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.
A lactic acid/lactate ion buffer solution contains 0.23 \it M \rm HC_3H_5O_3 and 0.65 \it M \rm C_3H_5O_3{}^-, respectively. The K_{\rm a} value of lactic acid is 1.4\times 10^{-4}. Calculate the \rm pH of this buffer.
To calculate the pH of a buffer solution, we need to use the Henderson-Hasselbalch equation, which is given by:
pH = pKa + log ([A-]/[HA])
Where:
pH = the pH of the buffer solution
pKa = the logarithmic form of Ka
[A-] = the concentration of the conjugate base (C3H5O3-)
[HA] = the concentration of the acid (HC3H5O3)
In this case, we have the following information:
[A-] = 0.78 M
[HA] = 0.19 M
Ka = 1.4 x 10^-4
Now, let's calculate the pH.
First, we need to calculate the pKa by taking the negative logarithm of Ka:
pKa = -log10(Ka)
pKa = -log10(1.4 x 10^-4)
Next, we can substitute the values into the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
pH = (-log10(1.4 x 10^-4)) + log ((0.78 M)/(0.19 M))
Now, let's calculate it:
pKa = -log10(1.4 x 10^-4) = 3.85
pH = 3.85 + log ((0.78 M)/(0.19 M))
To simplify the calculation, we can divide the concentration of [A-] by [HA]:
pH = 3.85 + log (4.11)
Finally, we can calculate the pH:
pH ≈ 3.85 + 0.613 = 4.46
Therefore, the pH of this buffer solution is approximately 4.46.