Hey there. To start, I have really gotten the concept of moles / mass percent, etc. very well. I'm really stumped on a question however, and would really like some help figuring out the plan of attack. I don't want the answer, just the direction. Here's the question:
Hemoglobin, a protein in red blood cells, carries O2 from the lungs to the body's cells. Iron (as ferrous ion, Fe2+) makes up 0.33 mass % of hemoglobin. If the molar mass of hemoglobin is 6.8x104 g/mol, how many Fe2+ ions are in one molecule?
I've attacked this several ways and I'm just stuck. Can anyone offer some pointers?