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How to Get the Percentage of the Elements in a Compound

All matter is made up of atoms. Different types of atoms are called elements, and they are distinguished by the number of protons in their nuclei. Through chemical reactions, atoms bind to other atoms to form molecules or compounds. A particular compound has a specific molecular formula, which shows which atoms are present in each molecule of that compound. Determining the percentage of a particular element in a compound is as simple as dividing the weight of that atom by the weight of the whole molecule.

Things You'll Need

Calculator
Periodic Table of the Elements

Instructions

- 1
  Look for the different chemical symbols in the chemical formula for the compound and write down all the elements it contains. Chemical symbols have either one letter or two, but the first letter is always capitalized.
- 2
  Determine how many of each element are in each molecule of the compound in question. When a chemical symbol is followed by a number, that many atoms of that element are present. When multiple chemical symbols are written in parentheses, any numbers following the parentheses are applied to everything contained within.
- 3
  Look in the periodic table for the atomic mass of each element and write it down alongside your tally from Step 2.
- 4
  Multiply the atomic mass of each element by the quantity of that atom in the compound. This calculation yields the total mass of each element. Write these totals alongside the tally from before.
- 5
  Add all of the results from Step 4 together to get the total mass of the entire compound.
- 6
  Divide the mass of any given element, as calculated in Step 4, by the total mass of the compound. Multiply this number by 100 to get the percentage, by weight, of that element in the compound.

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