Empirical and Molecular Formulas
Name ____________________________ Date _____________
How to write the empirical formula
1) Assume that ______________________________ equal _____________________ and change ____________
2) Convert all elements’ ________________ to __________________ using _________________
3) Divide all values by the ___________________ mole value
4) Numbers in step 3 become the _____________________ for those elements. However, if it is a decimal mixed
number then ________________ ALL values by some number to make that one whole.
Ex. 1.5 x _______ =
1.33 x _______ =
1.25 x _______ =
Example problems
A) An oxide of chromium is found to have the following percent composition: 68.4% Cr and 31.6% 0. Determine
this compound’s empirical formula.
B) A 60.00 g sample of tetraethyl lead, a gasoline additive, is found to contain 38.43 g lead, 17.83 g carbon, and
3.74 g hydrogen. Find its empirical formula.
How to write the molecular formula
1) Calculate ____________________________________
2) Divide the _____________________________ by the __________________________________
3) Multiple the formula _____________________ by this value
Example problems
A) Empirical formula of a substance is CH2O. Molar mass is 180. What is the molecular formula?
B) A compound containing 5.9265% H and 94.0735% O has a molar mass of 34.01468 g/mol. Determine the
empirical and molecular formula of this compound.
Practice
1) Determine the empirical formula of a compound that contains 17.15% carbon, 1.14% hydrogen, and 81.41 %
fluorine.
2) A sample contains 7.10 grams of Cl, 2.40 grams of C and .603 grams of H. What is the empirical formula?
3) Calculate the empirical formula of a sample of cisplatin is 65.02% platinum, 9.34% nitrogen, 2.02% hydrogen
and 23.63% carbon.
4) Determine the molecular formula of a compound with an empirical formula of NH2 and a molar mass of
32.06g/mol.
5) The empirical formula for a compound is determined to be CH3. If the molar mass of the compound is
30g/mol, what is the molecular formula?
6) A sample is 40.00% C, 6.713% H and 53.28% O on a mass basis and a molar mass of approximately 180
g/mol. (you need to calculate the empirical AND molecular formulas!)