Question

(2) Given the data provided below, determine what value of pCO2 a solution of pure be in equilibrium with for the pH to be 5.0. (Ignore the difference between activity and concentration. Using the below expressions, you final answer will be in atmospheres [atm]) ater must pK= 6.35 pK2 = 10.33 AH2CO3 10-1-5PCO: Hans s Low

Answer 1

H₂CO₃ is a weak acid and it's second dissociation constant is extremely small. We can consider the H⁺ ion concentration from the first dissociation of carbonic acid only.

H₂CO₃ $\leftrightharpoons$ H⁺ + HCO₃^-. K₁

[H⁺] = √(c×K₁)

pH = 5.0

pK₁ = 6.35 ,. K₁ = 10^-6.35 = 4.4668×10^-7

[H⁺] = 10^-5.0 = 1.0×10^-5 = √(c × 4.4668×10^-7)

c × 4.4668×10^-7 = 1.0×10^-10

c = 2.2387×10^-4M = a_H2CO3

a_H2CO3 = 10^-1.5 × pCO₂

pCO₂ = 2.2387×10^-4×10^1.5 = 7.08×10^-3