Consider the visually plotted titration curve for of Acetic Acid () titrated against . The curve sho — Ionic Equilibrium Chemistry Question
Question
Consider the visually plotted titration curve for $100 \text{ mL}$ of $0.1 \text{ M }$ Acetic Acid ($pK_a = 4.74$) titrated against $0.1 \text{ M } NaOH$. The curve shows a gentle buffer region before spiking upwards. Using theoretical interpolation, what is the exact pH value on the visual y-axis exactly when $50 \text{ mL}$ of the $NaOH$ solution has been added to the flask?
💡 Solution & Explanation
The initial volume of the weak acid is $100 \text{ mL}$. Because the molarities of both the acid and the titrant ($NaOH$) are perfectly identical ($0.1 \text{ M}$), the equivalence point strictly requires exactly $100 \text{ mL}$ of $NaOH$. Adding $50 \text{ mL}$ of $NaOH$ corresponds precisely to the exact half-equivalence point. Visually, this is the center of the buffer plateau on the graph. At exact half-neutralization, $[Salt] = [Acid]$, so by the Henderson-Hasselbalch equation, $pH = pK_a$. Therefore, the pH is identically 4.74.