Empirical formula

Empirical formula

This topic is taught at both GCSE and at A level.

Definition: The empirical formula is the simplest whole number ratio of atoms of each element in a compound.

Hydrogen peroxide has a molecular formula of H2O2. Whilst its Empirical formula is HO. Benzene has a molecular formula of C6H6. Whilst its Empirical formula is CH. An empirical may not actually exist in real life, its just a way of cancelling the number of atoms on a piece of paper.

So the questions will either ask you to cancel an existing formula like above or they will give you percentages or masses of elements in a compound.

Four step process to dealing with an empirical formula question:

1. Put the elements at the top of the page

2. Put the masses or % under each element

3. Divide by atomic mass

4. Then divide by smallest.

However, there are a few sneaky questions and tricks that they can use. I will show you them in videos. As the videos progress they show progressively harder questions.

1. Calculate the empirical formula of a hydrocarbon that contains 85.7% carbon and 14.3% hydrogen.




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