Calculate the pH of a 0.23 M solution of NaA (K_a for HA is 2.5 *10^-⁴) at 25°C. A) 11.88 B) 5.52 C) 8.48 D) 2.96 E) 2.12

Question

Quizplus · Accepted Answer

First, we need to determine the pKa of NaA by using the given equation: 
pKa = 14 - pKb = 14 - log(Kb)

Kb can be calculated using the Kb equation: 
Kb = Kw/Ka = 1.0 x 10^-14/2.5 x 10^-10 = 4.0 x 10^-5

pKb = -log(Kb) = -log(4.0 x 10^-5) = 4.4

pKa = 14 - 4.4 = 9.6

Now, we can use the Henderson-Hasselbalch equation to calculate the pH of the solution: 
pH = pKa + log([A-]/[HA])

[A-] can be determined from the molarity of the solution: 
[A-] = 0.23 M

[HA] can be calculated by subtracting [A-] from the initial concentration of NaA: 
[HA] = [NaA] - [A-] = 0.23 - 0.23 = 0 M

Note: [HA] is equal to zero because NaA is a salt, not an acid.

Now, we can plug in the numbers: 
pH = 9.6 + log(0.23/0) 
pH = 9.6 + infinity 
pH = 9.6

Therefore, the pH of the solution is 8.48 (Choice C).

Calculate the PH of a 0