Molar Mass Calculation

Molar Mass

Since the particles are a group of atoms chemically joined together the final mass for these molecules known from the masses of their atoms i.e., we use relative mass to compare various molecules in terms of mass. Meaning that:-

Molar mass of matter =Total relativistic masses of atoms which make up matter

Molar mass is the mass of 1 mole of a compound in gram unit. (Molar mass used to be called as molecular mass formerly.)

For example, if we want to calculate the molar mass of methane gas (CH₄) or if we ask what is the mass of 1 mole of methane gas, as each methane molecule has 1 C and 4 H atoms, 1 mole of methane molecule contains 1 mole of C atom and 4 moles of H atoms. According to this, we can calculate the mass of 1 mole of methane gas as follows:

·       Mass of 1 mole of C = 1 × 12 = 12 g/mol

·       Mass of 4 moles of H = 4 × 1= 4 g/mol

·       Mass of 1 mole of CH₄ = 16 g/mol

In the same manner, we can calculate molar mass of H2SO4 acid.

·       Mass of 2 moles of H = 2 × 1= 2 g/mol

·       Mass of 1 mole of S = 1 × 32 = 32 g/mol

·       Mass of 4 moles of O = 4 × 16 = 64 g/mol

·       Mass of 1 mole of H2SO4= 98 g/mol

If 16g of methane gas makes up 1 mole of CH4 and 98 g of sulfuric acid makes up 1 mole of H₂SO₄, logically we can call those masses as molar mass. As we understand from previous calculations we have made, in chemistry, all atoms and molecules are bound with the following:

1.      Atomic mass and molar mass

2.     Mole

3.     Avogadro’s number

Avogadro’s number or Avogadro’s constant is the number of atoms in 1 mole of an element or number of molecules in 1 mole of a molecule. It is shown with NA. Previously, we have mentioned that atoms, molecules or ions as many as Avogadro’s number are called as a mole.

Example 1

Find the molar mass for the following compounds:

a. Aqueous sodium sulfate Na2SO4.7H2O

b. Juglone C10H6O3

c. Sulfur dioxide SO2

Solution:

Example 2

Find out the mole numbers of the following compounds.

a)9.6 g of SO2

b) 85 g of NH3

Solution:

a) Molar mass of SO2:

b) Molar mass of NH3:

Example 3

Calculate the mass of 0.7 mol of manganese dioxide (MnO2).

Solution: