Calculating the Empirical Formula

What is an Empirical Formula?

The empirical formula represents the smallest whole number ratio of atoms present in a

compound.

Steps for Determining the Empirical Formula of a Compound

1. Obtain the mass of each element present (in grams). If each element is in a percentage, assume

you have a one hundred gram sample.

2. Determine the number of moles of each type of atom present

3. Divide the number of moles of each element by the smallest number of moles to convert the

smallest number to 1. If all of the numbers so obtained are whole numbers, these are the

subscripts in the empirical formula. If one or more are not whole numbers, go on to step 4.

4. Multiply the numbers you derived by step 3 by the smallest integer (usually two) that will convert

all of them to whole numbers.

Video for Calculating the Empirical Formula

Practice Problems for Finding the Empirical Formula

1. Calculate the empirical formula of a compound that is 85.6% C and 14.4% H by mass

2. A compound is analyzed and found to contain 12.1 % carbon, 16.2 % oxygen, and 71.7% chlorine by mass.

Calculate the empirical formula of this compound.

3. A compound contains 40.0% carbon, 6.7 % hydrogen, and 53.3% oxygen by mass. Calculate the empirical

formula.

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