Calculate the number of g of chromium needed to produce 20.00 g of chromium oxide

Answer 1

There are several different form of chromium oxide because of the different possible oxidation states for chromium. Assuming the question is referring to the most common oxide of chromium, Cr₂O₃, we can write the following reaction:

4Cr(s) + 3O₂(g)→2Cr₂O₃(s)

20.00 g Cr₂O₃ x 1 mole Cr₂O₃ / 152 g = 0.1315 moles

moles Cr(s) needed to produce 0.1315 moles of Cr₂O₃:

0.1315 moles Cr₂O₃ x 4 moles Cr / 2 moles Cr₂O₃ = 0.263 moles

grams Cr(s) needed:

0.263 moles Cr x 51.996 g/mole = 13.67 g of Cr needed