Calculate the concentration of all species in a 0.180 M solution of H2CO3.
[H2CO3], [HCO−3], [CO2−3], [H3O+], [OH−]
Enter your answers numerically separated by commas. Express your answer using two significant figures.
The Best Answer for Calculate the concentration of all species in a 0.180 M solution of H2CO3?
Tricky. That’s because there are NO molecules of H2CO3 in a solution of carbonic acid. Molecules of H2CO3 do not exist in liquid water. Carbonic acid is actually a solution of CO2 in equilibrium with small amounts of H+ ions and HCO3^- ions. The equilibrium lies far to the left, which means that most of the CO2 stays CO2.
CO2(aq) + H2O(l) <==> H+ + HCO3^-
HCO3^- is a weak acid, so there will be even less CO3^2- in solution.
HCO3^- <==> H+ + CO3^2-
CO2(aq) + H2O(l) <==> H+ + HCO3^- ……….. Ka = 4.3×10^-7 (*)
Ka = [H+][HCO3^-] / [CO2]
4.3×10^-7 = x² / 0.180
x = 2.8×10^-4 …. x = [H+] = [HCO3^-]
[H+] = 2.8×10^-4 …… pH = 3.57
[OH-] = 1.0×10^-14 / 2.8×10^-4 = 3.6×10^-11
HCO3^- <==> H+ + CO3^2- …… Ka = 4.8×10^-11
Ka = [H+][CO3^2-] / [HCO3^-]
4.8×10^-11 = [CO3^2-]