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Molar Mass

(Molar Mass, Molecular Weight, Gram Formula Mass)

 

Mole Conversions

 

Definitions

Molar Mass is the mass of one mole of a substance (6.02 x 1023 formula units). The unit for molar mass (note it is the mass of a mole) is grams/mole.

Atomic Weight is the molar mass of an element.

Formula Weight is the molar mass of an IONIC compound.

Molecular Weight is  the molar mass of a COVALENT compound.

Molecular Mass is the mass of a given molecule (NOT MOLES of molecules). The units are atomic mass units (amu).

1amu =1.660 538 782×10–27 kg                1 amu is 1/12 the mass of a carbon-12 atom which has a mass of 12.0000.

 

Reading Simple Chemical Formulas- Each element begins with a CAPITAL letter. The subscript belongs to the element it follows and indicates how many of that atom there are. If there is only 1 atom we do not use subscripts.

H2O      2 hydrogen    1 oxygen

Reading Compounds that have (parenthesis's).

When there is parenthesis's around a group of atoms we must multiply each atom by the subscript to get the total number of each element.

Ca(NO3)2     1 Calcium  2 Nitrogen and 6 Oxygen -->  3 x 2

 

How do we determine molar mass?

The molar mass is calculated by taking the sum of the atomic weights of all the atoms which form the molecule.

First determine the number of each atom in the formula.

1. Water is made up of 2 hydrogens and 1 oxygen.

Find the molar mass.

2. Multiply the number of each atom by its atomic weight (found on the Periodic Table of the Elements). 

            H2   

H     2  x 1.00794   =2.01588Add them up  Molecular Weight=18.01528g/mol  

For our class we can round to 1 decimal place so 18.0g/mol

O     1  x 15.9994 = 15.9994

          C6H12O6

C     6    x  12.0107=  72.0642Add them up  Molecular Weight=180.15588g/mol  

rounded to 180.2g/mol

H     12  x  1.00794=  12.09528
O     6    x  15.9994=  95.9964

        Ca(NO3)

Ca    1   x   40.078   =  40.078Add them up  Molecular Weight=164.0878g/mol  

rounds to 164.1g/mol

N     2   x   14.0067 =  28.0134
O     6   x  15.9994  =  95.9964

         

Highlight box to reveal the molar masses
FormulasHighlight to Reveal Molar Masses (g/mol)
CO244
HNO363
CCl4182
Na2SO4142
C12H22O11342
NH4OH35
Cu(NO3)2125
MgBr2184
CH3COOH60
Be(OH)243
LiBr87
CaBr2200
KNO3101
KF58
Na2CO3106
Ca(OH)274.1
CuSO4159.6
C3H4O388.0

Mole Conversions

Chemical Demonstration Videos