12.66 g of calcium are heated in air,17.73 g of calcium oxide is formed.The percent oxygen in the co

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12.66 g of calcium are heated in air,17.73 g of calcium oxide is formed.The percent oxygen in the compound is?

17.73g Calcium oxide - 12.66g Calcium = 5.07g Oxygen

Mass of the element / Mass of the compound * 100%
= 5.07g O / 17.73g CaO2 X 100%
= 28.6% of Oxygen in the compound

Check Your Work
Mass of the element / Mass of the compound X 100%
= 12.66g Ca ÷ 17.73g CaO2 X 100%
= 71.4% Ca

71.4% Ca + 28.6% O = 100% CaO2