Exam2_2007crib - EXAM 2 CHEMISTRY 224 March 1, 2007 1. Read...

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EXAM 2 CHEMISTRY 224 March 1, 2007 1. Read the following instructions carefully 2. Write your name and Purdue ID number on the answer sheet 3. Write your Graduate Instructor’s name on the line for “Instructor” on the answer sheet 4. Use a #2 pencil to code all information on the answer sheet. 5. Code your name and Purdue ID number on the answer sheet 6. Code 0224 as the “Section number” on the answer sheet. 7. Code the one best answer to each question on the answer sheet. THERE ARE 20 QUESTIONS. CHECK NOW TO BE SURE THAT YOUR EXAM INCLUDES ALL 20 QUESTIONS. STATISTICAL TABLES ARE INCLUDED AT THE END OF THE EXAM. EACH QUESTION IS WORTH TEN (10) POINTS (200 POINTS TOTAL) WE STRONGLY RECOMMEND THAT YOU LOOK THROUGH THE REFERENCE MATERIALS BEFORE YOU START WORKING ON THE EXAM TO DETERMINE WHAT INFROMATION MAY COME HANDY .
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1. Illustrated below is the titration of weak diprotic acid with NaOH. Which of the following statements are true for this titration? C A B D a. At point B, the volume of the base equals the volume of the acid. b. Point A corresponds to 1:1 mole ratio of the base and the acid c. Point D corresponds to 2:1 mole ratio of the base and the acid d. Point D corresponds to 2:1 mole ratio of the acid and the base e. None of the above. Answer: c 2. For the titration illustrated in question 1, which one of the following relationships is true? a. At point A, [OH - ]=[ H 2 A] b. At point A, [H 2 A]=[HA - ] c. At point A, [OH - ]=[H 3 O + ] d. At point C, [H 2 A]=[A 2- ] e. At point C, [H 2 A]=[HA - ] Answer: b. Half of the acid molecules lost one proton.
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3. The buffer is prepared by combining 0.150 M acetic acid (CH 3 COOH) with 0.300 M sodium acetate (CH 3 COONa). Determine the pH of the buffer. a. 6.22 b. 2.37 c. 7.00 d. 4.18 e. 5.06 Answer: e. Use Henderson-Hasslebalch equation. 4. One liter of the buffer described in problem 3 is diluted with water so that the total volume increases to two liters. What happens to pH upon dilution? a. Remains approximately the same b. Goes down by 2 pH units c. Goes up by 2 pH units d. Becomes equal to pH of pure water e. Becomes equal to 3.11 Answer: a 5. The solution is prepared by combining 0.5 mM of NaOH and 0.55 mM of HCl. What is the concentration [H + ] in this solution?
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This homework help was uploaded on 04/07/2008 for the course CHEM 224 taught by Professor Scottmcluckey during the Spring '08 term at Purdue University-West Lafayette.

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Exam2_2007crib - EXAM 2 CHEMISTRY 224 March 1, 2007 1. Read...

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