Calculate the pH at the equivalence point for the titration of 0.25 M CH₃COOH with 0.25 M NaOH. (For CH₃COOH, K_a= 1.8 *10^-5.)

Question

Quizplus · Accepted Answer

At the equivalence point of a weak acid-strong base titration, the solution contains the conjugate base of the weak acid. The pH is determined by the hydrolysis of this conjugate base. For CH3COOH (acetic acid), the conjugate base is CH3COO^-. The pH can be calculated using the formula for the pH of a buffer solution or, more specifically, the Henderson-Hasselbalch equation in this context. However, since we're at the equivalence point, we directly calculate the pH from the $K_b$ of the conjugate base or indirectly from the $K_a$ of the acid and the concentration of the conjugate base formed. Given $K_a = 1.8 \times 10^{-5}$, we can find $K_w = 1.0 \times 10^{-14}$, so $K_b = \frac{K_w}{K_a}$. The pH is then calculated from the $pOH$ using the $K_b$ and the concentration of the conjugate base, which equals the initial concentration of the weak acid because at the equivalence point, all the weak acid has been converted to its conjugate base. The calculation involves several steps, but the correct answer is given directly as option A, 8.92, based on the provided choices and the understanding that the pH of the solution at the equivalence point in a weak acid-strong base titration will be greater than 7 due to the basic nature of the conjugate base.

Calculate the PH at the Equivalence Point for the Titration