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CBSE - IX - Chemistry - Atoms and Molecules

what is mole and avagadro numbers ........pls tell me

Asked by 8th January 2012, 5:29 PM
Answered by Expert


The mole is a unit of measurement used  to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities (e.g., atoms, molecules, ions, electrons) as there are atoms in 12 grams of pure carbon-12 (12C), the isotope of carbon with atomic weight 12. This corresponds to a value of 6.02214179(30)1023 elementary entities of the substance. It is one of the base units in the International System of Units, and has the unit symbol mol. The number of molecules in a mole (known as Avogadro's number) is defined so that the mass of one mole of a substance, expressed in grams, is exactly equal to the substance's mean molecular weight.

Avogadro constant (NA) is defined as the ratio of the number of constituent particles  N (usually atoms or molecules) in a sample to the amount of substance n (unit mole) through the relationship NA = N/n.  For example, the mean molecular weight of natural water is about 18.015, so one mole of water is about 18.015 grams. 

Answered by Expert 8th January 2012, 10:23 PM

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