How to find empirical formula when molecular formula is given

Hey Jyoti,

The molecular formula is always a whole number multiple of the empirical formula.

The empirical formula is by definition the simplest whole number ratio defining constituent atoms in a species. The molecular formula is always a whole number ratio of the empirical formula.

Molecular formula = Empirical formula X n

Where n is the whole number ratio.

To understand the method, let us take an example of glucose, the simplest of all sugars. Supposing we do not know its empirical formula.

To determine the empirical formula of a known substance, such as glucose, we take the subscripts of the molecular formula (C6H12O6) and reduce them to the simplest whole number ratios. If we divide this by 6, we get C1H2O1. (We don't usually write the 1's, so this would be CH2O.)

Now that we know the empirical formula of glucose, we know what the "correct ratios" from elemental analysis should be if we really made glucose. In this case, we have 6 carbons, 12 hydrogens, and 6 oxygens, and the ratios are one carbon and oxygen for every two hydrogens. If the elemental analysis of our sample shows a ratio of one carbon and one oxygen for every two hydrogens, then the analysis is consistent with glucose.

The empirical formula is the ratio between those molecules. So, glucose: C6H12O6 (molecular formula) and C1H2O1 (empirical). As you can see the ratio of carbon to hydrogen to oxygen in glucose is 1:2:1

Remember that a number of different molecules may have the same empirical formula, so this does not prove that what we made was glucose. On the other hand, if the elemental analysis is not consistent with the empirical formula of glucose, then that certainly means that we did not make glucose. For example, let's say we found one carbon for every three oxygens. That would not be consistent with the formula of glucose, and hence, the elemental analysis would prove that we failed in our attempt to make glucose.

I hope I was able to help you. Still, if you have any doubt, feel free to ask.

All the best for the future!