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pH calculation


rawls423
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Hi,

 

I have the following information and am wondering if it is possible to calculate the pH. I do not know anything more specific about the alkalinity. All concentrations are mg/L. The sample is open to the atmosphere

 

Ba ++ 383
Ca ++ 2438
Fe ++ 5.904
K+ 109.1
Li+ 24.9
Mg++ 238
Mn++ 1.672
Na+ 11786.4
SiO2 (aq) 42.55
Sr++ 431.2
Cl- 23100.0
SO4-- 35.5
Br- 263
NO3- 17.9
Carbonate Alkalinity 292 mg/L as CaCO3

 

Thank you!

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Hi,

 

The GWB programs require you to set pH explicitly when using the alkalinity to constrain the total carbonate component concentration. Typically when you measure alkalinity you should measure the initial pH as well. Autotitrators that record pH as acid is added are really nice for this.

 

If you had this information, you would use SpecE8 to add each of the above species to the Basis pane and set their values with mg/l units. For HCO3-, you would set the concentration to 292 with units mg/l_as_CaCO3. For H+, you would choose pH units.

 

Since you know the fluid is open to the atmosphere, you might guess the pH and run the equilibrium model to determine the CO2 fugacity. Use trial and error to find a pH that yields a log CO2 fugacity of -3.5.

 

Hope this helps,

 

Brian Farrell

Geochemist

Aqueous Solutions LLC

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