CHEM 302 HW8 - jrr944 – Homework 8 – Lyon – (53565) 1...

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Unformatted text preview: jrr944 – Homework 8 – Lyon – (53565) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This homework assignment is due Monday, March 24, by 11PM. 001 10.0 points Which of the following mixtures can produce a buffer? I) NH 3 + NaOH II) NH 3 + NH 4 Cl III) H + + OH- IV) HClO 2 + NaClO 2 V) (CH 3 ) 3 NHCl + (CH 3 ) 3 N 1. II only 2. II, III, and IV only 3. I, III, and V only 4. IV only 5. II, IV, and V only correct Explanation: A buffer contains a weak acid or weak base, plus the salt of that weak acid or base; or, a mixture which will have this composition after any acid-base reactions occur. 002 10.0 points Buffers are useful because 1. they change the pH of a system signifi- cantly. 2. they are only active inside the human body. 3. they have extremely high melting points. 4. they can consume a relatively large amount of acid or base without a significant change in pH. correct Explanation: A buffer solution is one that resists changes in pH when strong acids or strong bases are added. It contains an acid and its conjugate base, so it can react with added bases or acid. 003 10.0 points A buffer is composed of NH 3 and NH 4 Cl. How would this buffer solution control the pH of a solution when a small amount of a strong base is added? 1. The OH- reacts with the NH + 4 . correct 2. The OH- reacts with the Cl- . 3. The OH- reacts with the NH 3 . 4. The OH- reacts with the H 2 O. Explanation: Cl- is a spectator ion and does not react. The NH 3 is the base, B, and NH + 4 is the conjugate acid BH + . So when base is added, it will react with the acid. 004 10.0 points A buffer solution containing acetic acid and sodium acetate is resistant to large change in pH when a strong base is added because 1. some of the acetic acid ionizes to produce hydronium ions, which partly neutralize the added hydroxide ions. correct 2. some of the acetate ion hydrolyzes pro- ducing hydronium ions, which partly neutral- ize the added base. 3. the stated effect would not occur; this solution is buffered only against the addition of a strong acid. 4. some of the added hydroxide ions react with hydronium ions from the acid and more acetic acid is then formed from the acetate ions present. 5. the acetate ion reacts with part of the hydroxide ions so that the effect on the pH is small. jrr944 – Homework 8 – Lyon – (53565) 2 Explanation: In the buffer system, CH 3 COOH is in equi- librium with its conjugate base CH 3 COO- : CH 3 COOH + H 2 O ⇀ ↽ CH 3 COO- + H 3 O + , so that the pH remains relatively stable. OH- from the added base reacts with...
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