Mass of 1 Mole of atom is called Molar Mass

 

How is Molar Mass Calculated?

The molar mass of a substance is equal to the atomic mass of a substance taken in grams .

Molar mass is the mass of 1 mole of a substance .

It is denoted by the letter M .

 

Let us calculate the Molar Mass of Calcium Carbonate (CaCO 3 )

Molar Mass-Teachoo-01.jpg

What is a Molecule?

A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule

 

1 molecule of CaCO 3 consists of : 1 Calcium (Ca) atom

                                                        1 Carbon (C ) atom

                                                       3 Oxygen (O) atoms

 

M of CaCO 3 = (1 x mass of Ca) + (1 x mass of C) + (3 x mass of O)

M of CaCO 3 = (1 x 40) + (1 x 12) + (3 x 16)

M of CaCO 3 = (1 x 40) + (1 x 12) + (3 x 16)

M of CaCO 3 = 100g/mol

 

Example 1

Atomic Mass of hydrogen = 1 u

Hence, Gram Atomic Mass = 1 gram

It means that Mass of 1 mole of Hydrogen = 1 gram

Since 1 MOLE = 6.022 x 10 23  atoms

We can say that

Mass of  6.022 x 10 23  atoms of Hydrogen = 1 gram/mole

 

What is a Molecule?

A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule

 

Example 2

Atomic Mass of oxygen atom = 16 u

Hence, Gram Atomic Mass = 16 gram

 

It means that Mass of 1 mole of Oxygen = 16 grams

Since 1 MOLE = 6.022 x 10 23  atoms

We can say that

Mass of  6.022 x 10 23  atoms of Oxygen = 16 grams/mole



Some formulae related to mole

1 mole of an atom = 6.022 x 10 23 atoms = molar mass of that atom

That is,

1 mole of C (Carbon) = 6.022 x 10 23 atoms of C (Carbon) = 12g of Carbon

 

 

What is a Molecule?

A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule

 

Sometimes we're given the values of 2 things and are supposed to find the value of the third.

 

So, we should remember that,

FORMULA 1 - Number of moles of a substance = Given mass of the substance / Molar mass of the substance

= m/M

Q     Find number of moles of H 2 in 10g of H 2

Ans  Given mass of H 2 = m =10g

        Molar Mass of H 2 = M=  2g/mol

        We know that,

        Number of moles of a substance = Given mass of the substance / Molar mass of the substance

= m/M

= 10g / 2g mol -1

= 5 moles

 

 

What is a Molecule?

A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule

 

  1.         How many moles are there in 52g of Helium?

We know that

            Atomic Mass of Helium = 4 u

            So Molar Mass of  Helium = 4 g mol -1

It means that Mass of 1 mole of Helium = 4 grams

We can also write as

= m/M

= 52/4

=13

So, 13 moles are there in 52g of Helium

 

FORMULA 2 - Number of moles of a substance = Number of particles of the substance / Avogadro's Constant

        = Number of particles / 6.022 x 10 23

        = N/N O

  1. How many moles is 12.044 x 10 23 atoms of He?

A Number of atoms of the He = N = 12.044 x 10 23

 

 

What is a Molecule?

A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule

 

Avogadro's Constant = N O = 6.022 x 10 23

We know that,

            Number of moles of a substance = Number of particles of the substance / Avogadro's Constant

= N/N O

= 11.044 x 10 23 / 6.022 x 10 23

=  2 moles of He atoms

Note - We usually denote number of moles by 'n'

 

So, this brings us to the 3rd formula;

FORMULA 3 -  Given mass of the substance / Molar mass of the substance = Number of particles of the substance / Avogadro's Constant

=> m/M = N/N O

 

Example - 3.3, 3.4

In text Question -

NCERT Question -7,8,9,10,11

 

What is a Molecule?

A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule

  1. Class 9
  2. Chapter 3 Class 9 - Atoms And Molecules (Term 2)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo