Quiz 1, BICH 410 (TuTh 12:45-2), Tuesday, Sept. 17, 1996
Clearly circle the letter corresponding to your answer for each problem. There are seven problems, six of which count 3 points, and one is worth 2 points. No partial credit given for multiple-choice questions.
(Your quiz may have been a different version, with questions and possible answers mixed differently. However the content of the two versions is identical.)
1. The pH of a solution is 4.0. What is the concentration of hydroxide ion in the same solution?
- A) 10-4 M
- B) 10 millimolar
- C) 10-10 M
- D) 10-3 M
- E) none of the above
Answer: C; pH + pOH = 14, so pOH = 10; then [OH-] = 10-10 M
2. The reaction shown below is an example of what type of biochemical reaction?
(glycerol kinase reaction - top of Fig. 16-4)
- A) group transfer
- B) condensation
- C) rearrangement
- D) oxidation-reduction
- E) cleavage
3. Predict which of the following solutions would have the lowest pH.
- A) 0.1 M NaOH
- B) 1 M lactic acid (pKa = 3.86)
- C) 1 M acetic acid (pKa = 4.76)
- D) 1 M formic acid (pKa = 3.75)
- E) 0.1 M acetic acid (pKa = 4.76)
Answer: D; lowest pKa means highest equilibrium constant for dissociation
4. Which of the following functional groups canNOT be involved in hydrogen bonds?
- A) imidazole
- B) hydroxyl
- C) amido
- D) phenyl
- E) carbonyl
Answer: D; phenyl group has no hydrogens attached to electronegative atoms, nor an electronegative hydrogen bond acceptor atom, such as found in other choices.
5) Which of the following factors contribute to the force of the ionic interaction between a carboxylate group (pKa approx. 4) and an amino group (pKa approx. 10) in solution:
- A) the dielectric constant of the solvent
- B) the distance between the charged groups
- C) the pH of the solution
- D) all of the above
- E) factors A) and B) only
Answer: D; dielectric constant involved in charge shielding by the solvent; pH affects amount of charge on these groups; force of interaction varies inversely with square of distance between charges
6) The pKas for the ionization of H2CO3 are 3.8 and 10.2. Which of the following statements is true for a solution of these species at pH 5.8?
- A) There is twice as much H2CO3 compared to HCO3-1, and a negligible amount of CO3-2.
- B) There is 100 times as much H2CO3 compared to HCO3-1, and a negligible amount of CO3-2.
- C) There is twice as much HCO3-1 compared to H2CO3, and a negligible amount of CO3-2.
- D) There is 100 times as much HCO3-1 compared to H2CO3, and a negligible amount of CO3-2.
- E) There is 100 times as much HCO3-1 compared to CO3-2, and a negligible amount of H2CO3.
Answer: D; pH of 5.8 is 2 units above pKa of 3.8 - therefore 2 orders of magnitude, or 100 times more of conjugate base, HCO3- compared to acid, H2CO3; pKa for next ionization is over 4 units higher, so a negligible amount of CO3-2 is present.
7) (2 pts) Which of the following would contribute toward a reaction being exergonic?
- A) a decrease in the entropy
- B) an increase in the enthalpy
- C) an increase in the entropy
- D) an endothermic reaction
- E) none of the above
Answer: C; exergonic means G < 0 which is "caused by" either enthalpy decrease (exothermic) or entropy increase