Answer :
The initial pH is slightly below 7 due to the weak acetic acid. It becomes neutral (pH 7) at the equivalence point when 25 mL of NaOH is added. Adding 50 mL or 60 mL of NaOH makes the solution basic with a pH above 7.
The pH of a solution during a titration can be calculated using stoichiometry and the Henderson-Hasselbalch equation.
At 0 mL of NaOH, the moles of acetic acid present can be determined by multiplying the volume (0.025L) by the concentration (0.1M), which yields 0.0025 moles. Since no NaOH has been added, the pH would be determined by the acid alone. The pH of the weak acetic acid can be determined using its Ka value and the formula pH = -log[H+], which would give you a pH slightly below 7.
At 25 mL of NaOH, this equates to 0.00125 moles of NaOH. Since the amounts of acetic acid and NaOH are equal, a neutralization reaction occurs, leaving no excess acid or base. Hence, the pH in this case is 7.
Adding 50 mL or 60 mL of NaOH would exceed the acetic acid concentration. To calculate the pH at this point, you would note the moles of excess base and apply -log[OH-] to find the pOH. Then subtract the pOH from 14 to get the pH. This should result in a pH above 7, showing that the solution is now basic because of the excess NaOH.
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