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Empirical and Molecular Formula

__Empirical formula,__ gives the lowest term ratio of atoms (moles) in the formula
*All ionic compounds are empirical formulas
Example:
C4H5 (butane) --> molecular formula
C2H5 --> empirical formula of butane
Example:
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
55.8g 16.0
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
Check out this link!
http://www.youtube.com/watch?v=gfBcM3uvWfs
-Lauren
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