Question

A chemistry student wants to see the effect of adding a specific buffer on the equilibrium position of a 0.1 M acetic acid (CH3COOH) and 0.1 M sodium acetate (CH3COONa) solution. If the initial pH of the solution is 4.7, what is the pH of the solution after adding the buffer? (Ka of acetic acid is 1.8 x 10^-5).

Answer 1

To determine the pH of the solution after adding the buffer, we can use the Henderson-Hasselbalch equation:pH = pKa + log  [A-]/[HA] where pH is the solution's pH, pKa is the negative logarithm of the acid dissociation constant  Ka , [A-] is the concentration of the conjugate base  acetate ion, CH3COO- , and [HA] is the concentration of the weak acid  acetic acid, CH3COOH .First, we need to find the pKa of acetic acid:pKa = -log Ka  = -log 1.8 x 10^-5   4.74Since the initial pH of the solution is 4.7, which is very close to the pKa value, we can assume that the solution is already acting as a buffer. Therefore, adding more buffer to the solution will not significantly change the pH, as the buffer's purpose is to resist changes in pH.In conclusion, the pH of the solution after adding the buffer will still be approximately 4.7.