Finding molecular formula from empirical formula
1. Determine the molecular formula of a compound with the empirical formula CF2 and a molar mass of
200.04g/mol.
2. Calculate the molecular formula of a compound with the empirical formula C2H2O and a molar mass of
126.12g/mol
3. A compound has empirical formula C2H5N and molar mass 86.16g/mol. What is its molecular formula?
Empirical formula from percentage composition
1. Empirical formula for compound that is 48.38% Carbon, 8.12% Hydrogen and 43.5% Oxygen?
2. Eugenol is the major component in oil of cloves. It has a molar mass of 164.2g/mol and is 73.14%
Carbon and 7.37% Hydrogen, the remainder is Oxygen. What are the empirical and molecular formulas
for Eugenol?
3. A sample was analyzed and found to contain 40.0% Carbon, 6.71% Hydrogen and 53.29% Oxygen. If
the molecular weight of the compound is 180.16g/mol. What are the empirical and molecular formulas
of the compound?
Sodium burns in excess oxygen to give a yellow solid oxide that contains 58.97% of sodium.
What is the empirical formula of the oxide?
N.B. This is an oxide of sodium. It must contain only Na and O. Since the percentage of Na is
58.97 that of O must be 100 – 58.97 = 41.03%
A compound P contains 73.47% carbon and 10.20% hydrogen by mass, the remainder being oxygen.
It is found from other sources that P has a Relative Molecular Mass of 98 g mol-1. Calculate the
molecular formula of P.
A hydrocarbon with a Relative Molecular Mass (Mr) of 28 g mol–1 has the following
composition: Carbon 85.7%; Hydrogen 14.3%. Calculate its molecular formula.
A hydrocarbon with a Relative Molecular Mass (Mr) of 42 g mol–1 has the following
composition: Carbon 85.7%; Hydrogen 14.3%. Calculate its molecular formula.
Na 29.1%; S 40.5%; O 30.4% (empirical formula)
H 3.66%; P 37.8%; O 58.5%
Limiting reaction
What is the greatest amount of NH3(in moles) that can be made with 3.2 moles of N2 and 5.4 moles of H2
? Which is the limiting reactant? Which reactant is in excess and how many moles of it are left over?
N2 + 3H2
2NH3
What is the greatest amount of MgO (in moles) that can be made with 7.8 moles of Mg and 4.7 moles of
O2 ? Which is the limiting reactant? Which reactant is in excess and how many moles of it are left over?
2Mg
+ O2
2MgO
What is the greatest amount of AlCl3 (in grams) that can be made with 114grams of Al and 186grams of
Cl2 ? Which is the limiting reactant? Which reactant is in excess, and how many grams of it are left over?
2Al + 3Cl2
2AlCl3
If 9.0g of calcium is allowed to react with 4.1g of oxygen, what is the limiting reagent? Calculate the
theoretical yield of calcium oxide in grams
2Ca
+ O2
2CaO