hw 8 ch 302 - obennoskey(blo242 Homework#8 Holcombe(52460...

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obennoskey (blo242) – Homework #8 – Holcombe – (52460) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points Which oF the Following is NOT true For a solution bu±ered at a selected pH? 1. The solution pH will increase a lesser amount than a non-bu±ered solution, when base is added. 2. The bu±ered solution contains an acid and its conjugate base. 3. The bu±ered solution could be made to be either acidic or basic. 4. The solution pH will not change with the addition oF an acid. correct Explanation: Bu±ers are solutions which contain compar- ative amounts oF a conjugate weak acid/base part and allow For only small changes in the pH oF a chemical system, compared to non- bu±ered solutions, when an acid or a base is introduced. 002 10.0 points What is the pH oF a solution containing 0.3 M NH 4 Cl and 0.6 M NH 3 ? The p K a oF the ammonium ion is 9.25. 1. 9.55 correct 2. 4.45 3. 12.25 4. 8.95 5. 5.05 Explanation: ²or NH + 4 , p K a = 9.25 p K b = p K w - p K a = 14 - 9 . 25 = 4 . 75 p K b = - log K b K b = 10 - p K b = 10 - 4 . 75 = 1 . 77828 × 10 - 5 Building an ICE using molarities, NH 3 (aq)+H 2 O( ) NH + 4 (aq)+OH - (aq) 0.6 - x + x + x 0 . 6 - x 0 . 3 + x + x K b = [NH + 4 ] [OH - ] [NH 3 ] = (0 . 3 + x ) x 0 . 6 - x 0 . 3 x 0 . 6 x = 0 . 6 K b 0 . 3 = 0 . 6 (1 . 77828 × 10 - 5 ) 0 . 3 = 3 . 55656 × 10 - 5 = [OH - ] [H + ] = K w [OH - ] = 1 × 10 - 14 3 . 55656 × 10 - 5 = 2 . 81171 × 10 - 10 Thus pH = - log(2 . 81171 × 10 - 10 ) = 9 . 55103 003 10.0 points What is the pH oF an aqueous solution that is 0.10 M HCOOH ( K a = 1 . 8 × 10 - 4 ) and 0.10 M NaHCO 2 ? 1. 5.74 2. 10.26 3. 3.74 correct 4. 2.38 5. 5.62 Explanation: 004 10.0 points
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obennoskey (blo242) – Homework #8 – Holcombe – (52460) 2 Which of the following combinations CAN- NOT produce a buFer solution? All compo- nents are present in 0.10 M concentration.
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This note was uploaded on 04/14/2010 for the course CH CH302 taught by Professor Mccord during the Spring '10 term at University of Texas at Dallas, Richardson.

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hw 8 ch 302 - obennoskey(blo242 Homework#8 Holcombe(52460...

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