By using the Henderson Hasselbalch equation,Calculate the Pka of lactic acid when the concentration of lactic acid is 0.01 molar. the PH is 4.80 and concentration of lactate is 0.87 molar
What's the problem? This is just a plug and chug problem
pH = pKa + log(base)/(acid)
pH = 4.80
pKa = ?
base = lactate = 0.87M
acid = lactic acid = 0.01M
4.8=x +log 0.87/0.01
4.8=x +log 87
4.8=x + 1.94
4.8-1.94=x
x=2.86
pKa= 2.86
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([A-]/[HA])
where:
- pH is the solution's pH
- pKa is the acid dissociation constant of the acid
- [A-] is the concentration of the conjugate base (in this case, lactate)
- [HA] is the concentration of the acid (in this case, lactic acid)
To calculate the pKa of lactic acid, we need to rearrange the Henderson-Hasselbalch equation as follows:
pKa = pH - log([A-]/[HA])
Given:
- pH = 4.80
- [A-] (concentration of lactate) = 0.87 M
- [HA] (concentration of lactic acid) = 0.01 M
Now, substitute these values into the equation:
pKa = 4.80 - log(0.87/0.01)
To evaluate this expression, we need to calculate the logarithm first:
log(0.87/0.01) ≈ log(87)
Using a calculator, we find that log(87) is approximately 1.9395.
Now we substitute this value into the equation:
pKa = 4.80 - 1.9395
Calculating this expression gives us:
pKa ≈ 2.8605
Therefore, the pKa of lactic acid is approximately 2.8605.
To calculate the pKa of lactic acid, you can use the Henderson-Hasselbalch equation, which is:
pKa = pH + log([A-]/[HA])
Where:
pKa is the negative logarithm of the acid dissociation constant.
pH is the measure of how acidic or basic a solution is.
[A-] is the concentration of the conjugate base (lactate ion, C3H5O3-) of the acid (lactic acid, C3H6O3).
[HA] is the concentration of the acid (lactic acid, C3H6O3).
Given the values you provided:
- pH = 4.80
- [lactate] = 0.87 M
- [lactic acid] = 0.01 M
To determine the pKa, you first need to calculate the concentrations of [A-] and [HA] using the equations:
[A-] = [lactate]
[HA] = [lactic acid]
Substituting these values into the Henderson-Hasselbalch equation:
pKa = 4.80 + log(0.87/0.01)
Simplifying the expression:
pKa = 4.80 + log(87)
Using a calculator or logarithm table, you can find the value of log(87). For this particular expression, log(87) is approximately 1.9395.
Calculating the pKa:
pKa = 4.80 + 1.9395
pKa ≈ 6.74
Therefore, the pKa of lactic acid at the given concentrations is approximately 6.74.