A lactic acid/lactate ion buffer solution contains 0.19 M HC3H5O3 and 0.78 M C3H5O3-, respectively. The Ka value of lactic acid is 1.4*10^-4.
Calculate the pH of this buffer.
Use the Henderson-Hasselbalch equation.
To calculate the pH of a buffer solution, you need to use the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation is defined as:
pH = pKa + log([A-]/[HA])
Where:
pH = the pH of the buffer solution
pKa = the negative logarithm of the acid dissociation constant (Ka)
[A-] = the concentration of the conjugate base (in this case, C3H5O3-)
[HA] = the concentration of the acid (in this case, HC3H5O3)
In this case, the pKa value is not given directly, but it can be calculated using the Ka value. The relationship between pKa and Ka is:
pKa = -log(Ka)
Let's calculate the pKa first:
pKa = -log(1.4*10^-4)
pKa = 3.85
Now, we can substitute the given values into the Henderson-Hasselbalch equation to find the pH:
pH = 3.85 + log(0.78/0.19)
pH = 3.85 + log(4.105)
Using a calculator or a logarithm table, you can find the log(4.105) to be approximately 0.612.
pH = 3.85 + 0.612
pH ≈ 4.462
Therefore, the pH of this buffer solution is approximately 4.462.