Question

1) Which combination is the best choice to use when preparing a buffer with a pH of 5.5?
A) HNO₂; NaNO₂ (pK_a for HNO₂ = 3.33)

B) HCHO₂; NaCHO₂ (pK_a for HCHO₂ = 3.74)

C) C₅H₅N; C₅H₅NHCl (pK_b for C₅H₅N = 8.76)

D) NH₃; NH₄Cl (pK_b for NH₃ = 4.75)

2) A 100 mL solution of 0.500 M hydrocyanic acid is titrated with a 0.125 M solution of potassium hydroxide. What is the pH of the solution after the addition of 500 mL of the potassium hydroxide solution?  
- For hydrocyanic acid: K_a = 4.9 x 10^-10 and pKa = 9.31
- report answer in three significant figures

Answer 1