Empirical Formulas

• Empirical formulas are the simplest formula of a compound
• They only show the simplest , not actual atoms

Ex.

• The empirical formula for chlorine gas is Cl
• Dinitrogen tetraoxide ≠ N2O4

To determine the empirical formula we need to know the ratio of  each element.

To determine the ratio, fill in the table below for each problem.

Ex:

Atoms	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	5.6	16.0	0.35	1	1

C2H6O
Determine the empirical formula of a compound containing 24.74% potassium, 34.76% manganese, and 40.50% oxygen.

Atoms	Mass	Molar Mass	Moles	Moles/smallest mole	Ratio
K	24.74	39.1	0.63	1	1
Mn	34.76	54.9	0.63	1	1
O	40.50	16.0	2.53	4	4

KMnO4

• 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, 0.66	3
0.25, 0.75	4
0.2, 0.4, 0.6, 0.8	5

Ex:
Determine the empirical formula of a compound that is 50.5% carbon, 5.26% hydrogen, and 44.2% nitrogen.

Atoms	Mass	Molar Mass	Moles	Moles/smallest mole	Ratio
C	50.5	12.0	4.21	1.33 X 3	4
H	5.26	1.0	5.26	1.66 X 3	5
O	44.2	16.0	3.16	1 X 3	3

C4H5O3

Here is a video that explains molecular and empirical formulas. 

-Benedict Suratos