Answer:
0.4467
Explanation:
The solution of the lactic acid and lactate acts as a buffer.
Considering the Henderson- Hasselbalch equation for the calculation of the pH of the buffer solution as:
pH=pKa+log[Conjugate base]/[acid]
Where Ka is the dissociation constant of the lactic acid.
So, pKa of the lactic acid = 3.86
pH = 3.51
So,
3.51 = 3.86 + log[Lactate]/[Lactic acid]
log[Lactate]/[Lactic acid] = -0.35
Or,
[Lactate]/[Lactic acid] = 0.4467