Molar Mass & Molar Conversions

  Molar Mass can be defined as the mass in grams(g)of 1 mole in a substance. Therefore, it would be measured with the units grams per mole (g/mol). This number can be determined by looking at the atomic mass on the periodic table as the atomic weight of an element in grams is one mole of that element.

Molar Mass of Compounds
 
The molar mass of compounds is determined by adding the mass of all the atoms in the compound. Here are some steps to follow:


1. Find the individual masses of each element.

EXAMPLE:
H2SO4 -> Hydrogen: 1.0 amu, Sulfur: 32.1 amu, Oxygen: 16.0 amu
H2SO4 -> 1.0 + 32.1 + 16.0

2. Check to see if the number of atoms of each element correspond with the formula. Add any necessary changes.

EXAMPLE:
H2SO4 -> 2(1.0) + (32.1) + 4(16.0)
H2SO4 -> 2.0 + 32.1 + 64.0


3. Add all masses together with proper significant digits and units.


EXAMPLE:
H2SO4 -> 98.1 g/mol
H2SO4 -> 98 g/mol

  There may be cases where you may have to convert between moles and mass. In these cases, use molar mass as your conversion factor.

EXAMPLE:
  Determine the mass(g) in 3 mol of Oxygen.

1. Write out what you know, and what you want to find out.

3 mol of O    x          3(16.0) g          = ? g
                                 1 mol

2. Cancel out anything that you can.

3 mol of O    x          48 g                =? g
                              1 mol

3. Do any more calculations accordingly and write answer with proper significant digits and units.

 3(48g)     = 114 g of O
     1 

  You can do the same when finding the number of moles in a certain number of grams; just place the units in the correct part of an equation and repeat the steps!

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