CBSE Class 11-science Answered

Mole Concept

A mole is a collection of 6.022 × 10²³ particles.

A mole is defined as the amount of a substance containing elementary particles like atoms, molecules or ions in 12 gram of carbon-12 (¹²C).

Avogadro’s number

It is defined as the number of atoms present in 12 gram of C-12 isotope, i.e. 6·023 × 1023 atoms. It is denoted by NA or L.

     NA                       = 6·023 × 1023

 1 mole of atoms               = 6·023 × 1023 atoms

1 mole of molecules               = 6·023 × 1023 molecules

1 mole of electrons             = 6·023 × 1023 electrons

1 mole of a gas             = 22·4 litre at S.T.P.

Molarity tells us the number of moles of solute in exactly one liter of a solution. (Note that molarity is spelled with an "r" and is represented by a capital M.)

We need two pieces of information to calculate the molarity of a solute in a solution:

• The moles of solute present in the solution.
• The volume of solution (in liters) containing the solute.

To calculate molarity we use the equation: