What is the pH of a buffer that is 0.351 M HF and 0.297 M LiF? The Ka for HF is 3.5 x 10-4.
To find the pH of the buffer, we need to calculate the concentration of H+ ions in the solution.
The balanced chemical equation for the dissociation of HF is:
HF ⇌ H+ + F-
The Ka expression for HF is:
Ka = [H+][F-] / [HF]
Given that Ka = 3.5 x 10^-4, we can rearrange the equation to solve for [H+]:
[H+][F-] = Ka * [HF]
[H+] = (Ka * [HF]) / [F-]
First, we need to find the concentration of [F-]. In the buffer solution, LiF dissociates to form Li+ and F- ions. Since LiF is a strong electrolyte, it fully dissociates, and we can assume that the concentration of F- is equal to the concentration of LiF, which is 0.297 M.
Substituting the values into the equation:
[H+] = (3.5 x 10^-4 * 0.351) / 0.297
[H+] = 0.00041475
To find the pH, we can use the equation:
pH = -log[H+]
Substituting the value of [H+]:
pH = -log(0.00041475)
pH = 3.38
Therefore, the pH of the buffer is 3.38.
To determine the pH of the buffer solution, we first need to calculate the concentration of the hydronium ion (H3O+). We can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Where:
pH is the pH of the buffer
pKa is the negative logarithm of the acid dissociation constant (Ka)
[A-] is the concentration of the conjugate base
[HA] is the concentration of the acid
In this case, the acid is HF and the conjugate base is F-. The pKa value for HF is given as 3.5 x 10^-4.
1. Calculate the ratio of [A-]/[HA]:
[A-] / [HA] = (Concentration of F-) / (Concentration of HF)
[A-] / [HA] = 0.297 M LiF / 0.351 M HF
[A-] / [HA] = 0.845
2. Calculate pH using the Henderson-Hasselbalch equation:
pH = pKa + log([A-] / [HA])
pH = -log(3.5 x 10^-4) + log(0.845)
pH = -log(3.5 x 10^-4) + log(0.845)
pH = -(-3.5) + log(0.845)
pH = 3.5 + 0.075
pH ≈ 3.575
Therefore, the pH of the buffer solution is approximately 3.575.