Day 6 Empirical and Molecular Formula.notebook
Empirical and Molecular Formulas
April 07, 2016
How do we find the E.F. of a compound?
E.F. is the lowest whole number ratio of elements in a chemical formula
M.F. is a multiple of the E.F.; it is the actual ratio of elements in a real compound.
Using percentage composition data of course!
Example
Substance Molecular Formula Empirical Formula Lowest Ratio 1:1 hydrogen peroxide H2O2 HO water H2O H2O 2:1 glucose C6H12 O6 CH2O 1:2:1 1:1 benzene C6H6 CH acetylene C2H2 CH 1:1 aniline C6H7N C6H7N 6:7:1 Apr 6­9:39 AM
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Example #1:
Find the E.F. of a compound that is 85.6% carbon and 14.4% hydrogen.
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More on Molecular Formula
Recall: Molecular Formula (M.F.) = n x Empirical Formula (E.F.)
where n = 1, 2, 3 ...
E.F. = CH2 O M.F. Molar Mass X 1 Example #2:
Find the E.F. of a compound containing 81.7% carbon and 18.3% hydrogen.
Name of Compound Therefore, if we know the E.F. of a molecule and the molar mass of a molecule, we can determine its M.F. The molar mass of the E.F. can be easily calculated.
M.F. (find) =
E.F. (given)
molar mass of M.F. (given)
molar mass of E.F. (use PT to get it)
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Day 6 Empirical and Molecular Formula.notebook
April 07, 2016
Example #3:
The E.F. of ribose (a sugar) is CH2O. A mass spectrometer was used to determine that the molar mass of ribose is 150 g/mol. What is the molecular formula of ribose?
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