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how to apply mole concept in problems ?
All calculations in chemistry are based on the smallest unit of any compound or element called a mole. A mole is a very important unit for a chemist. Chemical equations, when written in the form of chemical reactions, give us the moles of the compounds or entities reacting and moles of products formed.

Thus, it is essential to understand all about moles. Since moles are nonconvertible to mass and vice versa, it is a very important tool in stoichiometry calculations and in balancing chemical reactions.
Mole concept can be applied even to an ionic compound. One mole of an ionic compound represents one mole (6.023 x 1023) formula units of that compound.

Mole Concept and Stoichiometry
Calculation of the mass of an atom of an element
= Gram atomic mass / Avogadro number
Calculation of the mass of one molecule of a substance:
= Gram molecular mass / Avogadro number
Calculation of the number of atoms in a given mass of an element:
= Mass of element in grams / gram atomic mass x N0
Number of molecules in a given mass of the substance
= Mass of substance in grams / gram molecular mass x N0
Calculation of the number of molecules present in V liters of gas at S.T.P
= Volume of the gas in liters / 22.4 liters x N0

Example:
Calculate the number of moles in 25 g of Calcium Carbonate.

Solution:
Molecular mass of CaCO3 = 100
Number of moles of Calcium Carbonate
= Mass of Calcium carbonate in grams/Molar mass of calcium carbonate
= 25 g / 100 g.mol-1 = 0.25 mole of calcium carbonate.


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