Percent Composition

Today after a long winters nap, Mr Doktor's E block Chemistry class met once again. The topic of today was percent composition, or what percentage of a compound comes from each element. The basic rule is:

• The percentage by mass of an element in a compound is ALWAYS the same

To find percent by mass, determine the mass of each element present in one mole of the compound.

For example:
NaCl has a total atomic mass of 58.4g/mol(22.9 +35.5)
To find the percent of Na in one mole of NaCl, divide Na's atomic mass by the atomic mass of NaCl
                                  
                                    22.9/58.4= .392= 39% Na

Ex 2:
           You have a 10g sample of H2O. How many grams of Hydrogen are there?

H2O=18g/mol       H2=2g/mol       2/18=.09   (.09)(10)=.9gH

Thats all for today folks and have a............