a) s -1 b) 0.10 s -1 c) s -1 d) 0.50 s -1 e) 0.50 M -1 s -1 ** Google Sheets Used to plot and calculate

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2 1. The reactant concentration in a first-order reaction was 1.70 M after 35.0 sec and 0.01 M after 85.0 sec. What is the rate constant for this reaction? a) s -1 b) 0.10 s -1 c) s -1 d) 0.50 s -1 e) 0.50 M -1 s -1 ** Google Sheets Used to plot and calculate 2. Which of the following molecules is NOT known to act as an enzyme? a) Metallic groups b) Proteins c) RNA d) DNA e) none of the above 3. The decarboxylation of a β-keto acid catalyzed by a decarboxylation enzyme can be measured by the rate of CO2 formation. From the initial rates given in the table below, what is the maximum velocity of CO2 formation? a) 0.10 µmol / min b) 0.20 µmol / min c) 0.30 µmol / min d) 0.40 µmol / min e) 0.50 µmol / min ** Google Sheets Used to plot and calculate Page 2

3 4. Ascorbic acid (Vitamin C) is a mono-anion at neutral ph. It is a powerful antioxidant, which scavenges free radicals. It is oxidized in a single-electron oxidation to the mono-hydroascorbate radical anion (MDHA - ) according to the reaction: Asc - MDHA - + H + + e - The half-reaction has a standard reduction potential of V. Ascorbate also undergoes a twoelectron oxidation to dehydroascorbate (DHA): Asc - DHA + H + + 2e - This half-reaction has a standard reduction potential of V. Finally, MDHA - undergoes a disproportionation reaction: 2 MDHA + H + DHA + Asc - Determine the biochemical standard free-energy change (ΔG o' ) for this reaction. a) kj mol -1 b) kj mol -1 c) kj mol -1 d) kj mol -1 e) kj mol V -2* *( ) Page 3

4 5. Consider the following reaction, in which two electrons are transferred from cytochrome-c (reducted): 2 Cyt-c[Fe 2+ ] + pyruvate + 2H + 2 Cyt-c[Fe 3+ ] + lactate Calculate the standard Gibbs free-energy change at ph 7 and 25 o C if the lactate concentration is 5 times the pyruvate concentration, and the cytochrome-c (Fe 3+ ) concentration is 100 times the cytochrome-c (Fe 2+ ) concentration.. a) 48.9 kj mol -1 b) 84.5 kj mol -1 c) 99.9 kj mol -1 d) kj mol -1 e) kj mol The conversion of β- hydroxybutyrate (β-hb - ) to acetoacetate (AA - ) is an important biochemical redox reaction that uses molecular oxygen as the ultimate oxidizing agent: β-hb - + ½ O2 (g) AA - + H2O Calculate the equilibrium constant for this system at ph 7 and 25 o C. a) 1.8 x b) 1.1 x c) 90.4 d) 2.2 x e) -2.2 x Page 4

5 7. In acidic conditions, benzyl penicillin (BP) undergoes the following parallel reaction: In the molecular structures, R1 and R2 indicate alkyl substituents. In a solution where ph=4, the rate constants for the processes at 22 o C are k1 = s -1, k2 = s -1, k3 = s -1. (A) What are the percent yields for P1, P2, and P3 formation? (6 pts) ** Google Sheets Used to calculate Page 5

6 (B) The temperature dependence of the acid-catalyzed hydrolysis of penicillin is investigated, and the dependence of k1 on temperature is given in the following table: Temperature ( o C) k1 (s -1 ) What is the activation energy (Ea) and Arrhenius pre-exponential factor (A) for this branch (P1) of the hydrolysis reaction? (9 pts) [Put a box around your final answers. Express your answer for Ea in units of kj/mol and your answer for A in units of s -1 ] ** Google Sheets Used to plot and calculate Page 6

7 8. The decomposition of N2O5 is an important process in tropospheric chemistry. The half-life for the first-order decomposition of this compound is sec. How long will it take for a sample of N2O5 to decay to 75% of its initial value? [Put a box around your final answers. Express your answer in units of seconds (s)] sec Page 7

8 9. Consider the following sequential reaction scheme: (A) Plot the concentration profiles ([A], [I] and [P] versus time) for the above sequential reaction where the rate constant for A I is 0.4 inverse seconds and eight times the rate of I P (i.e., ka = 8kI = 0.4 s -1 ). (10 pts) (B) Determine the time at which [I] is at a maximum for the above sequential reaction, i.e., ka = 8kI = 0.4 s -1. [Express your answer in units of seconds. Put a box around your final answer] (5 pts) ** Google Sheets Used to plot and calculate (Screen shot shown above) Page 8

9 10. Proflavine has been used as a bacterial disinfectant and topical antiseptic. However, its use has been limited because it is also a mutagenic compound arising from its ability to intercalate between nucleic-acid base pairs in DNA. Although the monomeric form of proflavin can intercalate, the dimer cannot. The monomer and dimer forms of proflavine exist in equilibrium in solution: and it has been determined under certain room temperature conditions that the dimerization rate constant (k1) was M -1 s -1 and the rate constant for dissociation of the dimer back to monomers (k-1) was s -1. In addition, the apparent rate constant for the relaxation of this system toward equilibrium is equal to: If 10.0 millimolar (mm) of monomer is present at equilibrium, (A) what is the equilibrium constant for the dimerization reaction (5 pts), and (B) the concentration of dimer present at equilibrium (5 pts)? [Express your answer for (A) in units of M -1, and for (B) in units of molarity (M). Put boxes around your final answers] The differential rate expression for the monomer is At equilibrium, the change in [M] as a function of time is zero, so, (A) (B) [M2] = dimer concentration = 0.01 M * 0.01 M * /M = 3.5x10-3 M (3.5 mm) Page 9

10 (C) how long does it take for equilibrium to be achieved (5 pts)? [Express your answer in units of seconds (inverse the apparent rate constant). Put box around your final answer] Kapp = k k1 [M]eq = s ( M -1 s -1 )(0.01 M) = 4.8x10 6 s -1 The inverse of kapp is the time constant for the relaxation toward equilibrium, or 2.1x10-7 sec (0.21 microseconds) for this example. The relaxation can be considered complete after five-time constants, or approximately 1 microseconds. Page 10

11 11. Calculate the midpoint potential for a protein that was measured to have the following redox data. The parameter R is the ratio of the reduced form divided by the total amount of protein. Use table 6.1 in J. Allen s Biophysical Chemistry textbook to guess which protein this is. [Put box around your final answer] Potential (mv) R Bchl + + e - Û Bchl is the closest at 640 mv Page 11

12 12. The concentrations of the principal ions in a sample of intracellular fluid are 60.0 mm for potassium hydrogen phosphate, 80.0 mm for sodium chloride, 20.0 mm for magnesium chloride, and 10.0 mm for calcium sulfate. Calculate the ionic strength of the intracellular fluid. [Put a box around your final answers. Express your answer in units of mm.] I = 0.36 M = 360 mm To break it down by compound: K2HPO4 (0.06 M), which is 0.12M K + and 0.06 M HPO4 2-, so, NaCl (0.08 M), which is 0.08M Na + and 0.08 M Cl -, so, MgCl2 (0.02 M), which is 0.02M Mg 2+ and 0.04 M Cl -, so, CaSO4 (0.01 M), which is 0.01 M Ca 2+ and 0.01 M SO4 2-, so, ** Advanced consideration, co-solubility of all these salts in aqueous solution. Page 12