Determine the equilibrium pH for a 1.0 mM solution of NaHCO3 that is in equilibrium with a CO2(g) partial pressure of 0.10 atm. What is the pH after this solution comes to equilibrium with the atmosphere (assume H2CO3* = 10-5.0). Please solve by spread sheet.
HCO3- (aq) + H2O (l) <----------> H2O (l) + CO2 (g) + OH- (aq)
For this reaction, Kb = Kw / Ka = 1.0*10-14 / 10-5 = 10-9
Thus from the given data -
Kb = [OH-] PCO2 / [HCO3-]
10-9 = [OH-] (0.10) / 0.001
[OH-] = 10-11 M
Thus - [H+] = 10-14 / 10-11 = 0.001 M
pH = -log [H+] = 3
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