what is mole in chemistry?

What is a Mole in Chemistry?

The mole concept and stoichiometry are one of the many topics students usually encounter first while learning chemistry and there is a need to patiently introduce this to students.

What is a Mole in Chemistry? Mole is a term that has been well misconstrued by a lot of learners but sincerely it shouldn’t be so.

Before I go into detail in explaining this, I want to give few examples of what a mole of elements really implies.

When you have a bunch of keys, a school of fish, a team of players, and so on ….the same goes for a mole of elements or a mole of an atom of an element.

Mole Chemistry is simply a concept that talks about the application of mole in solving stoichiometry calculations.

What is the Definition of a Mole?

A mole is the amount that contains many elementary particles are there are 12 grams in carbon 12.

Hold on, no need to be confused that 12 grams of carbon have many elementary particles of carbon?

A glance at the periodic table gives us some more clarity on the atomic mass of elements.

To understand this better, just recall that the atomic mass of carbon is 12 but you can confirm this from the table. it means that I mole of carbon contains the atomic mass of carbon.

Carbon is arbitrarily used here as the reference for us to note that 1 mole of an element contains the atomic mass of the element.

How big is the Mole?

This question is raised because we humans use weight and mass and we want to relate the mole to these.

Actually, a mole is neither a unit of weight nor a unit of mass.

1000 moles of any substance will have the same number of elementary particles; we use both grams and moles in chemistry. A mole is simply a “building block” used to describe very large or small numbers. One gram is equal to one mole.

However, a mole of a substance can be related to mass, particles {Avogadro’s number} and even volume.

let me say this, a mole does not have a specific weight but depends on the substance of reference.

Mole and Mass Relationship

One mole of an atom of an element = atomic mass of the atom of an element

One mole of a molecule = molecular mass of the molecule

Mole and Avogadro’s number relationship

One mole of a substance – Avogadro’s number

Note =Avogadro’s number = 6.02 X 1023 atoms

This value 6.0 x 1023 is equally called the Avogadro’s constant.

Mole and volume relationship

One mole of a gas = molar volume

Molar volume is the volume of one mole of a gas at STP.

Note molar volume =22.4 dm23

The Mole concept

People also do ask questions like how many grams are in one mole of water or how many moles are in 1 liter of a substance.

The various questions can only be solved using the mole concept, the mole concept provides a simple way of solving calculations involving mole.

I will talk about the whole mole concept in future articles.

The mole concept is the foundation stone of chemistry since it helps to make calculations relating to the number of substances involved in any reaction. One mole of any substance has 6.0 x 1023 molecules or atoms or elementary particles in it.

learning to do some simple tasks involving mole chemiatry would be great as we have littered in all olevel chemistry calculations involving mole in Chemistry

10 Mole Concept Calculations

Example 1

What is the mass of 2.2 moles of Carbon?



1 dozen of eggs = 12,…it is constant

so also

1 mole of carbon = 12g  {from periodic table}

Example 2

How many grams of water are there in 3 moles of water?


Recall that

1 mole of a molecule = molecular mass/ molar mass

1 mole of water = molar  mass of water

To get the atomic mass of element, use periodic table

So from periodic table, H =1, O=16

Molar mass of Water H2O = 1 X2 +16 = 18g/mol

Therefore   1 mole of water = 18g

                   3 moles = 3 x 18 = 54g

Example 3

How many moles are there in 200 of Calcium trioxo carbonate IV {CaCO3}


we use equivalence calculation that we have been using for the other ones

1 mole of CaCO3 = 100g


From periodic table Ca =40, C=12, O-16

CaCO3= 40+12+16x 3= 40+12+48= 100g

Therefore 1 mole of CaCO3 = 100g

                                x moles =  200g

 x moles = 1 mole x 200g / 100g  = 2 moles

Example 4

What is the volume of 3.5 moles of carbon IV oxide?


Recall that 1 mole of a gas = molar volume

So 1 mole of CO2 = Molar volume

1 mole of CO2 = 22.4 dm3

3.5 moles of CO2 = x

x = 3.5 X 22.4 =78.4 dm3

Example 5

How many particles are there in 0.5 moles of sodium?


1 mole of Na = 6.02 x 10 >23 atoms

0.5 moles of Na  = x

x = 0.5 x 6.02 x 1023/1 = 3.01 x 1023 atoms

Example 6

How many atoms are there in 20g of Calcium?


1 mole of Ca = 40g = 6.02 x 1023 atoms

                         20g = x

  x = 20g x 6.02 x 1023/ 40g

  x = 3.01 x 1023 atoms

Example 7

Consider this equation, N2 + 3H2 à  2NH3

How many moles of ammonia would be produced by 4 moles of hydrogen combining with nitrogen?


Background statement from the balanced equation

3 moles of Hydrogen yield 2 moles of ammonia

There 4 moles of hydrogen yields ……..

By equivalence calculations

      If 3 moles of H2 = 2 moles of NH3

Then 4 moles of H2 = x

X = 4 x 2 /3   = 2.67 moles of NH3

Example 8

Consider the equation shown below;

CH4 + 2O2  –> CO2 + 2H2O

If 3.3 moles of methane burns completely in oxygen, Calculate the volume of carbon iv oxide evolved.


From balanced equation

Background statements

1 mole of CH4 = 1 mole of CO2

3.3 moles of CH4 = X

X = 3.3 X1 /1 = 3.3 moles of CO2

But the examiner asked for the volume of CO2?

Convert the mole to volume

I mole of CO2 = 22.4 dm3

3.3 moles of CO2 = x

X = 3.3 x 22.4dm3

X =73.92dm3

Example 9

What mass of Magnesium chloride would be produced by the reaction of 4.2 moles of magnesium with hydrochloric acid?

Mg + 2HCl  –> MgCl2 + H2


Background statement from the balanced equation

1 mole of Mg =1 mole of MgCl2

4.2 moles of Mg à x

X = 4.2 x1 /1 = 4.2 moles of MgCl2

But we are asked for the mass of MgCl2?

So convert mole to mass

I mole of MgCl2 = 95g

4.2 moles of MgCl2 = x

X = 4.2 x 95 = 399g of MgCl2

Example 10

Consider the equation; 2SO2 + O2 à 2SO2

How many moles of sulfur iv oxide will produce 4 moles of sulfur vi oxide?


Background statement from the balanced equation

2 moles of SO2   = 2 moles of SO3

x moles               = 4 moles

x = 2 x 4 /2 = 4 moles of SO2

So I believe we have been able to answer the question of what is a mole in Chemistry. However, the mole concept leads straight to the stoichiometry calculations.

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