Formula+Weights

=__Formula Weights__=

Chemical formulas and chemical equations both have quantitative significance, with the subscripts and coefficients representing precise quantities. Formula Weight is the sum of the atomic weight of all atoms appearing in a given chemical formula. The formula weight of a molecule can also be called a molecular weight. For an ionic compounds the term formula unit is used.

Formula weight of H2SO4 = 2 (1.01 of H) + (32.1g of S) + 4 (16.0g of O) = 2 (1.01 amu) + 32.1 amu + 4 (16.0 amu) = 98.1 amu



Percentage Composition
The percent composition of a compound is the percentage of mass which is contributed by each element in a substance to the whole substances total mass. These procedures can be used to verify the purity of of a compound by comparing the calculated percentage composition of the substance to the experimental percent composition. The calculations use formula weight of the substance, the atomic weight of the of the specific element of interest and the number of atoms of that element in the chemical formula of the substance. The following equation is used.

[[image:chem.jpg width="916" height="295"]]
= = http://en.wikipedia.org/wiki/Formula_weight http://www.britannica.com/EBchecked/topic/213920/formula-weight