Acompound weighing 115 g contains 68.3 g of carbon, 13.2 g of hydrogen, 15.9 g of nitrogen, and some amount of oxygen. what is the mass percent of oxygen in the compound?

Given the total mass of the compound, we can determine directly the amount of oxygen from the determined masses of other elements, carbon, hydrogen, and nitrogen. The mass of oxygen is 115 g- (13.2+68.3+15.9)g which is 17.6 g oxygen. To get the mass percent, divide 17.6g by 115 g and multiply by 100%. This is equal to 15.30%. 

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