Name:_____________________________________________________________________________________________________________
Empirical and Molecular Formula Notes (Unit 6.6 and 6.7)
EMPIRICAL FORMULAS
 Consists of the __________________ for the elements combined in a compound, with subscripts showing the
____________________ whole-number __________________ of the different atoms in the compound.
 Huh?!?
 In other words, its a chemical formula in the simplest _____________.
 C2H6 → ___________
EMPIRICAL FORMULAS FROM PERCENT COMPOSITION
 1) Convert the percent to _____________.
 2) Convert grams to __________________ by dividing by the molar mass of each ______________.
 3) Divide each amount by the ______________ molar value to determine _____________.
 4) Multiply each molar ratio until all elements are ____________________ numbers.
 Example: What is the empirical formula for a compound that is 38.77% Cl and 61.23% O by mass?
EMPIRICAL FORMULA PRACTICE PROBLEM
 A hydrate is analyzed and has a percent composition of 13.5% Ca, 10.8 % O, and 0.675% H. The rest of the
compound is made of water and is not considered relevant. What is the empirical formula of this compound?
MOLECUALR FORMULA
 Whole number _________________ of the empirical formula.
 Gives the _______________ number of atoms in the _________________ not just the simplest ratio.
 Example: A compound has an empirical formula of CH2O, but has a mass of 90.0 g/mol. What is the correct
molecular formula?
MOLECULAR FORMULA PRACTICE PROBLEM
 Hydrogen peroxide is a common household disinfectant. When analyzed, it has a composition of 5.88% H and
94.12% O. It has a molar mass of 34 g/mol. What is the molecular formula for hydrogen peroxide?
Name:_____________________________________________________________________________________________________________
Empirical and Molecular Formula Practice (Unit 6.6 and 6.7)
Directions: write the empirical formula for each of the following compounds.
1) C6H6
2) C8H18
3) WO2
4) C2H6O2
5) X39Y13
6)C2Cl4
Directions: Solve each of the following problems. Be sure to show your work and include sig figs.
7) A compound has an empirical formula of C2OH4 and a molar mass of 88 g/mol. What is the molecular formula of this
compound?
8) A compound has an empirical formula of C4H4O and a molar mass of 136 g/mol. What is the molecular formula of this
compound?
9) A compound has an empirical formula of CFBrO and a molar mass of 254.7 g/mol. What is the molecular formula of
this compound?
10) A compound has an empirical formula of C2H8N and a molar mass of 46 g/mol. What is the molecular formula of this
compound?
11) A well-known reagent in analytical chemistry, dimethlyglyoxime, has the empirical formula C2H4NO. If its molar mass
is 116.1 g/mol, what is the molecular formula of the compound?
12) Nitrogen and oxygen form an extensive series of oxides with the general formula NxOy. One of them is a blue solid
that comes apart in the gas phase. It contains 36.84% N and 63.16% O. What is the empirical formula of this oxide?
13) A sample of indium chloride weighing 0.500 g is found to contain 0.2404 g of chlorine. What is the empirical formula
of indium chloride?
Name:_____________________________________________________________________________________________________________
14) An unknown compound was found to have a percent composition as follows: 47.0% potassium, 14.5% carbon, and
38.5% oxygen. What is its empirical formula? If the true molar mass of the compound is 166.22 g/mol, what is its
molecular formula?
15) Rubbing alcohol was found to contain 60.0% carbon, 13.4% hydrogen and the remaining mass was due to oxygen.
What is the empirical formula of rubbing alcohol?
16) A sample (3.585g) contains 1.388g of C, 0.345g of H, 1.850g O and its molar mass is 62g. What is the molecular
formula of this substance?
17) An unknown sugar is found to have a molar mass of 180.18 g/mol. The sugar contains: 40.0 % C, 6.7 % H and 53.3 %
O. What is the empirical formula of this sugar? What is the molecular formula of this sugar?