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Re: KH pH CO2

> From: Dennis8425 at aol_com
> Subject: Re: Kh pH Co2
> Where I think a simple formula can go wrong is when there other acids
> that cause the pH shift other than CO2.  Say you have naturally acid water
> with a pH of 6.5 and dKH of 7.  If you use these to determine the CO2
> content you might be way off if most of the acidity is from HCl rather
> than CO2.

	The problems start when there are anions of weak acids in the water,
e.g., phosphate.  The relationship between CO2, HCO3- and pH applies still,
but it is no longer possible to measure either the CO2 or the HCO3-
concentrations by the usual titrations. _Strong_ acids such as HCl
or HNO3 don't cause problems, adding either reduces the KH, and the
measurement methods still work since Cl- and NO3- don't interfere
with the titrations.

Paul Sears        Ottawa, Canada