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Example Question - 2

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 2:2.406g of calcium combines with 4.16g of chlorine to form a compound.

element	Ca	Cl
ratio of moles	2.406 40.1	4.16 35.5
	0.06	0.117
simplest whole number ratio	1	2

The empirical formula of the compound formed is CaCl₂.

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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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