Consider a solution of 2.0 M HCN and 1.0 M NaCN (K_a for HCN = 6.2 × 10^-10). Which of the following statements is true? A) The solution is not a buffer because [HCN] is not equal to [CN^-]. B) [OH^-] [H⁺] C) The pH will be below 7.00 because the concentration of the acid is greater than that of the base. D) The buffer will be more resistant to pH changes from addition of strong acid than to pH changes from addition of strong base. E) All of these statements are false.

Question

Consider a solution of 2.0 M HCN and 1.0 M NaCN (K_a for HCN = 6.2 × 10^-10). Which of the following statements is true? A) The solution is not a buffer because [HCN] is not equal to [CN^-]. B) [OH^-] > [H⁺] C) The pH will be below 7.00 because the concentration of the acid is greater than that of the base. D) The buffer will be more resistant to pH changes from addition of strong acid than to pH changes from addition of strong base. E) All of these statements are false.

Quizplus · Accepted Answer

The solution is a buffer because it contains a weak acid (HCN) and its conjugate base (CN⁻). In a buffer solution, [OH⁻] > [H⁺] when the base concentration is significant, which is the case here.

Consider a Solution of 2