What is the pH of a solution that consists of 0.50 M H₂C₆H₆O₆ (ascorbic acid) and 0.75 M NaHC₆H₆O₆ (sodium ascorbate)? For ascorbic acid, K_a = 6.8 *10¯⁵ A) 3.76 B) 3.99 C) 4.34 D) 4.57 E) 5.66

Question

Quizplus · Accepted Answer

To solve this problem, we need to use the equation for the acid dissociation constant (Ka) of ascorbic acid:

Ka = [H+][C6H8O6-]/[C6H8O6]

We can assume that the concentration of [C6H8O6] is equal to the total concentration of ascorbic acid (0.50 M), since ascorbic acid is a weak acid and only partially dissociates in water.

We can also assume that the concentration of [C6H8O6-] is equal to the concentration of sodium ascorbate ([Na+][C6H7O6-]), since sodium ascorbate is a strong base and completely dissociates in water. The concentration of [Na+] can be assumed to be equal to the concentration of sodium ascorbate (0.75 M).

Therefore, we can write:

Ka = [H+][C6H8O6-]/[C6H8O6]
6.8 x 10^-1 = [H+][C6H7O6-]/0.50

We can solve for [H+]:

[H+] = Ka x [C6H8O6]/[C6H7O6-]
[H+] = (6.8 x 10^-1) x (0.50)/0.75
[H+] = 0.453 M

To calculate the pH, we take the negative log of [H+]:

pH = -log[H+]
pH = -log(0.453)
pH = 4.34

Therefore, the pH of the solution is 4.34, which is closest to choice C.

What Is the PH of a Solution That Consists of 0.50