Chemistry HW 7 - ekk86 hw07 Holcombe (53570) This print-out...

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ekk86 – hw07 – Holcombe – (53570) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points When sodium Formate is added to HCOOH(aq), 1. the pH oF the solution increases. correct 2. the pH oF the solution decreases. 3. the pH oF the solution does not change. 4. the K a increases. 5. the equilibrium concentration oF HCOOH(aq) decreases. Explanation: 002 10.0 points Some solid NH 4 Cl is added to a water solution oF NH 3 . Which oF the Following statements is correct? 1. [H 3 O + ] oF the solution remains the same. 2. [OH - ] oF the solution increases. 3. The pH oF the solution increases. 4. The pH oF the solution decreases. cor- rect Explanation: The salt NH 4 Cl dissociates in solution, giv- ing the spectator ion Cl - and NH + 4 which hydrolyzes to NH 3 and H 3 O + . This decreases the pH. 003 10.0 points Which oF the Following mixtures can produce a bu±er? 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 bu±er 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. 004 10.0 points Which oF the Following is NOT true For a solution bu±ered at a selected pH? 1. The bu±ered solution contains an acid and its conjugate base. 2. The bu±ered solution could be made to be either acidic or basic. 3. The solution pH will increase a lesser amount than a non-bu±ered solution, when base is added. 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. 005 10.0 points Which oF the Following would cause the pH oF a 0.10 M solution oF H² to decrease? 1. adding solid Na² 2. adding some Ag + which would precipitate part oF the ² - From the solution as solid Ag² correct
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ekk86 – hw07 – Holcombe – (53570) 2 3. adding solid KNO 3 4. dissolving gaseous NH 3 in the solution 5. adding more water Explanation: M HF = 0.10 M HF + H 2 O ± ² H 3 O + +F - HF is a weak acid. Adding NaF would create a bufer by supplying the conjugate base F - , consuming H 3 O + and making the solution less acidic (higher pH). Similarly, the base NH 3 would react with H 3 O + and pH would increase. Adding more water would dilute the solution, reducing the concentration. Solid KNO 3 , the salt o± a strong acid and a strong base, would have no efect on pH. AgF is an insoluble salt and would precipitate out i± Ag + ions are added and in turn equilibrium would shi±t to the right, producing more H 3 O + and lowering the pH.
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This note was uploaded on 11/01/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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Chemistry HW 7 - ekk86 hw07 Holcombe (53570) This print-out...

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