the empirical formula for Chlorine gas is Cl.
Dinitrogen tetraoxide: N2O4 ---- NO2
Molecular formulas give the actual number of atoms.
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:
Atom Mass Molar Mass Moles Mole-smallest mole Ratio
Example: A sample of an unknown compound is found to contain 8.4g of 'C', 2.1g of 'H', and 5.6g of 'O'. Determine the empirical formula.
Atom Mass Molar Mass Moles Mole-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
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
Example: Determine the empirical formula of a compound that is 50.5% C, 5.26% H, and 44.2% N.
Atom Mass Molar Mass Moles Mole-smallest mole Ratio
C 50.5 12.0 4.21 1.32 4
H 5.26 1.0 5.26 1.66 5
N 44.2 14.0 3.16 1 3
Molecular Formula
If you know an empirical formula, to find the molecular formula you need the molar mass.
Example: The empirical Formula for a substance is CH2O and its molar mass is 60.0g/mol. Determine the molecular formula.
Empirical Molecular
Formula CH2O C2H4O2
Molar Mass 30.0g/mol 60.0g/mol
By: Crystal Pan
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