Using the information provided below including the equations of chemical equilib

Question

Using the information provided below including the equations of chemical equilibrium given,
determine the pH of pure water in equilibrium with the atmosphere.
Henry's Law of Equilibrium [H2CO3*] = Kh*PCO2
where:
[H2CO3*] = the concentration (moles/liter) of dissolved carbonic acid in the water
Kh = Henry's Constant for CO2 (29.76 moles/liter*atm)
PCO2 = Partial Pressure of CO2 in the atmosphere (3.5x10-4 atm)

Disassociation of Water
[H2O] ? [H+] + [OH-] pKa = 14 therefore [H+][OH-]
[H2O] = 10^-14
Disassociation of Carbonic Acid
[H2CO3*] ? [H+] +[ HCO3-] pKa = 6.3 therefore [H+][ HCO3-][H2CO3*] = 10^-6.3
[ HCO3-] ? [H+] +[CO3-2] pKa = 10.3 therefore [H+][CO3-2][ HCO3-]= 10^-10.3
Equation of Electroneutrality
(sum of moles of negative charges must equal the sum of moles of positive charges)

[H+] = [OH-] + [ HCO3-] + 2*[CO3-2]

Explanation / Answer

First, we calculate the amount of CO2 dissolved in water under an atmosphere of pressure from Henry

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