Chemistry Formulas

Number of Moles Formula

A mole is a unit defined for the amount of substance. It is in the International System of Units (SI) and its short form is “mol”. It is the mass of that substance contains the same number of fundamental units such as atoms in 12.0 grams of 12 C. These fundamental units may be atoms, molecules, or formula units based on the substance. It is representing the number of chemical elements.  This article will define the mole and number of moles formula with examples. Let us begin it!

Number of Moles Formula

Source: wikihow.com

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Number of Moles Formula

What is a mole?

The mole concept is a simple and convenient method for expressing the amount of a substance in chemical applications. We may have the measurements into two steps, one is the numerical magnitude and the other is the units in which the magnitude is expressed in.

For example, when we say that the mass of a ball is 2 kilograms, then 2” is the magnitude and the unit is ‘kilogram’. However, dealing with the particles at an atomic or molecular level, this traditional concept will not work. Because even one gram of a pure element will contain a huge number of atoms. That’s why we are using the mole concept.

Mole concept is mainly focused on the unit ‘mole’. It is a count of a very large number of particles. One mole of any substance is equal to the Avogadro number. This number as value \(6.023 \times 10^{23}\). It is useful to measure the products in any chemical reaction.  Thus \(6.023 \times 10^{23}\) of atoms, molecules or particles are 1 mol of atoms, molecules or particles.

The formula for Number of Moles

The number of moles formula is given as follows:

Number of Moles = \(\frac {Mass\; of \; substance} {Mass \;of \; one \; mole}\)

Uses of Mole Concept

The mole unit is very important and useful in chemistry. It is the base of the stoichiometry and it is providing the best option for expressing amounts of reactants and products consumed and formed during any chemical reaction. We may write all the chemical reactions as a mole relation.

For example in the following reaction:

\(2 H_{2} + O_{2} \rightarrow  2H_{2}O\),

It means 2 mol of diatomic hydrogen will react with 1 mol of diatomic oxygen to produce 2 mol of water.

It is also useful for representing concentration units like the molarity with the unit of mol \(L^{-1}\) i.e. mole per litre or molecular weight.

Solved Examples

Q.1: Find out the number of moles in 0.325 grams of barium hydroxide.

Solution:

Given values are:

Mass of \(Ba(OH)_{2}\) = 0.325 gram

Molar mass i.e. the mass of one mole of \(Ba(OH)_{2}\)  is 171 gram.

Number of moles formula is:

Number of Moles = \(\frac {Mass\; of \; substance} {Mass \;of \; one \; mole}\)

Substituting the values,

Number of Moles = \(\frac {0.325} {171}\)

Number of Moles    = 0.00190 mol.

Q.2: Find out the number of moles in 190 grams of \(MnO_{2}\).

Solution:

Given values in the problem are,

Mass of \(MnO_{2}\) = 190 gram

Mass of one mole of  \(MnO_{2}\) = 86.94 g

Now, formula is given as:

Number of Moles = \(\frac {Mass\; of \; substance} {Mass \;of \; one \; mole}\)

Putting the values,

Number of Moles = \(\frac {190} {86.94}\)

Number of Moles = 2.184 mol.

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