Question

What is the ratio of lactic acid (Ka = 1.37x^10-4) to lactate in a solution with pH =4.29

Answer 1

Henderson–Hasselbalch equation is given as,

                                         pH  =  pKa  +  log [A⁻] / [HA]   -------- (1)

Solution:

Convert Ka into pKa,

                                         pKa  =  -log Ka

                                         pKa  =  -log 1.37 × 10⁻⁴

                                         pKa  =  3.863

Putting value of pKa and pH in eq.1,

                                         4.29  =  3.863 + log [lactate] / [lactic acid]

Or,

                   log [lactate] / [lactic acid]  =  4.29 - 3.863

                   log [lactate] / [lactic acid]  =  0.427

Taking Anti log,

                             [lactate] / [lactic acid]  =  2.673

Result:

           2.673 M  lactate salt when mixed with 1 M Lactic acid produces a buffer of pH = 4.29.