We’re being asked to calculate the pH of the NaHCO3 solution.
NaHCO3 will break up in the solution:
NaHCO3- → Na+ + HCO3-
HCO3- is the conjugate base of carbonic acid. Carbonic acid is a diprotic acid, it can donate two protons (H+) and it will have two equilibrium reactions.
Ka1 = 4.3x10-7
• 1st equilibrium reaction: H2CO3(aq) + H2O(l) → HCO3-(aq) + H3O+(aq)
Ka2 = 5.6x10-11
• 2nd equilibrium reaction: HCO3-(aq) + H2O(l) → CO32-(aq) + H3O+(aq)
An amphoteric salt is one that contains an anion that can act as either an acid or a base in water. Baking soda, NaHCO3, is an example. By combining the ionization and hydrolysis reactions of the anion, we get the principle reaction that occurs when this salt is dissolved in water.
2 HCO3- → CO32- + H2CO3
The pH for such a solution is (pka1+pka2)/2
Calculate the pH of the NaHCO3 solution.
Frequently Asked Questions
What scientific concept do you need to know in order to solve this problem?
Our tutors have indicated that to solve this problem you will need to apply the Diprotic Acid concept. You can view video lessons to learn Diprotic Acid. Or if you need more Diprotic Acid practice, you can also practice Diprotic Acid practice problems.