What is the percent of oxygen by mass in a pure sample of fecr2o4?

Answer is:   percent of oxygen by mass in fecr₂o₄  is 28,5%.mr(fecr₂o₄) = ar(fe) + 2·ar(cr) + 4·ar(o)mr(fecr₂o₄) = 55,85 + 2·52 + 4·16mr(fecr₂o₄) = 223,85.ω(o) = 4·ar(o)  ÷ mr(fecr₂o₄)ω(o) = 64  ÷ 223,85ω(o) = 0,285 = 28,5%.fecr₂o₄ - iron  chromium  oxide or iron chromite.

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