A number of molecules have the formula C6H13NO. One is a derivative of butane with an attached amino group. Another is a butane derivative with a nitrogen and a hydroxyl group. Others are variations on the acid morpholine, of methanamine or of hexane. The various isomers vary in their chemical properties, but all share the same elemental ratio, and all have the same percentage of oxygen by mass.
Calculate the relative amount of oxygen in the molecule by multiplying 1, which is the number of oxygen atoms in it, by 16, which is oxygen's relative atomic mass: 1 --- 16 = 16.
Calculate the molecule's total relative mass by multiplying 12, 14, 1 and 16, which are the relative masses of carbon, nitrogen, hydrogen and oxygen, by the number of atoms of each in the molecule: (12 --- 6) + (1 --- 13) + (1 --- 14) + (1 --- 16) = 115.
Divide oxygen's relative mass by the total relative mass: 16 ÷ 115 = 0.1391, or 13.91 percent. The molecule contains 13.92 percent oxygen by mass.
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