Wednesday, 15 May 2013

1.24 calculate empirical and molecular formulae from experimental data

Empirical Formula

The empirical formula of a compound gives the simplest whole-number ratio of atoms of each element in a compound.
It can be calculated from knowledge of the ratio of masses of each element in the compound.

e.g. A compound that contains 10g of hydrogen and 80g of oxygen has an empirical formula of HO.

This can be shown here:

Amount of hydrogen atoms= mass in grams ÷ Ar of hydrogen = (10 ÷ 1)= 10 mol
Amount of oxygen atoms= mass in grams ÷ Ar of oxygen = (80÷ 16) = 5 mol

Therefore the formula/ratio is 10:5 or simplified to be 2:1


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