The Mole Concept
The Mole Concept
Mole Concept:
Wilhelm Ostwald introduced the term ‘mole’ in 1896, which was accepted as unit to represent a large quantity of atoms in 1967. The mole is the amount of a substance which contains as many particles (atoms, ions, molecules, formula unit etc.) as in 12gm of C-12. Thus, one mole of any species is that quantity in number having a mass equal to its atomic or molecular mass in grams.
The number of particles present in 1 mole of any substance is same and fixed which is equal to . This is a constant, known as Avogadro constant or Avogadro number (
) named in the honour of Italian scientist Amedeo Avogadro. Thus, mole is also defined as number of particles equal to the Avogadro constant.
1 mole =particles.
Derivation:
We know that mass of 1 atom is measured in terms of united mass (u)
1u= g. So, 1g of the element contains
atoms of the element. It comes out to be approximately
atoms.
Illustration: How many gms of each of the following elements must be taken to get 1 mole of the element?
1. Sodium 2. Chlorine 3. Copper
Solution: The mass of 1 mole of an element is its atomic mass expressed in grams. Since the atomic masses of sodium, chlorine and copper are 23g, 35.5g and 63.5g respectively, we get
1. sodium =23g
2. chlorine = 35.5g
3. copper = 63.5g
Illustration: Calculate the number of moles in 5.75g of sodium. (Atomic mass of sodium = 23)
Solution: 1 mole of sodium atoms = gram atomic mass of sodium = 23g
23g of sodium = 1 mole of sodium.
=
The number of particles present in 1 mole of any substance is same and fixed which is equal to ___________________________. | |||
| Right Option : C | |||
| View Explanation | |||
How many gms of element 'Sodium' must be taken to get 1 mol of the element 'Sodium' ? | |||
| Right Option : C | |||
| View Explanation | |||
How many gms of element 'Copper' must be taken to get 1 mole of the element 'Copper' ? | |||
| Right Option : D | |||
| View Explanation | |||
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