[zeshkani_usa]

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

 

[Hunter2]

The Problem is the soloubility of lead chromate is very poor. Check a table then you can find 0.006 mg/100ml at 25° C. The soloubility product is 3 x 10^-13 (mol/l)²

Your values 10 -20 mg you never can find.

[AWK]

20 mg = 0.02 g

[Hunter2]

And? 0.02 g still larger than 0.006 mg.