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Human blood is a natural buffer which has an average carbon dioxide concentration of around 0.0022 mol dm-3. This is in equilibrium with a hydrogencarbonate ion concentration of around 0.024 mol dm-3. The Ka for the following equilibrium is 4.5 × 10-7 mol dm-3:
|
H2O(l) + CO2(aq) |
What is the pH of human blood?
[HA] = [CO2] = 0.0022 mol dm-3 (this is the proton donor)
[A-] = [HCO3-] = 0.024 mol dm-3 (this is the proton acceptor)
pKa = - log10Ka = - log10(4.5 × 10-7) = 6.35
Put this data into the equation:
pH = 6.35 - log10(0.0022/0.024) = 7.4
HCO3