Mole Concept - Class Notes

Question 1 Define a mole?

Question 2 What is the value of Avogadro’s constant?

Question 3 Define mole of an atom?

Question 4 Define mole of a molecule?

Question 5 Write the formula to calculate the number of moles?

Mole Concept

In a chemical reaction equation,it is more convenient to use quantity of substance in number of its molecules or atoms rather than their masses,so we use a new unit called MOLE.

If we weigh an element equal to its atomic mass in grams,then it contains 6.022×10²³ atoms of the element.The gram atomic mass of the element as well as 6.022×10²³ atoms of the element, both represent 1 mole of element.1 mole of any species (atoms,molecules,ions) is equal to its atomic mass or molecular mass in grams.

No. of particles(atoms, molecules, ions) in 1 mole=6.022×10²³

This number is called as AVOGADRO’S CONSTANT

1 mole of atom=6.022×10²³atoms

1 mole of molecules=6.022×10²³molecules

Mole of atoms

1 mole of atoms of an element has a mass equal to the gram atomic mass of the element.

For Ex: 1 mole of oxygen atoms=16 grams

The symbol of an element represents 1 mole of atoms of that element.

o represents 1 mole of oxygen atoms.

2 o represents 2 moles of oxygen atoms.

Mole of Molecule

1 mole of molecules of a substance has a mass equal to the gram molecular mass of the substance.

For Ex:The gram molecular mass of oxygen is 32 grams.‎O₂ represents 1 mole of oxygen molecule

2 ‎‎O₂ represents 2 mole of oxygen molecule

1 mole of sulphuric acid,_, H₂SO₄ contains 2 moles of hydrogen atom,1 mole of sulphur atom,4 moles of oxygen atoms.

1 mole of H atom=1u=1g=6.022×10²³ H atoms
1 mole of molecule=2u=2g=6.022×10²³ molecule
1 mole of water molecule=18u=18g=6.022×10²³ water molecule
1 mole of sodium atom=23u=23g=6.022×10²³ sodium atom

Mole represents:

1) 6.022×10²³ atoms,molecules or ions of a substance.
2)The amount of a substance equal to its gram atomic mass or molecular mass.
3)A definite number of atoms,molecules or ions of a substance.