A buffer solution is made by dissolving 0.45

moles of a weak acid (HA) and 0.13 moles of
KOH into 760 mL of solution. What is the
pH of this buffer? Ka = 3.3 × 10−6
for HA.

To find the pH of the buffer solution, we need to determine the concentration of the acidic and basic components of the buffer and then calculate the pH using the Henderson-Hasselbalch equation.

Step 1: Calculate the concentration of the acidic component (HA)
Given that we have dissolved 0.45 moles of HA in 760 mL of solution, we can calculate the concentration (C) of HA using the formula:
C = moles / volume

C(HA) = 0.45 moles / 0.760 L
C(HA) ≈ 0.592 M

Step 2: Calculate the concentration of the basic component (A-)
Since 0.13 moles of KOH are dissolved in the same volume of solution, the concentration (C) of A- can be calculated as follows:
C(A-) = 0.13 moles / 0.760 L
C(A-) ≈ 0.171 M

Step 3: Calculate the ratio of A-/HA
The Henderson-Hasselbalch equation is: pH = pKa + log(A-/HA)
But first, we need to calculate the ratio of A-/HA:
A-/HA = C(A-) / C(HA)
A-/HA ≈ 0.171 M / 0.592 M
A-/HA ≈ 0.2899

Step 4: Calculate the pKa
The pKa is the negative logarithm of the acid dissociation constant (Ka):
pKa = -log(Ka)
pKa = -log(3.3 × 10^-6)
pKa ≈ 5.48

Step 5: Calculate the pH using the Henderson-Hasselbalch equation
Now that we have the pKa value and the ratio of A-/HA, we can substitute them into the Henderson-Hasselbalch equation to find the pH:
pH = pKa + log(A-/HA)
pH ≈ 5.48 + log(0.2899)
pH ≈ 5.48 + (-0.537)
pH ≈ 4.943

Therefore, the pH of the buffer solution is approximately 4.943.

Use the HH equation.