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Re: Stoichiometry Anyone?
Todd H. wrote:
> If my understanding of the definition of KH is correct, then this
> formula seems to have an incorrect conversion of KH to moles HCO3-.
> Is it correct that:
>
> 1 GH = 1 KH = 10 mg/L CaO = .3566 meq/L = .3566 mmoles/L HCO3-?
>
> For the result to indicate dissolved CO2 in mg/L, shouldn't the
> constant
> be:
>
> .3566 * 44.01 mg/mmole = 15.694 rather than 12.839?
GH is defined in terms of CaO, but I think KH is actually defined in
terms of CaCO3, with 1 KH ~ 17.86 ppm CaCO3. However, the way you did
the calculations, that makes no difference.
This is actually a fairly long-standing controversy. I summarized some
of what I could find about the different constants used in the formulas
and who used what in the letter at
http://www.actwin.com/fish/aquatic-plants/month.9707/msg00222.html
Briefly, the lower constant has been in use for a long time, but some of
us use the higher constant.
We have additional uncertainty in the value of pK1 and in our pH and
alkalinity measurements, so the 22% difference in the constants may not
be as important as it looks.
Roger Miller