What is the mole ratio of chromium to nickel atoms in this steel?

Question

The gleaming metallic appearance of the Gateway Arch in St. Louis, Missouri, comes from the stainless steel used in its construction. This steel is made mostly of iron, but it also contains 19% (by mass) chromium and 9.0% (by mass) nickel. What is the mole ratio of chromium to nickel atoms in this steel?

Answer 1

19% by mass chromium and 9.0% by mass nickel means that for every 100 g of material, there will be 19 g of chromium and 9 g of nickel. So, let's now convert those masses to moles:

19 g Cr x 1 mole Cr/52 g = 0.365 moles Cr in 100 g of material

9.0 g Ni x 1 mole/59 g = 0.153 moles Ni in 100 g of material

mole ratio of Cr : Ni = 0.365/0.153 = 2.39 = 2.4 : 1 (rounded to 2 significant figures)