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Percent Composition

Percent Composition. Percent Composition by Mass – If you want to know what percentage of a compounds’ mass is contributed to by each element present. +. +. Example: If you have a box containing 100 golf balls and

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Percent Composition

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  1. Percent Composition

  2. Percent Composition by Mass– If you want to know what percentage of a compounds’ mass is contributed to by each element present. + +

  3. Example: If you have a box containing 100 golf balls and 100 ping pong balls, which type of ball contributes the most to the MASSof the box? • The same principle applies to finding the % composition of a compound. Different elements have different masses and this must be taken into consideration.

  4. Why chemists use it? • To figure out which compounds are the best sources of an element. • What if I wanted to use potassium oxide as a source of oxygen, it would be helpful to know the % of oxygen is in the compound.

  5. How to find the percent composition of a compound: • Write a correct formula for the compound. • Find the molar mass of the compound. (calculated from the periodic table) • Divide the total atomic mass of EACH ELEMENT by the molar mass of the compound. • Multiply by 100 to convert your results to a percent. • Express your answer to TWO decimal places and don’t forget the % sign

  6. Formula: molar mass of element in sample of compound X 100 molar mass of sample of compound = % composition of element in compound

  7. Example 1: Find the percent composition of oxygen in potassium oxide.

  8. K+1 + O-2 = K2O

  9. Molar Mass • K (2 X 39) = 78 + • O (1 X 16) = 16 = 94g/mol

  10. Percent Composition • % K = 78 X100% = 82.98 % K 94 • % O = 16 X100% = 17.02 % O 94 Always check your work. Your percentiles should add up to 100%

  11. Example 2: Find the percent composition of copper (I) sulfate.

  12. Cu+1 + SO4-2 = Cu2SO4

  13. Molar Mass • Cu (2 X 63.5) = 127 + • S (1 X 32) = 32 + • O (4 X 16) = 64 = 223g/mol

  14. Percent Composition • % Cu = 127 X100% = 56.95 % Cu 223 • % S = 32 X100% = 14.35% 223 • % O = 64 X100% = 28.70 % O 223

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