iron in sample

Solution Preview

First, we have to do is find the molar mass of ferrous ammonium sulfate hexahydrate in order to determine how much actual Fe is in the standard solution.

I calculate it as 296.1 g/mol. Check this out yourself.

Next, we need to find out what percentage the Fe is of the whole compound. Molar mass of Fe is 55.847 g/mol. Therefore,

(55.847/296.1) x 100% = 18.86%

Therefore, if we put in 70.2 mg (0.0702 g) of the compound, we have only 18.86% of that as Fe, right? That means we have:

70.2 mg x 0.1886 = 13.24 mg Fe(II) in the 1 L flask.

Therefore, the concentration of Fe(II) in that flask is:

13.24 mg/1000 mL = 0.01324 mg/ml

Now, we work through the dilutions.

The 1st standard solution results from taking 1 mL of this stock solution and diluting to 100 mL. That's a 1:100 ...