What is the ratio of lactic acid (Ka = 1.37x10-4) to lactate in a solution with pH = 4.49?

When Ka = 1.37 x 10^-4

∴Pka = - ㏒Ka

= - ㏒ 1.37 x 10^-4

= 3.86

According to H - H equation:

when PH = PKA + ㏒[conjugate base / weak acid]

when the lactate is the conjugate base and lactic acid is the weak acid

∴ PH = Pka + ㏒[lactate] / [lactic acid]

so, by substitution:

4.49 = 3.86 + ㏒[lactate]/[lactic acid]

∴[lactate]/[lactic acid] = 4.3

∴ [lactic acid] / [lactate] = 1/4.3

= 0.23