% Composition, Empirical and Molecular Formula Worksheet
1) How many grams of hydrogen are in 84.5 g of Ca(OH)2?
2) A compound with an empirical formula of C2OH4 and a molar mass of 176 grams per mole. What is the molecular formula of this
compound?
3) A compound with an empirical formula of C4H4O and a molar mass of 68 grams per mole. What is the molecular formula of this
compound?
4) a) What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29.0% oxygen?
b) If its molar mass is 110 grams per mole, what is the molecular formula?
5) a) What’s the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0% oxygen?
b) If the molar mass of this compound is 73.8 grams per mole, what is the molecular formula?
c) What is the name of this compound?
Answers:
1) How many grams of hydrogen are in 84.5 g of Ca(OH)2?
% H in Ca(OH)2 = 2.02/74.1 x100 = 2.73%
2.73% of 84.5 g = .0273 x 84.5 g = 2.31 g of hydrogen
2) A compound with an empirical formula of C2OH4 and a molar mass of 176 grams per mole. What is
the molecular formula of this compound?
C2OH4 = 44.06 grams / mole
176/44=4 so
C8O4H16
3) A compound with an empirical formula of C4H4O and a molar mass of 68 grams per mole. What is
the molecular formula of this compound?
C4H4O = 68.08 grams / mole
68/68=1 so
C4H4O
4) a) What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29.0%
oxygen?
b) If its molar mass is 110 grams per mole, what is the molecular formula?
a) C 65.5 ( 1mole /12.01g) = 5.454 / 1.813 = 3
H 5.5 ( 1 mole / 1.01g) = 5.446 / 1.813 = 3 so C3H30 molar mass = 55.06
O 29.0 ( 1 mole / 16.00 g) = 1.813 / 1.813 = 1
b) 110 / 55.06 = 2 so C6H602
5) a) What’s the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0%
oxygen?
b) If the molar mass of this compound is 73.8 grams per mole, what is the molecular formula?
c) What is the name of this compound?
a) Li 18.7 ( 1mole / 6.94g) = 2.695 / 1.357 = 2
C 16.3 ( 1 mole / 12.01g) = 1.357 / 1.357 = 1 so Li2C03 molar mass = 73.89
O 65.0 ( 1 mole / 16.00 g) = 4.063 / 1.357 = 3
b) 73.8 / 73.8 = 1 so Li2C03
c) The name of Li2C03 is Lithium carbonate