Hi quick question.

So i was asked to find the Concentration of the Standard of PbCrO4(Powder form), this compound is run by using 10-20mg of PbCrO4 and 2.5g of sand is added and is diluted to 100mL in a volumetric flask and is ran on a IC and the result is multiplied by a factor of 40. Last time this was ran we reported a value of 278mg/kg, so what we want to find out is the true value of PbCrO4, and we mostly want the hexavalent chromium. I don't see how this can be calculated using for example c1v1v=c2v2. This is a reagant used with EPA method 3060A. I have read through the epa method several times, with no help. Maybe I'm over looking something.

I have tried calculating it this way

ex. we use 20mg starting = 0.002g/323.2g(PbCrO4) *51.9961 *40(our factor)= 0.01287 (this is low)

Maybe I'm calculating it wrong, or I don't have the right equation.

Any help is appreciated Thanks