# chem module 5 lesson 2

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• You should then find the molar mass of each element. To find the percent by mass you should divide the molar mass of the element by the total molar mass of the compound. Finally you must  multiply the previous answer by 100.
• To find percent by mass you should first find the total molar mass of the compound. ﻿
• Let's find the percent by mass of ﻿water,H20.
• The molar mass of Oxygen is 16.00. The molar mass of Hydrogen is 1.008, we must multiply 1.008 by 2 too find the total molar mass because there are 2 Hydrogen atoms. The total molar mass of H20 is 18.016.﻿
• To find the percent by mass for Hydrogen you should divide the molar mass of Hydrogen (2.016) by the total molar mass (18.016) and then multiply by 100. The percent by mass for Hydrogen is 11.19%.
• Now to find the percent by mass for Oxygen, you should divide the molar mass of the element (16) by the total molar mass (18.016), then multiply this by 100 to get 88.8 percent.
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