Empirical formula, gives the lowest term ratio of atoms (moles) in the formula
*All ionic compounds are empirical formulas
C4H5 (butane) --> molecular formula
C2H5 --> empirical formula of butane
Consider, 10.87g of Fe and 4.66g of O. What is the empirical formula?
1) First convert from g to moles.
10.87 Fe x 1 mole = 0.195moles 4.66 O x 1mole = 0.291moles
2) Divide both by the smallest molar amount.
Fe 1 <--0.195/ 0.195
O 1.5 <--0.195/0.291
3) Scale ratios to whole numbers.
Fe 1 x 2 = 2
O 1.5 x 2 = 3 Which becomes: Fe²O³
Molecular formula, is a multiple of the empirical formula and it shows the real amount of atoms that combine to form a molecule.
Calculating a multiple:
n= molar mass of the compound
molar mass of the empirical formula
Try some practice questions:
Find the empirical formulas from the given information.
1) 9.37g of Fe and 13.2g of O
2) 8.64g of Li, 11.1g of C, and 2.43g of H
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