SS1 Chemistry Lesson Note on Empirical and Molecular Formulae

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EMPIRICAL AND MOLECULAR FORMULAE

Empirical formula is the simplest formula which gives the ratio of the number of different atoms present in a compound. It does not give the exact number of each atom whereas the molecular formula gives the exact number of the atoms present in a molecule of a compound.

The molecular formula of a compound is a whole number multiple of its empirical formula.

Examples:

Find the empirical formula of a compound which on analysis yields the following as the reacting masses carbon= 2.0, hydrogen=0.34g, Oxygen = 2.67g. From your result find the molecular formula of the compound. If it’s relative molecular mass is 60. (C=12, H=1, O=16)

Solution:

(CH₂O)_X = 60

(12 + (2×1) + 16)_x =60

(12+2+16)x = 60

(30)x = 60

X =  2

Molecular formula is, therefore (CH₂O)₂

=C₂H₄O₂ or CH₃COOH

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