Sunday, January 16, 2011

Lesson 20: EMPIRICAL FORMULAS.

  • Empirical formulae are the simplest formulae of a compound.
  • They only show the simplest ratios, not the actual number of atoms.
Molecular formula: C8H18 ----- Empirical formula: C4H9

Empirical formula for a diatomic atom like Cl2 is Cl.

Dinitrogen tetraoxide = Molecular: N2O4 = Empirical: NO2

  • To determine the empirical formula, we need to know the ratio of each element.
  • A sample of an unkown compound is foundto contain 8.4 g of C, 2.1 g of H and 5.6 g of O. Determine the ratio. Determine the empirical formula. 

    |  Atom   |   Mass   |   Molar Mass   |   Moles   |   Moles/Smallest Mole   |   Ratio   | 
                C            8.4             12.0                 0.7                        2                          2
                H            2.1              1.0                  2.1                        6                          6
                O            5.4             16.0                0.35                       1                          1

Empirical Formula: C2H6O

The simplest ratio may be decimals. For certain decimals you need to multiply everything by a common number.  

                                       DECIMAL       |       MULTIPLYING COEFFICIENT     
                                    0.5                                      2
                            0.33 or 0.66                               3
                            0.25 or 0.75                               4
                         0.2, 0.4, 0.6, 0.8                            5


This guy is awesome..





.. but Mr. Doktor's still the best!




»Loureal Agustin.

posted by chemistry11 @ 10:09 PM

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