Class 11 Chemistry Chapter 1 Some Basic Concept of Chemistry | Class 9 Chapter 3 Atoms and Molecules
In this article we will talk about very important concept in chemistry “ Mole Concept ” and “Molar Mass”.
During any chemical reaction atoms and molecules rearrange themselves to form new compound. However, atoms and molecules are very small in size. Therefore, even in very small quantity of substance these appear in very large numbers. Also, it is difficult to specify number of atoms and molecules during a chemical reaction due to their occurrence in large numbers. To this problem, solution is to measure the macroscopic quantities like mass or volume. With help of mole concept we are able to determine number of entities i.e. number of atoms, molecules, particles, electrons or ions. And so unit to measure an amount of substance is called mole denoted by mol.
Mole
One mole is amount of substance that can be defined as
“amount of substance containing same number of entities as that in 12g of 12C isotope.”
Mass of atom can be determined using spectrometer. By using spectrometer atomic mass of carbon 12 isotope was found to be 1.992648 × 10-23g. Therefore, number of entities in 12g of Carbon 12 isotope will be
Number of entities = amount of substance / mass of individual entity
Number of entities = 12 / 1.992648 × 10-23g
Therefore, Number of entities = 6.0221367 × 1023
6.0221367 × 1023 specifies number of entities present in 1 mol. This quantity could be number of atoms or number of molecules or number of electrons or other particle. This number is known as Avogadro Constant. Denoted by NA. for example, 1 mol of hydrogen gas contains 6.0221367 × 1023 hydrogen atoms. 1 mol of water contains 6.0231367 × 1023 water molecules. In the same way sodium chloride contains 6.0221367 × 1023 formula units.
Molar mass
Mass of one mole of substance in grams is called molar mass.
This also means the mass of 6.0221367 × 1023 entities in substance is called molar mass. For example: molar mass of water = 18.02 g/mol. Moreover, molar mass in grams is numerically equal to atomic or molecular mass in ‘u’
Keywords: Mole, Formula units, Atoms, Molecules. Avogadro’s Constant, Molar mass, Spectrometer, Carbon 12 isotope.
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