All you should know about mole concepts – Detailed Explanation & Formulas

Overview

Mole concept is the most crucial topic that is asked in various competitive exams like NEET & JEE , including board exams. The mole concept is one of the most fundamental topics in chemistry. In this article, we will see all the related topics while covering every subtopic in a detailed manner. Those topics include a thorough understanding of atomic and mass numbers, quantities related to mole concept and their formulae and other important aspects about the mole concept. 

Table of contents

Overview

Mole concept – explanation

What is a mole?

Quantities related to mole concept and their formulaeAtomic and molecular massMolar massGram atomic mass and Gram molecular mass

Related formulae

Number of electrons in a mole of hydrogen molecule

Applications of mole

Interesting facts

FAQ

Mole concept – explanation

The mole concept is a convenient method that helps express the amount contained in a substance. All types of measurements can be broken down into two main parts; the numerical magnitude and the unit in which the magnitude is being expressed. 

For instance, if we measure the mass of a box as 5 kilograms, the ‘5’ is considered the magnitude while ‘kilograms’ is its unit. 

Furthermore, while dealing with atomic or molecular particles, even a gram of a pure element is highly capable of containing enormous amounts of atoms. Due to this reason, the mole concept is one of the only concepts that is being utilised vastly. Henceforth, the primary focus on the unit is defined to be the mole, which is nothing but a count of large amounts of particles.

What is a mole?

In JEE chemistry Syllabus, a mole can be described as the number of a substance capable of containing exactly 6.022*10²³ elementary entities of the provided substance. This number is very popularly known to be Avogadro’s constant, and it can be denoted by ”NA”. The elementary entities capable of representing moles are monatomic ions, polyatomic ions, atoms, molecules and other related particles, namely electrons. 

To provide an example, a pure carbon 12 sample (C – 12) will contain a mass of 12 grams and has a 6.022*10²³ (NA) number of C – 12 atoms. The following formula specifies the number of moles of a substance contained in a given pure sample,

n=NNA

where,

n is denoted as the number of moles of the substance (or elementary entity)

N is the total number of elementary entities in the sample

NA is the Avogadro’s constant

In 1896, a German chemist named Wilhelm Ostwald invented ‘mole’. It was derived from the Latin word moles, which means ‘pile’ or ‘heap’.

Commonly, the number of moles of a molecule need not always be equal to the number of moles of its constituent elements. For instance, a mole of water consists of the NA number of H₂O molecules. Moreover, each of the water molecules contains two hydrogen atoms and one oxygen atom. So, it indicates that one mole of H₂O has 2 moles of hydrogen and 1 mole of oxygen.

Quantities related to mole concept and their formulae

The following are some of the most relevant and fundamental topics related to the mole concept and its formulae.

Atomic and Molecular mass

The atomic mass is nothing but the mass of one atom of the element expressed in atomic mass units (AMU). It can be accounted for the abundance of several isotopes of the element and takes an average value to the mass of one atom of the element.

For example, carbon’s atomic mass is defined as 12.011 atomic mass units since carbon samples usually consist of 98.89 % of the carbon – 12 isotopes, 1.11 % of carbon -13, and negligible amounts of carbon – 14. However, the atomic masses of the isotopes mentioned above vary. 

We can say that the atomic mass of the carbon – 12 would be 12 atomic mass units. Likewise, for carbon – 13, the atomic mass would be 13 amu. The atomic mass of the element can be seen as equal to the sum of the atomic masses of all its constituent elements. This quantity can be seen represented in terms of atomic mass units. Hence, the molecular mass of the water is equivalent to the summation of the atomic masses of its constituent, which are hydrogen and oxygen. 

The atomic mass of hydrogen can be denoted as 1.00794 amu, whereas the atomic mass of oxygen would be 15.9994 amu. Due to the fact that the water molecules consist of 2 hydrogen atoms, the molecular mass of H₂O can be written as 18.0154 amu.

Molar mass

A substance’s molar mass can be determined as the total mass of one mole of the substance. This can be illustrated in grams per mole (g/mol). Furthermore, the SI unit of this quantity can be kg/mol. 

The below-mentioned formula is used to represent the molar mass,

Molar mass of a substance= Mass of the substance in gramsNumber of moles

To give an instance, the molar mass of water is approximately 18.015 g / mol, which is the mass of NA number of water molecules.

Gram atomic mass and Gram molecular mass

The gram atomic mass of an element is nothing but the mass of one mole of that particular element. Likewise, the gram molecular mass of the compound represents the mass of a single mole of a compound. Hence, the gram atomic mass of hydrogen can be approximately equal to 1.007g and the gram molecular mass of water is approximately 18.015g.

Related formulae

In order to calculate the number of moles in a given sample of an element or a compound, we should divide the total mass of the sample by the molar mass of the element. The below mentioned is the formula for the same,

Number of atoms or molecules= Mass of the sampleMolar mass

To calculate the total number of atoms or molecules in a given sample, we should multiply the number of moles with Avogadro’s constant. Given below is the formula for that,

Number of atoms or molecules=Number of moles*6.022*1023

The following form is considered as the relation between the atomic mass unit (amu) and the gram,

1 amu= 1 gram6.022*1023=1.66*10-24 grams

Hence the mass of one mole of an element will be equal to its atomic mass in grams. 

Number of electrons in a mole of hydrogen molecule

Hydrogen molecule contains the following number of electrons in a mole; 1 mole of H2 consists of 6.023*1023 molecules and each molecule of H2 has two electrons.

1 mole = 6.023*1023

Interesting Facts:

• 6.022 * 1023 pennies; would be able to make at least 7 stacks that would reach the moon.
• 6.022 * 1023 watermelon seeds; can be found inside a melon which could be slightly larger than the moon.
• 6.022 * 1023 blood cells; are more than the total number of blood cells found in every human on earth

Applications of mole

• Moles are very helpful in determining the chemical reaction on a macroscopic level. For example, whenever a mole of water undergoes decomposition, it is likely to release 1 mole of hydrogen gas and 0.5 moles of oxygen.
• The mole concept is used to define the molarity of a substance. Molarity is nothing but the number of moles of a solute contained in a 1-litre volume of a solution.
• Similar to the molarity concept, there is also the concept of molality. Molality also depends on the number of moles. The molality of any substance can be determined using the number of moles contained in 1 kilogram of a solvent.

Frequently Asked Questions

1. What is the importance of the mole concept?

The mole is nothing but the unit of the amount in chemistry. It can provide a bridge between the atoms and the macroscopic material that we work on in the labs. The mole concept allows the chemists to weigh in amounts of two substances, for example, iron and carbon, for equal numbers of iron and carbon atoms are easily obtained. 

A mole of a substance can be illustrated as the mass of the substance, which consists of the same number of essential units as there are atoms in exactly 12 g of 12 C.

2. How many moles does gold contain?

The molar mass of gold is 196.96657 g/m. The molar mass of gold can be defined as the mass of 1 mole of gold atoms which can be typically mentioned in grams. Henceforth, the gold’s molar mass can be specified in units of grams/mole (g/m). This can also be called the molecular weight of gold. 

3. What is the reason behind selecting carbon – 12 as the standard element for atomic mass?

The following are the main reasons why carbon – 12 is selected as a standard to measure atomic mass. Among the carbon isotopes, C – 12 seems to contain the most stable isotope compared to C – 13 and C – 14. Secondly, the natural abundance of C – 12 is valued at 98.89 %, which is relatively higher than the abundances of C – 13 and C – 14. More importantly, carbon compounds have higher stability and abundance.

4. Who is responsible for the discovery of the value of 1 mole?

An Italian scientist in the 19th century named Amedeo Avogadro is the person who invented the value of 1 mole. The value of one mole is 6.022*10²³. This is widely referred to as the Avogadro constant or number. Amedeo Avogadro discovered that under the same temperature and pressure, two gases that contain the same volume consist of the same amount of molecules.

5. Is mole fraction equal to partial pressure?

In any mixture, the partial pressure of each gas can be seen as proportional to the mole fraction. The pressure exerted by each gas (its partial pressure) in the given mixture of gas is independent of the pressure exerted by all other gases present in the gas mixture.

6. What is the main reason to use mole fraction?

The fraction can determine the number of single component moles (or molecules) divided by the total amount of moles (or molecules) in the mixture. Therefore, mole fraction is very useful when two reactive components are mixed, as the ratio of both the components is understood if the mole fraction of each is known.

7. What are the three significance of mole?

The following are the three significant capabilities of a mole. The mole concept provides a detailed explanation of the properties of water. The mole concept can give us a universally approved standard for measuring masses. The mole concept also plays a vital role in establishing a standard for the stoichiometry of reactions.

8. How does chemistry work with moles?

Atoms and molecules are very minute particles. The main application of a mole concept is to identify the values of macro substances such as atoms or molecules. In chemistry, mole concept basics are utilised to calculate small objects.

9. What is the main purpose of mole unit fraction?

A mole unit fraction is a number of single component molecules (or moles) divided by the total number of molecules (or moles) in a given mixture. In this case, if two reactive components are mixed, a mole fraction can be found very helpful since the ratio of both the components can be understood if a mole fraction is known for each component.