Question 16.18: Determine whether aqueous solutions of each of these salts a...
Determine whether aqueous solutions of each of these salts are acidic, basic, or neutral:
Analyze We are given the chemical formulas of five ionic compounds (salts) and asked whether their aqueous solutions will be acidic, basic, or neutral.
Plan We can determine whether a solution of a salt is acidic, basic, or neutral by identifying the ions in solution and by assessing how each ion will affect the pH.
Solve
(a) This solution contains barium ions and acetate ions. The cation is an ion of a heavy alkaline earth metal and will therefore not affect the pH. The anion, CH_{3}COO^{-}, is the conjugate base of the weak acid CH_{3}COOH and will hydrolyze to produce OH^{-} ions, thereby making the solution basic.
(b) In this solution, NH^{+}_{4} is the conjugate acid of a weak base (NH_{3}) and is therefore acidic. Cl^{-} is the conjugate base of a strong acid (HCl) and therefore has no influence on the pH of the solution. Because the solution contains an ion that is acidic (NH^{+}_{4}) and one that has no influence on pH (Cl^{-}), the solution of NH_{4}Cl will be acidic.
(c) Here CH_{3}NH^{+}_{3} is the conjugate acid of a weak base (CH_{3}NH_{2}, an amine) and is therefore acidic, and Br^{-} is the conjugate base of a strong acid (HBr) and therefore pH neutral. Because the solution contains one ion that is acidic and one that has no influence on pH, the solution of CH_{3}NH_{3}Br will be acidic.
(d) This solution contains the K^{+} ion, which is a cation of group 1, and the NO^{-}_{3} ion, which is the conjugate base of the strong acid HNO_{3}. Neither of the ions will react with water to any appreciable extent, making the solution neutral.
(e) This solution contains Al^{3+} and ClO^{-}_{4} ions. Cations, such as Al^{3+}, that have a charge of 3+ or higher are acidic. The ClO^{-}_{4} ion is the conjugate base of a strong acid (HClO_{4}) and therefore does not affect pH. Thus, the solution of Al(ClO_{4})_{3} will be acidic.