Chemistry
Introduction to Empirical and Molecular Formula Problems
CJB-2011
Classwork Practice Problems
Name: ______________________________________ Date: ____________ Block: ____
Empirical Formula-the formula for a substance which tells the relative number of atoms
of each element it contains in lowest whole number ratio. The empirical formula H 2O
indicates that water contains two H atoms for each O atom. This ratio also applies on the
molar level: 1 mole H2O contains 2 mol of H atoms and 1 mol of O atoms.
#1) Ascorbic acid (vitamin C) contains 40.92% C, 4.58 % H, and 54.50% O by mass.
What is the empirical formula of ascorbic acid?
#2) Part A. A 5.325-g sample of methyl benzoate, a compound used in the manufacture
of perfumes, is found to contain 3.758 g of carbon, 0.316 g of hydrogen, and 1.251 g of
oxygen. What is the empirical formula of this substance?
B) What is the molar mass (g/mole) of the empirical formula from the previous question?
C) If Compound X had the empirical formula from Part A, and the molar mass of
Compound X is 612 g/mole, what is the molecular formula for Compound X?
D) Which compounds below would not have the same empirical formula from Part A?
a. C8H8O2
b. C16H16O4
c. C10H11O5
d. C80H80O20
E) Several compounds have been analyzed and their molar masses determined. Which of
the following molar masses if any could not have the same empirical formula from Part
A?
a. 340 grams b. 1564 grams c. 748 grams d. 215 grams e. 674 grams
NOW YOU TRY…
#3) Mesitylene, a hydrocarbon that occurs in small amounts in crude oil, has an empirical
formula of C3H4. The experimentally determined molecular weight of this substance is
121 amu (equivalent to 121 grams on molar scale). What is the molecular formula of
Mesitylene?
#4) Isopropyl alcohol, a substance sold as rubbing alcohol, is composed of C, H, and O.
Combustion of 0.255g of isopropyl alcohol produces 0.561 g of CO 2 and 0.306 g of H2O.
Determine the empirical formula of isopropyl alcohol.
#5) Caproic acid, which is responsible for the foul odor of dirty socks, is composed of C,
H, and O atoms. Combustion of a 0.225-g sample of this compound produces 0.512 g
CO2 and 0.209 g H2O. What is the empirical formula of caproic acid?
b) Caproic acid has a molar mass of 116g/mol. What is its molecular formula?