Question

Calculate the pH and concentrations of the following species in a 0.025M carbonic acid solution. (Given Ka1=4.3x10^-7 and Ka2=5.6x10^-11

a) H2CO3 b)HCO3- c)CO32- d)H+ e)OH-

Answer 1

Answer: Here the first thing is to be noted that the concentration of H+ ion is second dissociation is neglected as it is a very low value , Means H+ concentration is majorly depends upon the first dissociation

  H2CO3 ↔ H+ + HCO3-

here , [H+] = [HCO3^-]

Ka1 = 4.3 * 10^-7 = [H+] ² / [H2CO3] = [H+] ² / 0.025

[H+]²  = 1.075 * 10^-8

H+ = 1.0368 * 10^-4 M

Hence the concentration of [H+] = [HCO3^-] = 1.0368 * 10^-4 M

And Ph = - log [ 1.0368 * 10^-4 ]   

Ph = 3.98

Hence POH = 14-3.98 = 10.02

[OH-] = 9.5499 * 10^-11 M

Hence , It is all about the given question . Thank you :)