ktelfeya Posted May 5, 2015 Share Posted May 5, 2015 Hello, I am trying to calculate the percent of each vanadium species as a function of the total vanadium concentration for a particular groundwater sample (script is attached). However, when I sum all the V species predicted, the sum of their concentrations is lower than total input V concentration. For the sample attached, the total V concentration is 0.19 nmol/kg, but the sum of the predicted species is 0.17 nmol/kg, or 22 pmol/kg lower. There is probably something obvious I am missing, but I have not encountered this problem before. Thank you! Kat Peeler.sp8 Quote Link to comment Share on other sites More sharing options...
Brian Farrell Posted May 5, 2015 Share Posted May 5, 2015 Hi Kat, When comparing the mass of a component to the masses of species making up that component, you need to account for the stoichiometry of each species. Taking the V+++ component as an example, the V+++, VO2(OH)2-, and VO3OH-- species are each composed of one mole of V+++. Other species, like (VO)2(OH)5-, (VO)2(OH)2++, and V2(OH)2++++, are composed of two moles of the V+++ component. Before you add up species concentrations in Excel, you need to multiply the concentration of each by the number of moles of the component which go into it. In your case, (VO)2(OH)5- is the third most abundant species, with a concentration of .022 nmol/kg. By not accounting for the fact that this species (along with the others I mentioned) is composed of two moles of V+++, your sum works out to 0.168 instead of 0.19 nmol/kg, which is the total you entered on the Basis pane. For a reference on the subject, try checking out section 3.3.3, Mass balance equations, in the Geochemical and Biogeochemical Reaction Modeling text. Hope this helps, Brian Farrell Aqueous Solutions Quote Link to comment Share on other sites More sharing options...
ktelfeya Posted May 7, 2015 Author Share Posted May 7, 2015 Hi Brian, Thanks so much. That makes perfect sense! kat Quote Link to comment Share on other sites More sharing options...
Jason_Nolan Posted May 27, 2015 Share Posted May 27, 2015 Brian, I would have to say with a response like that, it is time you make the decision to continue on and get that final degree...a very well balanced answer (intended). Quote Link to comment Share on other sites More sharing options...
Brian Farrell Posted May 28, 2015 Share Posted May 28, 2015 Thanks Jason. Someday, perhaps. Right now I'm in a good place where I feel I can make a big impact. Cheers, Brian Quote Link to comment Share on other sites More sharing options...
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