Workshop CHE 168
Problem Set #7
1. Predict whether each of the following will undergo hydrolysis. If so, give the species which undergoes hydrolysis. State whether the solution is acidic, basic or neutral:
(a) KCl
(b) KF
(c) NaNO3
(d) Ca(OCl)2
(e) NH4NO2
(f) Na2HPO4
2. What is the pH of a 0.55 M aqueous solution of potassium sorbate, KC6H7O2- . [For sorbic acid: Ka = 1.7x10-5].
3. What must be the initial concentration of Al(NO3)2 (aq) for the pH at equilbrium to be 3.20?
4. It is desired to produce an aqueous solution of pH = 8.75 by dissolving in water one of the following salts: NH4Cl, KHSO4, KNO2, NaNO3. Which salt would you use and at what concentration?
5. Arrange the following 0.010 M aqueous solutions in order of increasing pH: NH3 (aq), HNO3 (aq), NaNO2 (aq), H2SO4 (aq), NaOH (aq), NH4C2H3O2 (aq), Ba(OH)2 (aq), NH4ClO4 (aq), HC2H3O2 (aq).
6. What is the pH of a 0.50 M solution of NaCN (aq). What is the percent hydrolysis in this solution?
7. The pH of an aqueous solution of NaCN is found to be 10.38. What is the [CN- ] in this solution?
8. A solution is made by adding solid sodium hypochlorite, NaOCl, to enough water to make 2.00 L of solution. If the solution has a pH of 10.50, how many moles of NaOCl were added to the water?
9. Predict whether the salt NaHCO3 will form an acidic or basic solution on dissolving in water. {Hint: write equations for the dissociation and the hydrolysis of this ion in water.}
10. Calculate the formate ion concentration and the pH of a solution that is 0.050 M in formic acid, HCHO2, and 0.100 M in HNO3.
11. What is the pH of a buffer that is 0.12 Min lactic acid, HC3H5O3, and 0.10 M in sodium lactate? [For lactic acid: Ka = 1.4x10-4]
12.
(a) How many moles of NH4Cl must be added to 2.0 L of 0.10 M NH3 (aq) to form a buffer whose pH is 9.00?
(b) Calculate the concentration of sodium benzoate that must be present in a 0.20 M solution of benzoic acid, HC7H5O2, to produce a pH of 4.00.
13. How many microliters of 1.0 M NaOH (aq) solution must be added to 50.0 mL of a 0.10 M solution of lactic acid, HC3H5O3, to produce a buffer with pH = 3.50?14. A hypothetical weak acid, HA, was combined with NaOH (aq) in the following proportions: 0.20 mol of HA, 0.080 mol of NaOH. The mixture was diluted with water to a total volume of 1.00 L and the pH measured. If the pH was found to be 4.80, what is the pKa of this weak acid?