Final answer:
To determine the pH after 4.00 mL of NaOH is added to the weak acid solution, moles of both acid and base must be calculated, then the Henderson-Hasselbalch equation is used to find the pH, which indicates a minor change due to buffering.
Step-by-step explanation:
To determine the pH at 4.00 mL of added base in the titration of a weak acid (acetic acid) with a strong base (NaOH), we will perform a series of calculations involving acid-base reactions and the equilibrium constant (Ka).
First, calculate the moles of HC2H3O3 in 23.0 mL of a 0.105 M solution:
- Moles of HC2H3O3 = 0.105 mol/L x (23.0 mL / 1000 mL/L) = 0.002415 mol
Now, calculate the moles of NaOH added at 4.00 mL of a 0.120 M solution:
- Moles of NaOH = 0.120 mol/L x (4.00 mL / 1000 mL/L) = 0.00048 mol
Next, calculate the remaining moles of acetic acid after reaction with NaOH:
- Moles of remaining HC2H3O3 = Initial moles of HC2H3O3 - Moles of NaOH = 0.002415 mol - 0.00048 mol = 0.001935 mol
Since we have a buffer solution, we use the Henderson-Hasselbalch equation to calculate the pH:
- pH = pKa + log([A-]/[HA]), where pKa = -log(Ka) and [A-] is the concentration of the acetate ion and [HA] is the concentration of acetic acid.
Using the provided information and completing these calculations will allow us to find the pH after 4.00 mL of NaOH has been added. The provided series of calculations indicates that the pH of the solution barely changes upon the addition of the base.