Chemistry/Biology 302 – Biochemistry: Exam 1 Practice Problems PLEASE NOTE: these questions come from several years of past Biochem tests. Over those years, we've used several different textbooks, and some of them use different approximate pKa values for buffers and amino acids. I've tried to update these questions so that they all use consistent pKa values, but if I've missed any inconsistencies, (a) please excuse my oversight and (b) please let me know! I do not expect you to memorize any pKa values other than those on the Amino Acid list in the syllabus. Buffers:1.)In lab, you're having fun with buffers based on a 0.1 M solution of sodium phosphate at pH 7.0. In this system, there are three pKAs: 12.7, 7.21, and 2.12. A. (10 points) You may recall that in the pre-lab lecture on the first day, you were shown a chart indicating the relative amounts of different forms of phosphate (H3PO4, H2PO4-, HPO4-2, PO4-3) needed to produce buffers of different pH. For your buffer conditions, please indicate to me the predominant phosphate species present, and the relative amounts of each at equilibrium. B. (3 points) What is the concentration of hydroxide ion in this buffer? M C. (10 points) If you were to make the same buffer using the method of question #6 in chapter three, namely, starting with 1 M phosphoric acid and adding (in our case) sodium hydroxide until the pH reached 7.0, how many moles of sodium hydroxide would it take?
D. (7 points) If you used this buffer to carry out a separation of amino acids on the Dowex (cation-exchange; that is, negatively-charged beads) chromatography column that you are using this week in lab, what order would you predict the amino acids Histidine, Lysine, Glutamine, and Alanine to elute in?