O Explanation: 006 (part 1 of 1) 10 points Like all equilibrium constants, K w varies somewhat with temperature. Given that K w is 3 . 93 × 10 - 13 at some temperature, compute the pH of a neutral aqueous solution at that temperature. Correct answer: 6
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1178564671Xuj - Anderson Kiel Homework 6 Due Mar 6 2007...

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