Chemistry

# Mole (chemist secret unit): Definition, Examples and calculation Formula

A mole is defined as the amount (mass) of a substance that contains 6.02 x 1023  number of particles ( atoms, molecules or formula units). It establishes a link between  mass of a substance and number of particles as shown in summary of molar calculations. It is abriviated as ‘ mole’ .

You know that a substance may be an element or compound ( molecular or ionic). Mass of the substance is eather one of the following: atomic mass, molecular mass or formula mass. These masses are expressed in atomic mass unit (amu). But when these masses are expressed in grams, they are called as molar masses.

Scientists have agreed that Avogadro’s number of particles are present in one molar mass of a substance. Thus, quantitative definition of mole  is the atomic mass, molecular mass or formula mass of a substance expressed in grams is called mole.

For example:

Atomic mass of carbon expressed as 12g = 1 mole of carbon

Molecular mass of H2O expressed as 18g = 1 mole of water

Molecular mass of H2SO4 expressed as 98g = 1 mole of H2SO4

Formula mass of NaCl expressed as 58.5 g = 1 mole of NaCl

Thus,  the relation between mole and mass can be expressed as:

A detailed relationship between a substance and a mole through molar mass and number of particles is present here.

Summary showing a relationship between a substance and a mole.

### Example for calculation of Moles:

Calculate the gram molecule (number of moles) in 40 g of H3PO4.

Solution:

Given mass of H3PO= 40 g

Molecular mass of H3PO4 = 98 gmol-1

Putting these values in equation

Therefore, 40 grams will contain 0.408 gram molecule (mol) of H3PO4 .

### One Comment

1. atwoodsports says:

Pl can you explain history why mole is secrete unit in chemistry…

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