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.
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 | |||
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How many gms of element 'Sodium' must be taken to get 1 mol of the element 'Sodium' ? | |||
Right Option : C | |||
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________________________ named in the honour of Italian scientist Amedeo Avogadro. | |||
Right Option : D | |||
View Explanation |
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