L1 /
9
CH3041
pH [CO2]
CALCULATION
(2) CO2 + H2O D HCO3- + H+ pKa1 = 6.35
Taking an
atmospheric [CO2] of
350 ppm
calculate the pH of a raindrop at sea level,
KH CO2 = 3.38 x 10-2 mol L-1 atm-1.
%i = ppmvi x 10-4 pi = (%i / 100) patm [i(aq)] = pi KH
calculate the pH of a raindrop at sea level,
KH CO2 = 3.38 x 10-2 mol L-1 atm-1.
%i = ppmvi x 10-4 pi = (%i / 100) patm [i(aq)] = pi KH
Ka1 = 10-pKa1 = 10-6.35 = 4.45 x 10-7
pCO2 = {(350 x 10-4)/100} x 1atm = 3.50 x 10-4 atm
pCO2 = {(350 x 10-4)/100} x 1atm = 3.50 x 10-4 atm
[CO2] = KHpCO2 = 3.38x10-2 mol L-1atm-1 x 3.50x10-4 atm
= 1.183 x 10-5 mol l-1
Ka1 = [H+][HCO3-]/[CO2] in (2) [H+] = [HCO3-].
Þ [H+]2 /[CO2] = 4.45 x 10-7
= 1.183 x 10-5 mol l-1
Ka1 = [H+][HCO3-]/[CO2] in (2) [H+] = [HCO3-].
Þ [H+]2 /[CO2] = 4.45 x 10-7
Þ [H+]2 = [CO2] x 4.45
x 10-7
Þ [H+] = (1.183 x 10-5 x 4.45 x 10-7)½
= 2.29 x 10-6 mol L-1
pH = - log10[H+] = 5.64 rather than pH = 7
