A buffer solution was prepared by mixing 442 mL of 0.181 M NaOCl and 139 mL of 0.421 M HOCl. Calculate the pH of the solution given that Ka (HOCl) is 3.2 x 10-8.
See your first post. Same song, second verse. You must go through and determine the concns of the acid and base.
To calculate the pH of the buffer solution, we need to determine the concentration of the acidic and basic components of the buffer solution, as well as the dissociation constant (Ka) of the acidic component (HOCl).
The acidic component of the buffer is HOCl, which is a weak acid. The basic component is the salt NaOCl, which is the conjugate base of HOCl. In a buffer solution, the acid and its conjugate base must be present in roughly equal amounts. Therefore, to calculate the concentration of HOCl and NaOCl in the buffer solution, we will use the concept of molarity (M) and the volume of the solutions given.
Step 1: Calculate the moles of HOCl and NaOCl:
Moles of HOCl = concentration (M) × volume (L)
Moles of HOCl = 0.421 M × 0.139 L = 0.058519 moles
Moles of NaOCl = concentration (M) × volume (L)
Moles of NaOCl = 0.181 M × 0.442 L = 0.080162 moles
Step 2: Determine the ratio of moles (acid:base):
Since HOCl and NaOCl have a 1:1 stoichiometric ratio, the moles are approximately equal.
Step 3: Calculate the total volume of the buffer solution:
Total volume = volume of HOCl solution + volume of NaOCl solution
Total volume = 0.139 L + 0.442 L = 0.581 L
Step 4: Calculate the concentration of HOCl and NaOCl in the buffer solution:
Concentration (M) = moles / total volume
Concentration of HOCl = 0.058519 moles / 0.581 L = 0.1007 M
Concentration of NaOCl = 0.080162 moles / 0.581 L = 0.1380 M
Step 5: Calculate the pH of the buffer solution:
pH = pKa + log(base/acid)
Given that the Ka (HOCl) is 3.2 × 10^(-8), we can calculate the pKa as follows:
pKa = -log(Ka)
pKa = -log(3.2 × 10^(-8))
pKa = -(-7.5) = 7.5 (approximately)
Now, substitute the values into the pH equation:
pH = 7.5 + log(0.1380/0.1007)
pH = 7.5 + log(1.369)
pH = 7.5 + 0.137
pH ≈ 7.637 (approximately)
Therefore, the pH of the buffer solution is approximately 7.637.