Question Video: Determining an Empirical Formula Given the Ratio of Atoms in a Molecule | Nagwa Question Video: Determining an Empirical Formula Given the Ratio of Atoms in a Molecule | Nagwa

# Question Video: Determining an Empirical Formula Given the Ratio of Atoms in a Molecule Chemistry • First Year of Secondary School

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The numbers of carbon, hydrogen, and oxygen atoms in a molecule are in the ratio 2 : 6 : 2. What is the empirical formula of this molecule?

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### Video Transcript

The numbers of carbon, hydrogen, and oxygen atoms in a molecule are in the ratio two to six to two. What is the empirical formula of this molecule?

An empirical formula is a chemical formula that indicates the elements in a molecule and the simplest whole number ratio of atoms of each element. This is not to be confused with a molecular formula, which is the chemical formula that expresses the exact number of atoms of each element in a molecule. For example, a molecule of glucose has the molecular formula C6H12O6. This means that one molecule of glucose contains exactly six atoms of carbon, 12 atoms of hydrogen, and six atoms of oxygen. This also means that the ratio of carbon to hydrogen to oxygen atoms in the molecule is six to 12 to six.

If we simplified the ratio by dividing by six, the greatest common factor, we would get the simplest whole number ratio, one to two to one. Matching up the ratio with the chemical symbols, we can write the empirical formula, CH2O. So if we know the molecular formula or the ratio of atoms in a molecule, we can determine the empirical formula by dividing by the greatest common factor.

In the question, we are told that the ratio of carbon to hydrogen to oxygen atoms in a molecule is two to six to two. The greatest common factor of two and six is two, so we need to divide each of the values by two to determine the simplest whole number ratio. So the simplest whole number ratio of carbon to hydrogen to oxygen atoms is one to three to one. We can write these values as subscripts after the appropriate element to construct the empirical formula. A value of one is omitted from a chemical formula. Removing these subscripts gives us the empirical formula CH3O.

So a molecule that has a ratio of carbon to hydrogen to oxygen atoms of two to six to two has an empirical formula of CH3O.

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