A lactic acid/lactate ion buffer solution contains 0.43M HC3H5O3 and 0.90M C3H5O3-. The value of lactic acid is 1.4*10-4 calculate the pH of this buffer
It's a case of plugging into the HH equation and solve. Convert Ka to pKa.
To calculate the pH of a buffer solution, you'll need to use the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
Where:
- pH is the desired pH value
- pKa is the acid dissociation constant
- [A-] is the concentration of the conjugate base (in this case, C3H5O3-)
- [HA] is the concentration of the acid (in this case, HC3H5O3)
First, let's calculate the pKa. The pKa value for lactic acid (HC3H5O3) is given as 1.4 x 10^-4. This means that pKa = -log(1.4 x 10^-4).
pKa = -log(1.4 x 10^-4) = 3.85
Now, we can substitute the given values into the Henderson-Hasselbalch equation:
pH = 3.85 + log ([C3H5O3-] / [HC3H5O3])
Given:
[C3H5O3-] = 0.90M
[HC3H5O3] = 0.43M
pH = 3.85 + log (0.90 / 0.43)
Finally, calculate the value of log (0.90 / 0.43):
log (0.90 / 0.43) ≈ 0.726
Substitute this value back into the equation:
pH ≈ 3.85 + 0.726
pH ≈ 4.576
Therefore, the pH of the lactic acid/lactate ion buffer solution is approximately 4.576.