-over- Chem 101B: Problem Set 2 Zumdahl, Chapter 8 (Acid-base Problems) Due: Monday, September 12, 2011 There will be other Ch. 8 problems on solubility equilibria. They will appear on the next problem set. Problems from the textbook: It is crucial that you do these, but you do not have to hand them in for grading. They give you extremely helpful practice for mastering buffers and titration curves. You’ll find it much easier to do the problems that must be handed in if you do these first! 6th edition: 16, 19, 21, 37, 41, 46, 53, 57, 59, 64, 67, 68, 75acegi, 79, 115 5th edition: 17, 19, 21, 33, 37, 43, 45, 49, 51, 56, 57, 59, 67acegi, 69, 99 Problems to hand in for grading: (these are not easy—work on the book problems to get practice and master concepts before trying these) 1. Given 15.75 mL of 0.230 M formic acid, HCOOH: a. How many milliliters of 0.450 M potassium formate, KCO2H, must be added to produce a buffer with pH 3.95? b. How many milliliters of 0.450 M KOH must be added to produce a buffer with pH 3.95? 2. For titration of 30.0 mL of 0.500 M HCN with 0.500 M NaOH: a. Which indicator or indicators would be effective in detecting the endpoint? Why? b. For each effective indicator you listed in your answer to part a, state the color of the titration solution before and after the endpoint. c. Draw an accurate titration curve, including the volumes and pH values for the equivalence point and halfway point 3. Draw a titration curve for each of the following situations. Include the volumes and pH values for all equivalence points and halfway points. a. 45.0 mL of 0.250 M KOH is titrated with 0.400 M HCl b. 15.0 mL of 0.150 M CH3NH2 is titrated with 0.200 M HCl c. 20.0 mL of 0.100 M 1,2-propanediamine, CH3CH(NH2)CH2NH2, a compound that accepts protons at two different N atoms, is titrated with 0.100 M HCl. The pKb values for 1,2-propanediamine are 4.18 and 7.39.PS 2, page 2 4. Find the pH of the following solutions generated from the materials in the bottles shown below: Bottle A 200.0 mL of 0.0750 M HCl Bottle B 200.0 mL of 0.200 M hydrazine (H2N-NH2, pKb = 5.88) Bottle C 100.0 g of solid hydrazine hydrochloride, H2N-NH3Cl a. Solution #1: 6.80 g of the solid in Bottle C dissolved in water to give a total volume of 500.0 mL b. Solution #2: Mix 75.0 mL of Solution #1 with 75.0 mL of the solution in Bottle B. c. Solution #3: Mix 15.0 mL of the solution in Bottle A with 50.0 mL of Solution #2. 5. Consider the diprotic acid H2A, with pKa1 = 2.75 and pKa2 = 6.25. H2A is colorless, HA– is blue, and A2– is yellow. a. When a 50.0 mL sample of 0.0950 M H2A is titrated with 0.0950 M NaOH, the following curve is obtained. For all of the equivalence and halfway points, label the axes and write in the corresponding pH values and volumes. b. What color is the solution when the pH is 9.25? Explain. c. At what pH will the solution appear most blue? Explain. d. At what pH will the solution appear green?