- #1
Maharg
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Homework Statement
In natural water containing 0.9 mmol/L calcium and 12 ug/L fulvic acid, determine the
fraction of the fulvic acid that is bound to calcium (i.e. the ratio between the concentration of Ca-FA and total concentration of FA binding sites), assuming that calcium is the only metal presentin a significant concentration.
The pH of the water is 5.0, the conditional stability constant Kf (Ca-FA) is 1.2x103 and the
binding sites on FA is 5 mmol/g.
Homework Equations
FA = H+ + Org-
Org- + Ca2+ = Org-Ca2+
H2O = H+ OH-
Told to find ratio Ca-Org-/Org-
The Attempt at a Solution
Found concentration of FA binding sites = 60 umol/L
then concentration H+ = 50 umol/L
and Ca2+ = 900 umol/L
The professor told us we'll need those reactions but I'm unsure why we need the Water reaction.
Also confused how to get A- as we don't know the equilibrium constant for Fa = H+ + Org- and I've looked it up to see if fulvic acid is strong to find out if it dissociates completely. I don't the next step. If someone could just suggest how I properly do the next step.
I think I have to eventually do Kf = Org-Ca2+/[Org-][Ca2+]