Question

a) why is the bicarbonate solution basic based on Ka and Kb values? b) why is the carbonate solution more basic than the bicarbonate solution based on Ka or Kb values?

Answer 1

a) Bicarbonate solution is weakly basic in nature. for example sodium bicarbonate in the solution gives,

NaHCO₃ + H₂O H₂CO₃ + OH^- + Na⁺

Kb value for this reaction is 4x10³.

As K_b is quite high i.e tendency of bicarbonate to get proton is more than to loose one

Hence bicarbonate solution is basic in nature.

b) In case of carbonate solution i.e

Na₂CO₃ + H₂O NaHCO₃ + Na⁺ + OH^-

the value of K_b is found to be 2.13x10¹⁰. which is quite high as compared to that of the bicarbonate. Hence carbonate soultion is more basic than the bicarbonate solution. Moreover carbonate is conjugate base of weak acid i.e carbonic acid, so it is a strong base.