Mole Concept: Definition, Calculation, and Examples

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What is Mole Concept

The mole concept is an appropriate method of expressing the amount of a substance.

Any measurement can be fragmented down into two parts – the numerical magnitude and the units that the magnitude given is stated in. For instance, the mass of a ball was measured to be 5 kilograms, the magnitude of this is ‘5’, and the unit is expressed in ‘kilogram’.

What is Mole?

The word “mole” was announced by the German chemist Wilhelm Ostwald in 1896, who derived this term from the Latin word moles that means a ‘heap’ or ‘pile.

In the arena of chemistry, a mole is defined as the amount of a substance that contains precisely 6.02214076 * 1023 ‘elementary entities’ of the given element.

The number 6.02214076*1023 is generally known as the Avogadro constant and is frequently represented by the symbol ‘NA’.

The elementary entities can be characterized in atoms, molecules, monoatomic/polyatomic ions, and other particles like electrons.

For example, one mole of a pure carbon-12 (12C) model will have a mass of precisely 12 grams and comprises of 6.02214076*1023 (NA) quantity of 12C atoms.

The number of moles of a substance in a given example can be denoted by the formula given below:

n = N/NA

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

N is defined as the total number of elementary entities present in the sample,

NA is defined as the Avogadro constant.

The uniqueness of a substance is defined not only by the types of atoms or ions it comprises but by the quantity of each type of atom or ion.

For instance, water, H2O, and hydrogen peroxide, H2O2, are identical in their respective molecules as they both are composed of hydrogen and oxygen atoms. But a hydrogen peroxide molecule encompasses two oxygen atoms, contrasting to the water molecule, which contains only one oxygen atom, the two substances show distinct properties.

The mole offers a link between an easily measured macroscopic property such as bulk or mass, and enormously essential property, the number of atoms, molecules, and so on.

Atomic Mass and Molecular Mass

The atomic mass of an element is defined as the mass of one atom of the element that is expressed in atomic mass units (amu).

It accounts for plenty of the numerous isotopes of the element and allocates an average value to the mass of one atom of the given element.

The atomic mass of a carbon-12 atom is 12 atomic mass units or amu, whereas the atomic mass of a carbon-13 atom is 13 atomic mass units or amu.

The atomic mass of an element is crudely equal to the sum of all the protons and neutrons present in the nucleus of a given atom.

The molecular mass of an element is defined as the sum of the atomic masses of all the components present in an element.

This quantity is also denoted in terms of atomic mass units. Hence, the molecular mass of water is always equal to the sum of all the atomic masses of its constituents present which are hydrogen and oxygen.

The atomic mass of hydrogen is equal to 1.00794 amu and the atomic mass of oxygen is equal to 15.9994 or 16 amu.

Since water molecules comprise of 2 hydrogen atoms and only one oxygen atom thus, the molecular mass of H2O will be 18.0154 amu.

Molar Mass

The molar mass of a given substance is the total mass of one mole of that substance.

It is denoted in terms of ‘grams per mole (g/mol). Though, the SI unit of the above-mentioned quantity is kg/mol. Molar mass can be represented by the formula written below:

The molar mass of a Substance = (Mass of the Substance in grams)/(Number of Moles)

Gram Atomic Mass vs Gram Molecular Mass

The gram atomic mass of an element is defined as the mass of one mole of a specific element. Correspondingly, the gram molecular mass of a compound is defined as the mass of a single mole of a particular compound. Hence, the gram atomic mass of hydrogen is roughly around 1.007g and the gram molecular mass of water or H2O is nearly around 18.015g.

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