Mole Concept: Introduction, Origin and Formulae Calculation

Can you count a dozen or a gross? If you answer yes, have you ever wondered about counting the number of particles in a given matter? This article will teach you about a concept that makes counting particles such as atoms or molecules more effortless, and that concept is known as Mole Concept.

The mole concept is a convenient method of expressing the amount of a substance. Even one gram of a pure element is known to contain a large number of atoms when dealing with particles at the atomic (or molecular) level. The mole concept is commonly applied in this context. It is primarily concerned with the ‘mole,’ which is a count of a vast number of particles. Continue reading to know more.

What is Mole Concept?

The magnitude of an atom is very small, and it is not easily countable. Different kinds of atoms or ions do not alone define the uniqueness of substances, but it depends on the number of ions or atoms. For example, carbon dioxide \({\rm{C}}{{\rm{O}}_{\rm{2}}}\) and carbon monoxide \({\rm{CO}}\) are identical because their molecule consists of similar atoms- carbon and oxygen.

However, the number of combined atoms is different in both substances. Due to this, the substance exhibits different properties. Hence, the requirement of establishing a new unit for measurement of the quantity of the substance.

When dealing with particles of an atom or a molecule, even a small quantifiable amount contains many atoms, or molecules, or ions. For this purpose, the mole concept plays an essential role in chemistry.

Why is the Mole Concept Needed?

We need the mole concept to bridge the gap between the microscopic world of atoms and human’s macroscopic world. The particles at the molecular level are invisible to us. Because of this, we can’t count or weigh these individual particles on a scale.

What is a Mole?

Mole is the amount of substance in a chemical system that contains as many elementary entities (electrons, atoms, molecules, ions, or formula units) as there are atoms in exactly \(12\) grams of the carbon\(-12\) isotope.

It is an experimental observation that there are \(6.022 \times {10^{23}}\) \({\text{C}}\) atoms in \(12\) grams of carbon. Thus, one mole of carbon contains \(6.022 \times {10^{23}}\) \({\text{C}}\) atoms and the mass of one mole of carbon is equal to \(12\) grams which is its gram atomic mass.

\(1\) mole\( = 6.022 \times {10^{23}}\) particles of matter of any chemical substance.
This number is quite huge and has a special name called the Avogadro’s number or Avogadro’s constant in honour of the Italian mathematician who contributed to our understanding of the mole concept

Similarity Between a Dozen and a Mole

One mole may represent \( = 6.022 \times {10^{23}}\) molecules or \( = 6.022 \times {10^{23}}\) atoms or \( = 6.022 \times {10^{23}}\) electrons. This relation of a mole is similar to the use of \(1\) dozen used to represent \(12\) quantities of anything.

Origin of the term ‘Mole’

Mole is a Latin word that means ‘heap’ or ‘pile’. Scientist Wilhelm Ostwald used the term mole in \(1896\) to represent a collection of a large number of particles (atoms and molecules) of a chemical substance. It got accepted as a unit of quantity in \(1967\).

Atomic Mass

Atomic mass is the mass of an atom expressed in atomic mass units or amu. One atomic mass unit is equal to one-twelfth of the mass of an atom of carbon \(12\) isotope.

Molecular Mass

The molecular mass of a substance is the number of times the molecule of the substance is heavier than one-twelfth the mass of an atom of carbon \(-12\).
Or, the molecular mass is equal to the sum of the atomic masses of all the atoms present in one molecule of a substance. 

Gram Atomic/Molecular mass

The atomic masses of elements expressed in grams are their gram atomic masses. For example, the atomic mass of oxygen is \(16\) amu. Therefore, the gram atomic mass of oxygen \({\rm{ = 16}}\,{\rm{g}}\).

The atomic masses of molecules expressed in grams is their gram molecular mass. For example, The molecular mass of water is \(18\) amu. Therefore, the gram molecular mass of water \({\rm{ = 18}}\,{\rm{g}}\).

Molar Mass

The Molar Mass of Atoms – The mass of one mole of atoms is called its molar mass. That is, the molar mass of atoms is equal to the mass of  \( = 6.022 \times {10^{23}}\) atoms. The value of molar mass is expressed as grams per mole, written as \({\rm{g/mol}}\) or \({\rm{g}}\,{\rm{mo}}{{\rm{l}}^{ – 1}}\). 

For an atom, the numerical value of each one of atomic mass, relative atomic mass, gram atomic mass and molar mass is the same. For example,

1. The atomic mass of hydrogen is \(1\,{\rm{u}}\).
2. The relative atomic mass of hydrogen is \(1\).
3. The gram atomic mass of hydrogen is \(1\,{\rm{g}}\).
4. The molar mass of a hydrogen atom is \({\rm{1}}\,{\rm{g}}\,{\rm{mo}}{{\rm{l}}^{ – 1}}\).

The Molar Mass of some atoms

The Molar Mass of Molecules – The mass of one mole of a molecule is called its molar mass. That is, the molar mass of molecules is equal to the mass of \( = 6.022 \times {10^{23}}\) molecules. The value of molar mass is expressed as grams per mole, written as \({\rm{g/mol}}\) or \({\rm{g}}\,{\rm{mo}}{{\rm{l}}^{ – 1}}\). 

For a molecule, the numerical value of each molecular mass, relative molecular mass, gram molecular mass and molar mass is the same.

For example,

1. The molecular mass of oxygen is \({\rm{32}}\,{\rm{u}}\).
2. The relative molecular mass of oxygen is \(32\).
3. The gram molecular mass of oxygen is \({\rm{32}}\,{\rm{g}}\).
4. The molar mass of the oxygen molecule is \({\rm{32}}\,{\rm{g}}\,{\rm{mo}}{{\rm{l}}^{ – 1}}\)

The Molar Mass of some molecules are:

Mole and its Role in Chemical Equations

We shall discuss the role of the mole in terms of the following type of relations useful for chemical equations:

1. Relation between mass and mole
2. Relation between mass, number of atoms or molecules.
3. Relation between a mole, number of particles and mass.

The understanding of the relations become easier when symbols and terms are familiar. Therefore, some of the symbols and terms related are as follows:

\({\rm{m = }}\) mass of the substance

\({\rm{M = }}\) molar mass of the substance

\({\rm{n = }}\) number of moles

\({\rm{N = }}\) number of particles of the substance

\({{\rm{N}}_{\rm{A}}}{\rm{ = }}\) Avogadro’s constant \( = \) Avogadro’s number \( = 6.022 \times {10^{23}}\)

Formulae used for the Calculations – Here we will see how we can use Molar Concept for different calculations.

1. For calculation of the number of moles from mass:

Number of moles \( = \frac{{{\rm{ Given mass of the substance }}}}{{{\rm{ Molar mass of the substance }}}}\)
Or, \({\text{n=}}\frac{{\text{m}}}{{\text{M}}}\)

2. For calculation of mass from the number of moles-

Mass \({\rm{ = }}\) Number of moles \( \times \) Molar mass
Or, \({\rm{m = n \times M}}\)

3. For calculation of the number of particles (atoms or molecules) from the mass:

Number of particles \( = \frac{{{\rm{ Given mass of the substance }}}}{{{\rm{ Molar mass of the substance }}}} \times \) Avogadro constant
Or, \({\rm{N}} = \frac{{\rm{m}}}{{\rm{M}}} \times {{\rm{N}}_{\rm{A}}}\)

4. Calculation of mass from the number of particles (atoms and molecules)

Mass \({\rm{ = }}\) Mole \( \times \) Molar Mass
Or, \({\rm{m = }}\frac{{\rm{N}}}{{{{\rm{N}}_{\rm{A}}}}}{\rm{ \times M}}\)

Summary

When dealing with particles of an atom or a molecule, even a small quantifiable amount contains many atoms, or molecules, or ions. For this purpose, the mole concept plays an essential role in chemistry. This article teaches how an atom or a molecule can be calculated using the mole concept. Also, we learned about the term mole and Avogadro’s number and the relation between the mole, the number of particles, and the mass of the substance.

FAQs

Q.1. Define Avogadro’s number?
Ans: \(1\) mole\( = 6.022 \times {10^{23}}\) particles of matter of any chemical substance.
This number has a special name called the Avogadro’s number or Avogadro’s constant in honour of the Italian mathematician who contributed to our understanding of the mole concept.

Q.2. What is the importance of the mole concept?
Ans: Atoms and molecules are very small, and the mole concept allows us to calculate the number of atoms and molecules. It also establishes a standard for reaction stoichiometry. 

Q.3. What are the advantages of the mole concept?
Ans: With the knowledge of the mole concept and its relation to the mass of the chemical substance, it has become convenient to collect any number of atoms and molecules without counting them.

Q.4. Define mole.
Ans: Mole is the amount of substance in a chemical system that contains as many elementary entities (electrons, atoms, molecules, ions, or formula units) as there are atoms in exactly \(12\) grams of the carbon\(-12\) isotope.

It is an experimental observation that there are \( = 6.022 \times {10^{23}}\) \({\text{C}}\) atoms in \(12\) grams of carbon. Thus, one mole of carbon contains \( = 6.022 \times {10^{23}}\) \({\text{C}}\) atoms, and the mass of one mole of carbon is equal to \(12\) grams which is its gram atomic mass.

Q.5. How many particles (atoms, molecules, or ions) are there in \(1\) mole of a chemical substance? 
Ans: There are \( = 6.022 \times {10^{23}}\) particles of matter of any chemical substance in one mole.

Q.6. How is the mole related to the dozen?
Ans: One mole may represent ( = 6.022 times {10^{23}}) molecules or ( = 6.022 times {10^{23}}) atoms or ( = 6.022 times {10^{23}}) electrons. This relation of a mole is similar to the use of (1) dozen used to represent (12) quantities of anything.

We hope this detailed article on the Mole Concept is helpful to you. If you have any questions about this article or, in general, about the Mole concept, ping us through the comments section, and we will get back to you.