19. What is the pH of a solution made from equal volumes of 0.20-molar propionic acid and 0.20-molar sodium propionate?

20. A solution is 0.10 molar in formic acid and 0.010 molar in sodium formate. What is the pH of the solution?

21. If 0.010 mole of HCl gas is dissolved in one liter of pure water, what is the final pH? If the same amount of HCl is dissolved instead in one liter of the buffer solution of Problem 19, what is the final pH?

22. If 20 mI of a solution of 0.6-molar ammonia are mixed with 10 ml of a 1.8-molar ammonium chloride solution, what is the final pH? If 1 mI of a 1.0 molar HCl solution is added, what will the pH become? If the buffer solution had been prepared from 0.06-molar ammonia and 0.18-molar ammonium chloride, would the same HCl solution change the pH more, or less, than in the first situation? Why?

23. Novocain (Nvc) is a weak organic base that reacts with water as follows:

Nvc + H₂O = NvcH⁺ + OH^-

The base-equilibrium constant for this reaction is K_b = 9.0 x 10^-6. Suppose that a 0.010-molar solution of Novocain is titrated with nitric acid. (a) What is the pH of the Novocain solution at the beginning of titration, before any acid has been added?

(b) At the end point of the titration, the solution behaves just like a solution of 0.010-molar NvcH⁺NO₃^-. What is the pH of this solution? (c) The indicator bromcresol green has a pK_a of 5.0. Is this indicator suitable for the titration?

24. The solubility of silver phosphate, Ag₃PO₄, in water is 0.0065 g liter^-1 at 20'C. What is the solubility product (K_sp) for this salt? What is the solubility of silver phosphate in moles liter^-1 in a solution that contains a total of 0.10 mole liter^-1 of Ag⁺?

25. If a solution containing 0.16 mole liter^-1 of Pb²⁺ is made 0.10 molar in chloride ion, 99.0% of the Pb²⁺ is removed as PbCl₂. What is K_sp for PbCl₂?

Data in the table on Page 34 will help you solve the following problems.

26. Calculate the solubility in moles liter^-1 of MgF₂ in pure water. What is the solubility in 0.050-molar NaF?

27. What is the solubility of CoS in pure water in moles liter^-1? What is the solubility of CoS in 0.10-molar sodium sulfide solution?

28. What is the silver ion concentration in a solution of silver chromate in pure water? In 0.10-molar chromate solution?