Question

Answer the following three questions: a) What is the pH of an aqueous solution with a hydrogen ion concentration of [H ] = 4.2 × 10–9 M?

b) What is the hydroxide ion concentration, [OH–], in an aqueous solution with a hydrogen ion concentration of [H ] = 4.2 × 10–9 M?

c) A monoprotic acid, HA, dissociates:

The equilibrium concentrations of the reactants and products are [HA] = 0.130 M [H ] = 3.00 × 10–4 M [A–] = 3.00 × 10–4 M Calculate the Ka value for the acid HA.

Answer 1

a). [H+] = 4.2 times 10^- 9M pH = -log (14 + 1) pH = -log (4.2 times 10 ^- 9) pH = -(- 8.38) pH = 8.38 b). [H+] [0H] = 10 ^- 14 [- oH] = 10 - 14/[H] [H+] = 4.2 times 10 ^- 9 M [- oH] = 10 ^- 14/4.2 times 10 ^- 9 [oH] = 2.38 times 10^- 6M [oH] = 2.38 times 10^- 6M c). HA equilibrium H^+ + A ^- K_a = [product]/[reactant] K_a = [H+] [A-]/[HA] [H+] = 3.00 times 10 ^-4 M [A-] = 3.00 times 10 ^- 4 M [HA] = 0.130 M K_a = (3.00 times 10 ^- 4M) (3.00 times 10 ^- 4 M)/(0.130M) => K_a = 6.92 times 10^- 7M \r\n < null >