CBSE Class 11-science Answered

Mole Concept

• We know that a dozen is a collection of 12 substances, a century is a collection of 100 substances and a gross is a collection of 144 substances.
• We use the terms dozen, century, gross etc. to express a certain quantity of a substance.
• Similarly, a mole is a word used to describe a collection of particles i.e. atoms, molecules or ions.

Avogadro experimentally found that one mole of any substance always contained 6.022 × 1023particles.

This number is called the Avogadro’s number, denoted by N0.

Important Formulae and Hints to Solve the Questions Related to Mole Concept

The relationship between Mole, Avagadro number and Mass

One Mole = 6.022 X 1023 (Avogadro's No.) atoms/ions/molecules/particles

No. of moles = Mass/Molecular weight

No. of atoms = Number of moles (Given mass / Molar mass ) x Avogadro number

Let us take an example of 2gm of hydrogen.

No. Of moles of hydrogen molecule=2(wt.)/2(Mol. wt)  

=1 mole of hydrogen molecules  

=6.022 X 1023  molecules of hydrogen