As of right now, I just need help with part A. I can\'t figure out where to star

Question

As of right now, I just need help with part A. I can't figure out where to start. I was trying to use henrys law but that isnt really working either.

Please show all work!

Thanks

A septic tank leaks water into an adjacent groundwater aquifer, adding high amounts of dissolved organic carbon to the aquifer. As the dissolved organic carbon (DOC) oxidizes (i.e. CH2O + O2 (g) CO: (g) + H2O). carbon dioxide (CO2) is added to the groundwater system. After the oxidation of the dissolved organic carbon, the partial pressure of carbon dioxide in the aquifer is Pco 10-2.5 atm. Assume that the system does not exchange mass with the atmosphere (i.e., the aquifer is a "closed system"). Assuming that the temperature of the groundwater is 15 degreeC. calculate the pH of the groundwater. Given what you know about the pH sensitivity of speciation within the carbonate system, PREDICT which carbonate species are the two that will be relevant at this p11. Explain your rationale to receive full credit Calculate the relative activity ratios of these two spccics at the pH you calculated in (a). Assume you are a hydrologist and/or environmental consultant whose job it is to ascertain if the septic tank is leaking. Your clients want this done cheaply and quickly, since such a leak is time-sensitive. What approach do you propose to the clients? Explain your approach. Assume there are abundant wells in this area, since the locals use well water and the aquifer is well studied and sampled, but you may also place wells wherever you want. Use the map view diagram below (on which you should mark your sampling locations) to help explain your approach in (d):

Explanation / Answer

Using Henery law you will be able to calculate concentration of CO2 in the water

CO2 + H2O ----> H2CO3 (carbonic acid)

[CO2] = [H2CO3]

H2CO3 is a weak acid with Ka 4.5 * 10^-7 . This obtained from online search. This is pKa1 of carbonic acid

so [H+] = [H2CO3] * Square root (Ka) = [CO2] * squareroot (4.5 * 10^-7)

pH = -log [H+] = - log { [CO2] * squareroot (4.5 * 10^-7) }

In above equation just plug the [CO2] obtained from henery's law

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