Question

EXTREME HURRY!! State the ionization constant expression Ka for lactic acid. Given: pKa = 3.85 and Ka = 1.4*10^-4 mol dm^-3

Answer 1

Ka expression for any substance:
Ka = [H+] [A-] / [HA]

In this case,
Ka = [H+][C₃H₅O₃-]/[C₃H₆O₃]
1.4 x 10⁻⁴ = [H+] [C₃H₅O₃-] / [C₃H₆O₃]

pKa = -log(Ka)
pH = -log([H+])
The difference between pKa and pH is that pH is the negative logarithm of only the concentration of hydrogen ions, while pKa is the negative logarithm of the ratio of the product of the concentrations of hydrogen ions and concentration of base to the concentration of acid.