Name Date

Chemistry – Unit 5 Worksheet 2

Empirical and Molecular Formulas

Empirical means based on laboratory evidence. The empirical formula of a compound is the simplest whole number ratio of the atoms present in a molecule. This can be figured out in two different ways: with masses of the elements or with percent composition. Follow the steps below in order to find an empirical formula:

1.

2.

3a.

3b.

Find the empirical formula of a compound containing 4.9 g of magnesium and 32.0 g of bromine

Find the empirical formula of a compound that is 70.0% iron and 30.0% oxygen.

Complete the following problems. Make sure to show all of your work and units!

1. What is the empirical formula of a carbon-oxygen compound, given that a 95.2 g sample of the compound contains 40.8 g of carbon and the rest oxygen?

2. A compound was analyzed and found to contain 9.8 g of nitrogen, 0.70 g of hydrogen, and 33.6 g of oxygen. What is the empirical formula of the compound?

The molecular formula of a compound is the actual formula (not the simplest ratio). In order to do this, follow the steps below:

1.

2.

3.

****

4.

A compound composed of hydrogen and oxygen is found to contain 0.59 g of hydrogen and 9.40 g of oxygen. The molar mass of this compound is 34.0 g/mol. Find the empirical and molecular formulas.

Try the following problems. Be sure to show all your work & units.

1. A sample of iron oxide was found to contain 1.116 g of iron and 0.480 g of oxygen. Its molar mass is roughly 5 x as great as that of oxygen gas. Find the empirical formula and the molecular formula of this compound.

2. A compound is 75.46% carbon, 4.43% hydrogen, and 20.10% oxygen by mass. It has a molecular weight of 318.31 g/mol. What is the molecular formula for this compound?

Modeling Chemistry 1 U5 ws 2 v2.0