1. PERCENT COMPOSITION used to determine the formula of a compound
% by mass of each element
in a compound
% of element E in a compound:
%E = total grams of E
MM of compound

2. PERCENT COMPOSITION
If 8.20 g of magnesium combines with 5.40 g of oxygen to form a compound, what is the % comp. of this compound?
60.3% Mg, 39.7% O

3. PERCENT COMPOSITION Calc. % composition of C3H8. 81.68% C, 18.32% H
Calc. % comp of each element in sodium bisulfate.
19.15% Na, 0.841% H,
26.71% S, 53.30% O

4. EMPIRICAL FORMULA
lowest whole-number ratio of atoms of the elements in a cmpd.
ionic: always empirical
molecular: usually not empirical
ex: C2H6
empirical formula: CH3

5. EMPIRICAL FORMULA
Calc. the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen.
N2O5

6. EMPIRICAL FORMULA steps: change % to g convert g to moles
divide each number of moles by the smallest number
determine lowest whole numbers (multiply by common factor)

7. EMPIRICAL FORMULA
Calc. empirical formula of a cmpd that is 52.1% C, 13.2% H and 34.7% O.
C2H6O