MOLE CONCEPT

Introduction

Mole Concept And its Working Principle

The idea of mole is  a convenient way of expressing a substance’s quantity. We have two parts in measurement: the numerical magnitude and the units in which the numerical magnitude is expressed. The magnitude is ‘2’ and the unit is ‘kilogramme’ when the mass of a ball is measured to be 2 kilograms. 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.We are   primarily concerned with the mole which is a count of a vast number of particles.

Definition of a Mole

A mole is defined as the amount of a substance that includes exactly 6.02214076×1023 ‘elementary entities’ of the given substance in the discipline of chemistry.

The Avogadro constant is the quantity 6.02214076×1023 that is frequently symbolised by the symbol ‘NA’. Atoms, molecules, monatomic/polyatomic ions, and other particles are examples of elementary entities that can be represented in moles (such as electrons).

One mole of pure carbon-12 (12C) has a mass of exactly 12 grams and contains 6.02214076×1023 (NA) of 12C atoms.

The Avogadro constant is NA, and n is the number of moles of the substance (or elementary entity). N is the total number of elementary entities in the sample.

The Mole Idea 

A molecule’s number of moles may not necessarily match the number of moles of its constituent parts. A mole of water, for example, has a NA number of H2O molecules. Each water molecule, on the other hand, comprises two hydrogen atoms and one oxygen atom. One mole of H2O therefore includes two moles of hydrogen and one mole of oxygen.

Atomic and Molecular Masses

An element’s atomic mass is the mass of one of its atoms given in atomic mass units (amu). It takes into account the quantity of the element’s various isotopes and assigns an average mass to one atom of the element.

Because carbon samples typically include 98.89 percent carbon-12, 1.11 percent carbon-13, and minuscule amounts of carbon-14, the atomic mass of carbon is 12.011 atomic mass units. The atomic masses of these isotopes, however, differ.

A carbon-12 atom has a mass of 12 atomic mass units, while a carbon-13 atom has a mass of 13 amu. The total of all the protons and neutrons in an element’s nucleus is roughly equal to its atomic mass.

The molecular mass of an element is equal to the sum of its constituent elements’ atomic masses. The atomic mass units are also used to denote this amount. As a result, water’s molecular mass equals the total of the atomic masses of its constituents, hydrogen and oxygen.

Hydrogen has an atomic mass of 1.00794 amu, while oxygen has an atomic mass of 15.9994. The molecular mass of H2O  is 18.0154 amu because water molecules contain two hydrogen atoms and only one oxygen atom.

Molecular Weight

The total mass of one mole of a substance is defined as the molar mass of that substance. It is frequently expressed in ‘grammes per mole’ (g/mol). The SI unit for this number, however, is kg/mol. The following formula can be used to represent molar mass:

The molar mass of a substance is equal to (the mass of the substance in grammes) divided by (the mass of the substance in grammes) (Number of Moles)

Water, for example, has a molar mass of 18.015 g/mol, which is equal to the mass of NA number of water molecules.

Gram Molecular Mass and Gram Atomic Mass

The mass of one mole of an element is equal to its gram mass. In the same way, a molecule’s gramme molecular mass refers to the mass of a single mole of the chemical. As a result, the gramme atomic mass of hydrogen is around 1.007g, while the gramme molecular mass of water is about 18.015g.

The number of moles in a particular sample of an element/compound can be estimated by dividing the total mass of the sample by the element/molar compound’s mass, as shown in the formula below.

(Mass of the Sample)/(Number of Moles) (Molar Mass)

By multiplying the number of moles by the Avogadro constant, the total number of atoms/molecules in a sample can be estimated. This formula is worded as follows:

(Number of Moles) x (6.022 x 10²³) = Number of Atoms or Molecules

The following is the relationship between the atomic mass unit (amu) and the gramme:

1.66 x 10⁻²⁴ grams = 1 amu = (1 gram)/(6.022 x 10²³)

As a result, one mole of an element has the same mass as its atomic mass in grams.

The number of electrons in a molecule of hydrogen

In a mole of hydrogen, the number of electrons equals

Each molecule of H2 contains two electrons, and one mole of H2 comprises 6.023 x 10²³ molecules.

6.023 x 10²³ = 1 mole

As a result, the total number of electrons in a mole of H2 is 12.0461023.

Conclusion  

So we conclude that moles can be used to represent a chemical reaction on a macroscopic level. For example, if a mole of water undergoes decomposition, it releases 0.5 moles of oxygen and a mole of hydrogen gas.The concept of a mole is used in determining the molarity of a substance. Molarity is defined as the number of moles of a solute present in the one-liter volume of a solution.Similar to molarity, the concept of molality is also dependent on the number of moles. The molality of a substance is defined as the number of moles present in one kilogram of a solvent .