At 298 K , the pK_a of hydrocyanic acid ( HCN ) is 9.30 and the pK_b of ammonia ( NH ₃ ) is 4.74 . The pH of an aqueous solution of ammonium cyanide at this temperature will be:

Step-by-step solution

Ammonium cyanide ( NH ₄ CN ) is a salt of a weak acid ( HCN ) and a weak base ( NH ₃ ). The pH of an aqueous solution of a salt of a weak acid and a weak base is given by the formula: pH = 7 + 1 2 (pK_a - pK_b) Substituting the given values: pH = 7 + 1 2 (9.30 - 4.74) pH = 7 + 1 2 (4.56) pH = 7 + 2.28 = 9.28 Answer: 9.28