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ps3a - R-NH3 fl R-NH2 H(a In what pH range can glycine...

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MCB 100 - Problem Set 3. August 29, 2003 Q1. What is a hydronium ion? (A) a hydrated proton (B) is a hydrated hydrogen ion (C) has the structure H3O+ (D) is the usual form of one of the dissociation products of water in solution (E) All of the above is true Q2. The pH of blood is 7.4. The pH of gastric juice is 1.4. What is the ratio of the concentration of H+ (or H3O+) in blood to that in gastric juice? Q3. The strongly polar properties of water make it an excellent solvent for charged molecules, whereas nonionized and nonpolar organic molecules are poorly soluble in water. Are the following compounds more soluble in an aqueous solution of 0.1 M NaOH or 0.1 M HCl? Q4. The amino acid glycine if often used as the main ingredient of a buffer in biochemical experiments. The amino group of glycine, which has a pKa of 9.6, can exist either in the protonated form (-NH3+) or as the free base (-NH2) because of the reversible equilibrium:
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Unformatted text preview: R-NH3+ fl‡ R-NH2 + H+ (a) In what pH range can glycine be used as an effective buffer due to its amino group? (b) In a 0.1 M solution of glycine at pH 9.0, what fraction of glycine has its amino group in the -NH3+ form? (c) How much 5 M KOH must be added to 1.0 L of 0.1 M glycine at pH 9.0 to bring its pH to exactly 10.0? (d) When 99% of the glycine is in its -NH3+ form, what is the numerical relation between the pH of the solution and the pKa of the amino group? Q5. A compound has a pKa of 7.4. To 100 mL of a 1.0 M solution of this compound at pH 8.0 is added 30 mL of a 1.0 M solution of hydrochloric acid. The resulting solution is at what pH? (A) 7.58 (B) 7.40 (C) 7.22 (D) 6.8 (E) 6.53 Q7. When compared to Watson-Crick hydrogen bonding, the shapes of correctly paired nucleotide bases are as important, if not more, in determining the fidelity of DNA replication. Explain why this is so....
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