Empirical Formula Practice Test Questions

Chemistry Test Questions

The empirical formula of a compound represents the simplest whole number ratio between the elements that make up the compound. This ten question practice test deals with finding empirical formulas of chemical compounds.

You may wish to review this topic before taking this test by reading the following:

How to Find the Molecular Formula and Empirical Formula
How to Calculate the Empirical and Molecular Formula of a Compound

A periodic table will be required to complete this test. Answers for the practice test appear after the final question.

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Question 1

Sulfur dioxide
Sulfur dioxide may be represented using its empirical formula. Science Photo Library / Getty Images
What is the empirical formula of a compound containing 60.0% sulfur and 40.0% oxygen by mass?
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Question 2

A compound is found to contain 23.3% magnesium, 30.7% sulfur and 46.0% oxygen. What is the empirical formula of this compound?
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Question 3

What is the empirical formula for a compound containing 38.8% carbon, 16.2% hydrogen and 45.1% nitrogen?
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Question 4

A sample of an oxide of nitrogen is found to contain 30.4% nitrogen. What is its empirical formula?
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Question 5

A sample of an oxide of arsenic is found to contain 75.74% arsenic. What is its empirical formula?
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Question 6

What is the empirical formula for a compound containing 26.57% potassium, 35.36% chromium, and 38.07% oxygen?
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Question 7

What is the empirical formula of a compound comprised of 1.8% hydrogen, 56.1% sulfur and 42.1% oxygen?
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Question 8

A borane is a compound containing only boron and hydrogen. If a borane is found to contain 88.45% boron, what is its empirical formula?
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Question 9

Find the empirical formula for a compound containing 40.6% carbon, 5.1% hydrogen, and 54.2% oxygen.
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Question 10

What is the empirical formula of a compound containing 47.37% carbon, 10.59% hydrogen and 42.04% oxygen?

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Answers

1. SO3
2. MgSO3
3. CH5N
4. NO2
5. As2O3
6. K2Cr2O7
7. H2S2O3
8. B5H7
9. C2H3O2
10. C3H8O2

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Empirical Formula Tips

Remember, the empirical formula is the smallest whole number ratio. For this reason, it's also called the simplest ratio. When you get a formula, check your answer to make sure the subscripts can't all be divided by any number (usually it's 2 or 3, if this applies). If you're finding a formula from experimental data, you probably won't get perfect whole number ratios. This is fine! However, it means you need to be careful when you're rounding numbers to make sure you get the correct answer. Real world chemistry is even trickier because atoms sometimes participate in unusual bonds, so empirical formulas aren't necessarily accurate.