Answer to Question #342202 in General Chemistry for Larry

Question

1.    Calculate the pH of a buffer solution consisting of 0.50 M HC₂H₃O₂ and 0.50 M NaC₂H₃O₂ (buffer solution A). K_a of HC₂H₃O₂ = 1.75 x 10^-5.

a.     Calculate the new pH of the buffer solution after adding 0.020 mol HCl to 1.0 L of buffer solution A (5 pts).

b.    Calculate the new pH of the buffer solution after adding 0.020 mol NaOH to 1.0 L of buffer solution A (5 pts).

Answer 1

pH = pK_a + log ([salt]/[acid])

pK_a = - logK_a = 4.76

pH = 4.76 + log(0.5/0.5) = 4.76

a) pH₂ = pK_a + log ((0.5-0.02)/(0.5+0.02))= 4.76 - 0.03 = 4.73

b) pH₃ = pK_a + log(0.5+0.02)/(0.5-0.02) = 4.76 + 0.03 = 4.79