You need to make a 1.00 ppm (aqueous) iron standard to calibrate an analytical i

Question

You need to make a 1.00 ppm (aqueous) iron standard to calibrate an analytical instrument. What mass of “FAS” [Fe(NH4)2(SO4)2·6H2O] is needed to make 1.00 L of this solution? Use molar masses from the periodic table in the inside cover of Harris for your calculations. Using commonly available sizes of volumetric flasks (Table 2-3) and transfer pipets (Table 2-4), design a two-step dilution procedure that allows you to start with a larger mass of FAS—enough to get at least four significant figures in the initial weighing. Specify the concentration and volume of your initial stock solution, the mass of FAS you would have to weigh out to make it, and what glassware you would use to dilute it to obtain 1.00 L of 1.00 ppm Fe.

Explanation / Answer

Preparation of solution

1 ppm of 1 L solution of Fe solution using FAS

1 ppm = 1 mg/L

392.13 g FAS has 55.84 g Fe

So for 1 mg (0.001 g) Fe we would take = 0.001 x 392.13/55.84 = 0.007 g

we take 7 mg of FAS to get 1 ppm of Fe standard solution

mass of FAS to be taken =

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