Percent composition

- percentage by mass of a "species" in a chemical formula

Ex: what percentage composition of CO2
*assume you have one mole
  CO2 = 44g/mole
  C     = 12g/mole----12g/mole/(44g/mole) x 100%=27.3%
  O    = 32g/mole-----32g/mole/(44g/mole) x 100%=72.3%

*percent composition of a compound tells you which elements are in the compound how much of each here is
Ex: calculate % composition of
-Cu(NO3)2
 Cu(NO3)2 =  63.5g+28g+96g=187.5g/mole
 Cu   63.5g/ 187.5g=33.9%
 N     28g/187.5g=14.9%
 O     96g/187.5g=51.2%