Question

Explain with examples what is meant by a "mole" of a substance.

Answer 1

It is a unit of an International system of units ie an SI system of units for calculating the amount of substance. And it is the simplest way by which we could represent a large number of atoms and molecules present in a compound.

Complete step-by-step answer: In the question, it is to explain briefly about a mole of a substance with example.
Before going into the system first we should know a few basic ideas.
We know that an atom is the simplest building block of a substance. Atoms combine to form the molecules and these add up in large numbers to form a substance.
So in a very small amount of substance, there will be a very large amount of atoms and molecules present and the representing the numbers of atoms and molecules and its calculations are very much hectic and confusing. And hence we use this mole concept to represent the amount of the substance in a much simpler way.
One mole of a substance simply means it contains Avogadro number of elementary entities like atoms, molecules, ions, etc.
Avogadro number has a value of$\text{6}\text{.022 }\\!\\!\times\\!\\!\text{ 1}{{\text{0}}^{\text{23}}}$, is also called as the Avogadro constant.
So one mole of substance will have $\text{6}\text{.022 }\\!\\!\times\\!\\!\text{ 1}{{\text{0}}^{\text{23}}}$atoms or that number of molecules etc.
And mole has a definition that for one mole of C-12, it will have a mass of 12grams and will contain $\text{6}\text{.022 }\\!\\!\times\\!\\!\text{ 1}{{\text{0}}^{\text{23}}}$carbon atoms.
Another definition is, the amount of substance in a mole is equal to the relative molecular mass of the substance obtained in grams.
Now let's see few examples:
For 1 mole of Na will have $\text{6}\text{.022 }\\!\\!\times\\!\\!\text{ 1}{{\text{0}}^{\text{23}}}$ Na atoms.
For 3 moles of K atoms, multiply the number of atoms in one mole with 3 i.e., $\text{3 }\\!\\!\times\\!\\!\text{ 6}\text{.022 }\\!\\!\times\\!\\!\text{ 1}{{\text{0}}^{\text{23}}}\text{=18}\text{.066 }\\!\\!\times\\!\\!\text{ 1}{{\text{0}}^{\text{23}}}\text{atoms}$

Note: If questions related to mole are given, like a weight of a substance is given and if we know the molecular mass of the substance then we could calculate the number of moles of the substance and we could calculate the number of atoms, molecules, or ions present in the substance.
The equation for calculating the number of moles of substances are as follows:
$\text{Number}\,\text{of}\,\text{moles=}\dfrac{\text{Given}\,\text{mass}}{\text{Molecular}\,\text{mass}}$