Calculate the ph of a buffer that is 0.13m in lactic acid and 0.10m in sodium lactate.

According to Henderson-Hasselbalch Equation,

pH = pKa + log [Lactate] / [Lactic Acid]

As,

Ka of Lactic Acid = 1.38 * 10⁻⁴

pKa = - log Ka

pKa = - log 1.38 * 10⁻⁴

pKa = 3.86

So,

pH = 3.86 + log [0.10] / [0.13]

pH = 4.74 + log 0.769

pH = 4.74 - 0.11

pH = 4.63