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# solution7_pdf - toupal(rgt374 Homework 7 Sutclie(52410 This...

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toupal (rgt374) – Homework 7 – Sutcliffe – (52410) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. NOTE: a p in front of a K a or K b value means to get the actual value of K a or K b , you must use the 10 x button on your calculator, in the same way you find [H + ] from pH. SEC- OND NOTE: Hydrolyse means ’react with water’ 001 10.0 points A solution of 0.2 M boric acid is prepared as an eye wash. What is the approximate pH of this solution? For boric acid K a = 7 . 2 × 10 - 10 . 1. pH = 6 2. pH = 5 correct 3. pH = 3 4. pH = 7 5. pH = 4 Explanation: 002 10.0 points The pH of 0 . 015 M HNO 2 (nitrous acid) aque- ous solution was measured to be 2 . 63. What is the value of p K a of nitrous acid? 1. 3.59 2. 0.97 3. 4.24 4. 3.36 correct 5. 2.90 6. 2.63 Explanation: M = 0 . 015 M pH = 2 . 63 Analyzing the reaction with molarities, HNO 2 + H 2 O H 3 O + + NO - 2 0 . 015 - 0 0 - x - x x 0 . 015 - x - x x [H 3 O + ] = [NO - 2 ] = 10 - pH = 10 - 2 . 63 = 0 . 00234423 mol / L . The K a is K a = [H 3 O + ][NO - 2 ] [HNO 2 ] = (0 . 00234423) 2 0 . 015 - 0 . 00234423 = 0 . 000434222 and the p K a is p K a = - log(0 . 000434222) = 3 . 36229 . 003 10.0 points A 7 . 2 × 10 - 3 M solution of acetic acid is 5.0% dissociated. In a 7 . 2 × 10 - 4 M solution, the percent dissociation would be 1. the same. 2. zero. 3. < 5%. 4. None of these 5. > 5%. correct Explanation: 004 10.0 points The amide ion NH - 2 can react with water to form ammonia (NH 3 ) and a hydroxide ion. Which is true about this reaction? 1. NH 3 is the conjugate acid of NH - 2 . cor- rect 2. Water and ammonia are a conjugate acid- base pair. 3. The hydroxide ion is the conjugate base of the amide ion.

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toupal (rgt374) – Homework 7 – Sutcliffe – (52410) 2 4. Water and the amide ion are a conjugate acid-base pair. 5. The amide ion is acting as an acid. Explanation: 005 10.0 points What is the pH of a 0 . 006 M KOH solution? 1. 2.22 2. 7.00 3. 5.12 4. 11.78 correct 5. 8.88 Explanation: [KOH] = 0 . 006 M KOH is a strong base which completely dissociates in aqueous solution: KOH -→ OH - + K + [OH - ] = [KOH] = 0 . 006 M [H 3 O + ] = K w [OH - ] = 1 × 10 - 14 0 . 006 M = 1 . 66667 × 10 - 12 M pH = - log[H 3 O + ] = 11 . 7782 006 10.0 points
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