Problem Set
GENERAL BIOCHEMISTRY
Problem Set No. 1
Answered by: Andrea Rose A. Fajardo of BSFT 2-1N
1. Calculate the pH of a dilute solution that contains a molar ratio of potassium acetate to acetic acid (pKa=4.76) of: a. 2:1 pH = 4.76 + log[2]/[1] = 4.76 + 0.3010 = 5.06 b. 1:4 pH = 4.76 + log[1]/[4] = 4.76 + (-0.6021) = 4.16 c. 6:5 pH = 4.76 + log[6]/[5] = 4.76 + 0.0792 = 4.81 d. 2:3 pH = 4.76 + log[2]/[3] = 4.76 + (-0.1761) = 4.58 e. 9:1 pH = 4.76 + log[9]/[1] = 4.76 + 0.9542 = 5.71 2. A buffer contains 0.01mol of lactic acid (pKa=3.86) and 0.05mol of sodium lactate per liter. a. What is the resulting pH of the buffer? pH = 3.86 + log[0.05]/[0.01] = 3.86 + 0.6990 = 4.56 b. Calculate the change in pH when 5mL of 0.5M HCl is added to 1L of buffer. 5mL of 0.5 mol/L 5mL * 1L/1000mL = 0.005L 0.005L * 0.5 mol/L = 0.0025mol NaC3H5O3 = 0.05mol - 0.0025mol = 0.0475 C3H5O3 = 0.01mol - 0.0025mol =0.0075 pH = 3.86 + log[0.0475]/[0.0075] = 3.86 + 0.8016 = 4.66 • 4.55-4.66 = 0.11 is the change in pH c. What pH change would you expect if you added the same quantity of HCl to 1L of pure water? [H+] = (0.0025mol)(1L) = 0.0025M pH = -log 0.0025 = 2.60 3. The structure of the amino acid of isoleucine is given at the right. a. How many chiral centers does it have? 2 b. How many optic isomers? 4 c. Draw the perspective formulas for all the optical isomers of isoleucine.
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4. A peptide has the sequence: Glu-His-Trp-Ser-Leu-Arg-Pro-Gly a. What is the charge of the molecules at pH 4 and 11? (Use pKa values of those in the ppt)
|pH
Problem Set No. 1
Answered by: Andrea Rose A. Fajardo of BSFT 2-1N
1. Calculate the pH of a dilute solution that contains a molar ratio of potassium acetate to acetic acid (pKa=4.76) of: a. 2:1 pH = 4.76 + log[2]/[1] = 4.76 + 0.3010 = 5.06 b. 1:4 pH = 4.76 + log[1]/[4] = 4.76 + (-0.6021) = 4.16 c. 6:5 pH = 4.76 + log[6]/[5] = 4.76 + 0.0792 = 4.81 d. 2:3 pH = 4.76 + log[2]/[3] = 4.76 + (-0.1761) = 4.58 e. 9:1 pH = 4.76 + log[9]/[1] = 4.76 + 0.9542 = 5.71 2. A buffer contains 0.01mol of lactic acid (pKa=3.86) and 0.05mol of sodium lactate per liter. a. What is the resulting pH of the buffer? pH = 3.86 + log[0.05]/[0.01] = 3.86 + 0.6990 = 4.56 b. Calculate the change in pH when 5mL of 0.5M HCl is added to 1L of buffer. 5mL of 0.5 mol/L 5mL * 1L/1000mL = 0.005L 0.005L * 0.5 mol/L = 0.0025mol NaC3H5O3 = 0.05mol - 0.0025mol = 0.0475 C3H5O3 = 0.01mol - 0.0025mol =0.0075 pH = 3.86 + log[0.0475]/[0.0075] = 3.86 + 0.8016 = 4.66 • 4.55-4.66 = 0.11 is the change in pH c. What pH change would you expect if you added the same quantity of HCl to 1L of pure water? [H+] = (0.0025mol)(1L) = 0.0025M pH = -log 0.0025 = 2.60 3. The structure of the amino acid of isoleucine is given at the right. a. How many chiral centers does it have? 2 b. How many optic isomers? 4 c. Draw the perspective formulas for all the optical isomers of isoleucine.
[pic]
4. A peptide has the sequence: Glu-His-Trp-Ser-Leu-Arg-Pro-Gly a. What is the charge of the molecules at pH 4 and 11? (Use pKa values of those in the ppt)
|pH