# Molar Mass, Worked Examples and Differences with Molecular Mass

### What is Molar Mass?

Molar mass is the Mass of one mole of a substance expressed in grams per mole (g/mol).

For instance, since one mole of oxygen atom (O) has a mass of 15.9994 gram, its molar mass would therefore be 15.9994g/mol.

The formulas below will prove useful in chemical calculations involving mole, mass and molar mass respectively.

Mole = Mass/Molar Mass

Mass = Mole x Molar Mass

Molar Mass = Mass/Mole

### Worked Examples on Molar Mass

##### Example 1

• Calculate the molar mass of 2 moles of Ethanol (2C2H5OH). (Carbon = 12, Oxygen = 16 and Hydrogen = 1)

Notice the 2 in front of ethanol's chemical formula. It stands for the number of moles; (that is; 2 moles in this case). If no value is present, then then it's regarded as 1 mole.

Two moles of Ethanol are composed of 4 atoms of carbon; 10 atoms of hydrogen and 2 atoms of oxygen. (We got the values by multiplying the atoms of each element by the “2” in front of the compound).

(12 x 4) + (1 x 10) + (16 x 2)

48 + 10 + 32

Molar Mass of 2 moles of Ethanol = 90g/mol

##### Example 2

• Calculate the molar mass of Sodiumtrioxocarbonate(IV). (Na2CO3) (Sodium=23, Carbon=12, Oxygen=16)

Na2CO3 is composed of 2 atoms of sodium, 1 atom of carbon and 3 atoms of oxygen.

(23 x 2) + 12 + (3 x 16)

46 + 12 + 48

##### Example 3

• Calculate the molar mass of Ca3(PO4)2. (Calcium=40.078 , Phosphorus=30.973762 and Oxygen=15.999)

Ca3(PO4)2 is composed of 3 atoms of calcium, 2 atoms of phosphorus and 8 atoms of oxygen

Note: The subscript 2 applies to only (PO4). We therefore multiplied potassium (P) by 2 and the O4 by 2.

(40.078 x 3) + (30.973762 x 2) + (15.999 x 3)

120.234 + 61.947524 + 47.997

### Differences between Molecular Mass and Molar Mass

Molecular Mass refers to mass of a molecule in relation to carbon-12.

Molar Mass refers to the mass of one mole of a substance.

Molecular Mass is measured in Atomic Mass Unit (AMU) or Dalton (Da).

Molar Mass is measured in grams per mole (g/mol).

The Molecular Mass of a molecule is derived by calculating the sum of the atomic mass of each atom present in the molecule.

The Molar Mass is derived by dividing the mass of the substance by the number of moles in that substance.

Note: The values of molecular mass and molar mass are always the same, except that they have different Standard International Units S.I Units.