[Dawson]

I have to write a procedure proposal for how to prove that a sample of chromite contains magnesium, iron, and chromium.
Chemicals provided:

• Iron(III) nitrate, solid
• Chromium(III) nitrate, solid
• 1.00 M HCl solution
• 4 M NaOH solution
• Zinc metal

Equipment:

• Temperature probe
• pH probe and drop counter
• Spectrophotometer and cuvettes
• Normal lab glassware and equipment

I think that I know how to begin this lab, but I am not sure where to go next. I also would like to know if my thinking so far is correct, so feel free to correct anything that I say.

The research that I've done indicates that chromite is either or . Based on what the purpose of this lab is (to prove that a sample contains Mg, Fe, and Cr), I assumed that the sample would contain both and .

My lab notes that zinc and chromium are amphoteric but iron and magnesium are not, so I figured that placing the sample in NaOH would leave me with iron and magnesium precipitates and in solution.

My next thought was that I could dissolve the iron and magnesium in the HCl to yield and and then use the spectrophotometer to prove that this solution does indeed contain Mg and Fe. I'm not sure if this is the proper step to take, but this is the only thing that I can think of. Would this work?

Somehow I would also have to prove that there is chromium present; I thought that I could somehow cause a precipitate to...precipitate xD  but I haven't figured out how to make that happen.

Obviously I'm a little confused as to the use of the Iron(III) nitrate and Chromium(III) nitrate, as well as the zinc, so I think that I'm seriously missing something. Any tips on where I should go from here? I feel like I have not been taught enough in class to deal with this lab, so any additional information that it seems like I haven't thought of is more than welcome.