Question

1. What are the two pKa values for carbonic acid? What is the pH of a 0.100M solution of sodium bicarbonate? What is the pH of a 0.100M solution of sodium carbonate?

Answer 1

Ans 1- The pka values of carbonic acid are 6.35 for carbonic (I) and 10.33 for carbonic (II). Carbonic (I) has the molecular formula of H2CO3 while carbonic (II) has the molecular formula of HCO3-.This is when it is at 25 degree C means at room temprature.

the ka value is 4.68 x 10^-11 for Sodium carbonate

[H⁺] = Ka . C_{weak acid or base}

C = .1 M

[H+] = 4.68 x 10^-11 . x.1

[H+] = 2.16x10^-6

pH = - log[H+]

pH = 5.66

Kb for sodium bicarbonate is = 1.736x10⁸

[OH-] =Kb . C

Kw=Ka.Kb

Ka =5.76x10^-23

[H+] Ka . C

[H+] = 2.4x10^-12

pH = -log H⁺

pH = 11.619