CH302 Spring 2009 Practice Quiz 3—The TA Version 1. Which of the following pairs of solutions would result in a buffer upon mixing? 1. 25 mL of 4 M HCl & 15 mL of 4 M HNO2 2. 200 mL of 0.5 M LiOH & 100 mL of 0.5 M H2SO4 3. 100 mL of 1 M NH3 & 10 mL of 10 M HNO3 4. 150 mL of 3 M Ba(OH)2 & 200 mL of 2 M HClO 5. 100 mL of 1 M CH3COOH & 50 mL of 1 M NaOH 2. What would be the pH of a solution prepared from 2 L of H2O, 85 g of NH3 and 98 g of NH4Br? Assume the Kb of ammonia is 2x10-5. 1. 4 2. 5.4 3. 10 4. 8.6 5. 7 3. Two liters of a buffer containing 0.6 M CH3NH2 and 0.8 M CH3NH3Cl has 102.4 g of HI added to it. What is the new pH? Assume the Kb of CH3NH3 is 6x10-4. 1. 6 2. 3 3. 11 4. 4 5. 10 6. 8 4. A 0.08 M CH3NH2 solution is titrated against a 0.08 M HCl solution. Assuming the Kb of CH3NH2 is 4x10-10, what is the pH at the equivalence point? 1. 3 2. 7 3. 9 4. 5 5. not enough information 5. Consider the molecule ethylenediaminetetraacetic acid (EDTA): As drawn above, how many Ka would be needed to describe the complete deprotonation of EDTA? 1. 4 2. 6 3. 3 4. 5 6. What would be the difference in pH of a 1 M solution of NaH2AsO4 and a 1 M solution of Na2HAsO4? Assume H3AsO4 has a pKa1 of 2 and a pKa2 of 7 and a pKa3 of 12.1. 7 2. 4.5 3. 9.5 4. 5 5. 2.5 6. 1.5 7. A student erroneously calculated that a solution consisting solely of a weak base dissolved in water had a pH of 6. Which two of the following might have been true? I. Kb < 10-11 II. Kb > 10-3 III. Cb > 10-1 IV. Cb < 10-4 1. I and IV only 2. II and III only 3. I and III only 4. II and IV only 8. An aqueous system with Na2CO3, NaCl and NH4Cl dissolved in it would require how many equations to find all the unknown equilibrium concentrations? 1. 3 2. 7 3. 4 4. 6 5.
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