Chem Class- November 16

The Empirical Formula:

• Sometimes called the simplest formula
• Is the smallest whole-number ratio of atoms (represented by the subsrcipts)

Molecular formulas are different. They specify how many of each atom there are in a molecule of a compound (represented by the subscripts).

Examples of molecular formulas: P4O10, C6H18O3, N2O4
Examples of empirical formulas: P2O5, C2H6O, NO2

The youtube video we included in the last blog talked about calculating empirical formulas. Basically you:

•  find the mass of each element in the compound
• Find the atomic mass (g/mol)
• Calculate the number of moles
• Divide the number of moles by the smallest amount of moles
• You'll be given a whole number and that is the ratio
• If you are not given a whole number for the ratio here's what you do:

Ratio ends in a decimal of: ~0.5: multipy by 2
Ratio ends in a decimal of: ~0.33 or ~0.6: multiply by 3
Ratio ends in a decimal of: ~0.25 or ~0.75: multipy by 4
Ratio ends in a decimal of ~0.2, ~0.4, ~0.6, ~0.8: multiply of by 5

Also, if you are given a percentage of each element in a compound then assume that you have 100 g of the compound (makes up100%)

That's all there really is to it!:) Just remember that you need the number of moles to solve the problem. We find this helpful: