Pg:- 99,100,101,102

Ch:- 5

The mole is a fundamental concept in chemistry used to measure the amount of a substance. It provides a bridge between the atomic/molecular scale and the macroscopic scale, allowing chemists to count particles (atoms, molecules, ions, etc.) in practical amounts of material.

Definition

1. Scientific Definition:

   • A mole is the amount of substance that contains as many particles (atoms, molecules, or ions) as there are atoms in 12 grams of carbon-12.

   • This number is known as Avogadro’s number (NA​): NA=6.022×10^23 particles/mol

2. Practical Understanding:

   • One mole of any substance contains 6.022×10^23 entities:

     • 1 mole of hydrogen atoms contains 6.022×10^23 atoms.

     • 1 mole of water molecules (H2O contains 6.022×10^23 water molecules.

Relation to Mass

• The mass of one mole of a substance (in grams) is numerically equal to its relative atomic mass or relative molecular mass.

  • Example:

    • H2​: Relative molecular mass = 2.0 → 1 mole = 2.0 grams.

    • CO22​: Relative molecular mass = 44.0 → 1 mole = 44.0 grams.

Key Units

• Molar Mass (g/mol): The mass of one mole of a substance.

• Number of Particles: N= n × NA where:

  • N: Number of particles

  • n: Number of moles

  • NA​: Avogadro’s number

Applications

1. Chemical Calculations:

   • Used to determine the amounts of reactants and products in chemical reactions.

2. Stoichiometry:

   • Helps relate masses, volumes, and numbers of particles in a reaction.

3. Concentration:

   • Moles are used to define the concentration of solutions (mol/L).

   
   

Examples

1. Moles in Elements:

   • 1 mole of Na weighs 22.99 g and contains 6.022×10^23 atoms.

2. Moles in Compounds:

   • 1 mole of H2O weighs 18.02 g and contains 6.022×10^23 molecules.

3. Volume of Gases:

   • At standard temperature and pressure (STP), 1 mole of any ideal gas occupies 22.4 liters.