16.52 The pH of a sodium acetate/acetic acid buffer is 4.50. Calculate the ratio [CH3COO-]/[CH3COOH].
16.53 The pH of blood plasma is 7.40. Assuming the principal buffer sysem is HCO3-/H2CO3, calculate the ratio [HCO3-]/[H2CO3]. Is this buffer moe effective against an added acid or an added base?
16.60 A student wishes to prepare a buffer solution at pH = 8.60. Which of the following weak aids should she choose and why? HA (Ka = 2.7 x 10-3), HB (Ka = 4.4 x 10-6), or HC (Ka = 2.6 x 10-9).
16.63 A 5.00-g quantity of a diprotic acid is dissolved in water and made up to exactly 250 mL. Calculate the molar mass of the acid if 25.0 mL of this solution required 11.1 mL of 1.00 M KOH for neutralization. Assume that both protons of the acid are titrated.
16.64 Calculate the pH at the equivalence point for the following titrations: (a) 0.10 M HCl versus 0.10 M NH3, (b) 0.10 M CH3COOH versus 0.10 M NaOH.
16.65 A sample of 0.1276 G of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.0633 M NaOH solution. The volume of base required to reach the equivalence point was 18.4 mL. (a) Calculate the molar mass of the acid. (b) After 10.0 mL of base had been added in the titration, the pH was determined to be 5.87. What is the Ka of the unknown acid?
16.67 Sketch titration curves for the following acid-base titrations: (a) HCl versus NaOH, (b) HCl versus NH3, (c) CH3COOH versus NaOH. In each case, the acid is added to the base in an Erlenmeyer flask. Your graphs should show pH as the y-axis and volume of acid added as the x-axis.
16.71 A student carried out an acid-base titration by adding NaOH solution from a buret to an Erlenmeyer flask containing HCl solution and using phenolphthalein as indicator. At the equivalence point, she observed a faint reddish-pink color. However, after a few minutes, the solution gradually turned colorless. What do you suppose happened?
16.80 Cacodylic acid is (CH3)2AsO2H. Its ionization constant is 6.4 x 10-7. (a) Calculate the pH of 50.0 mL of a 0.10 M solution of the acid. (b) Calculate the pH of 25.0 mL of 0.15 M (CH3)2AsO2Na. (c) Mix the solutions in part (a) and part (b). Calculate the pH of the resulting solution.
16.83 A volume of 25.0 mL of 0.100 M HCl is titrated against a 0.100 M NH3 solution added to it from a buret. Calculate the pH values of the solution (a) after 10.0 mL of NH3 solution have been added, (b) after 25.0 mL of NH3 solution have been added, (c) after 35.0 mL of NH3 solution have been added.
16.87 What is the equilibrium constant for the following reaction:
CH3COOH(aq) + OH-(aq)
CH3COO-(aq) + H2O(l)