Wednesday, August 28, 2013

Mole Concept

           Number of particles of the substance is related to the mass of the substance. Mole is a unit of measurement used in chemistry. A chemical mass unit is defined to be 6.023 × 1023. atoms , molecules , ions or some other units.For Example in chemical equation ,

                                           2H2 + O2 → 2H2O
                  The above equation implies that 2 mole of dihydrogen and one mole of dioxygen react to give 2 mole of water. The mole may also be used to express the number of atoms , ions, or some other substances. But the concentration of solution is commonly expressed by its molarity , defined as the number of moles of the dissolved substance per litre of solution.
                     The mole may be defined as the amount of the substance that contains as many specified elementary particles as the no.of atoms in 12g of carbon-12 isotope. (i.e ) one mole of an atom consists of Avogadro number of particles.

Example for mole substances :
A mole of oxygen atom contain 6.023 × 1023 oxygen atoms.
A mole of oxygen molecule contains 2 × 6.023 × 1023 oxygen.

Example for ionic substance :
A mole of Sodium carbonate ( Na2CO3 ) quantity containing 6.023 × 1023  , Na2CO3 units. Each formula units of sodium carbonate contains 2 × 6.023 × 1023,  Na +  ions and  1 × 6.023 ×1023  CO32-   ions.

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