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Example Question - 1

The empirical formula can be calculated using chemical analysis to determine the mass of each element in a compound or the percentage composition by mass of each element in a compound. This can be used to find the number or relative number of moles of each element by dividing the mass or percentage mass by the relative atomic mass. This can then be converted into a whole number ratio in its simplest terms.Example 1:75% by mass of a compound is carbon and 25% by mass is hydrogen.
elementCH
ratio of moles75
12		25
 1
6.2525
simplest whole number ratio 14
The empirical formula is CH4

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Specification: AQA Chemistry (7404), AS-level, 3.1.2.4 Empirical and molecular formula. Topic: Amount of Substance.

Key terms in this lesson

Relative atomic mass
The weighted mean mass of an atom of an element compared to 1/12th the mass of a carbon-12 atom.
Mole
The amount of substance that contains as many particles as there are atoms in exactly 12g of carbon-12.
Empirical formula
The simplest whole number ratio of atoms of each element in a compound.

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All 33 lessons in Amount of Substance · All AQA AS-level Chemistry topics