# percent composition

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• We will be learning how to do percent composition﻿ by mass!
• ﻿First, you need to find the molar mass of each individual element. To find the molar mass of an element, add the mass of the element from the periodic table then if there is more than one atom, multiply the mass by the total amount of atoms.  Example of H20: H- 1.008 x 2 = 2.016   O-16.00 g
• Add the elements total molar masses together to find the molar mass of the compound. Remember to round your answers to the correct number of significant figures! Example: H-2.016 +  C-16.00 = 18.016 g
• You will now divide the elements's individual molar mass by the molar mass of the compound and multiply by 100%.  The set up of the equation should look similar to this- total molar mass of the element        x 100% molar mass of the whole compound
• ﻿Now let's try a problem! What is the percent composition by mass of carbon in CaCO3?
• Ca: 40.08 C: 12.01 O:16.00 x 3 = 48 +__________________________ 100.1 g
• 12.01 ____________  x 100%    = 12% 100.1 g
• I hope this lesson helped!﻿
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