Reflecting on the Calculation of Weak Acid HA's pKa
How can we calculate the pKa of the weak acid HA based on the given information?
Given that a solution contains 1.15 in HA and 0.852 in A- with a pH of 5.06, what is the pKa of the weak acid HA?
Calculating the pKa of Weak Acid HA
The pKa of the weak acid HA is approximately 5.19. To calculate the pKa, we can utilize the Henderson-Hasselbalch equation:
The Henderson-Hasselbalch equation is given by:
pH = pKa + log ([A-] / [HA])
Given the values of pH, [A-], and [HA] from the problem, we can substitute them into the equation:
5.06 = pKa + log(0.852 / 1.15)
Following the steps:
- Calculate the value inside the logarithm: 0.852 / 1.15 ≈ 0.7409
- Substitute back into the equation: 5.06 = pKa + log(0.7409)
- Isolate pKa: pKa = 5.06 - log(0.7409)
- Calculate log(0.7409) ≈ -0.13
- Substitute back into the equation: pKa ≈ 5.06 - (-0.13)
- Finally, calculate pKa: pKa ≈ 5.19