Question

Caluculate the mass of ferrous ammonium sulfate (Fe(NH4)2(SO4)2.6H2O) you would need to add to a 4.0 mL volumetric flask to make a solution that is 75 ppm.

I've already identified that Fe is 14.24% of the Mohr's salt, but how would the conversion of that go to ppm? Ppm is mg/L, correct?

Answer 1

Yes, ppm is mg/L. Do you really man 4.0 mL? That isn't much volume and I didn't even know they made 4.0 mL volumetric flasks. So 75 ppm will be 75 mg/L or
75 x 4/1000 = 0.3 mg Fe.
0.3 mg Fe x (molar mass Mohr's salt/atomic mass Fe) =

Answer 2

Its some randomly generated question in preparation for a lab with normal sized vol. flasks. But yes, I agree, that would be a bit awkward to have a 4.0 mL flask. Haha

Can explain the unit conversions in the 75 x 4/1000 you posted?

Answer 3

You want 75 ppm. That is 75 mg/L. But you don't need a L; you need only 4 mL so convert 75 mg/L to ?mg/4 mL and that is 75 x 4/1000 = ? mg in 4 mL.