pH Vs Alkalinity

[Panneer]

Dear Everyone,

I refer to Mr.Randy holmes article on “Chemistry and the aquarium”(http://www.advancedaquarist.com/issues/may2002/chem.htm) who says that the relation of Alkalinity & pH but with CO2 concentration at 350 ppm. I would like to know the relation of pH Vs Alkalinity at 25 deg C and at equilibrium concentration of CO2 at that temperature.( I think it will be around 6 ppm). Could you suggest any other relational curve developed(for both sea water & fresh water) at this conditions.

Regards,
M.Panneer
Proposal Engineer
Chennai

 

[Chris Jury1]

You want to know the pH at 25 C with a pCO2 of 6 uatm, correct? At S = 35 and total alkalinity of 2300 at 25 C with pCO2 = 6 uatm (assuming zero conc. for silicate and phosphate) the pH will be 9.36 on the NIST scale. The easiest way to calculate such information is using the program co2sys by Ernie Lewis and Doug Wallace (what I used to give the above calculation). Google it and you'll find it. It is freely available online. Curves for determining pH, alkalinity, pCO2 and many other parameters have been developed over the years by several and have mostly been refit by Dickson and Millero. The chemistry is sufficienty complex that you'll want to use a program to make your calculations...

cj