We commonly use a unit dozen or unit gross for counting of materials or goods. For example, one dozen pens means 12 pens or one dozen bananas means 12 bananas. Similarly, one gross books means 144 books or one gross apples means 144 apples.

In a similar way, chemists use the unit mole for counting of atoms, molecules, ions, etc. in the chemistry. So, let’s understand the definition of mole in chemistry in very simple words.

## Definition of Mole in Chemistry

In 1896, Ostwald introduced the term mole. It is a Latin word “**moles**” meaning heap or pile. A mole (mol) is a unit of measurement in chemistry that represents a specific number of particles, such as atoms, molecules, or ions. A simple definition of mole is as:

The number of atoms in exactly 12.00 grams of carbon atoms is called a mole. In other words, the amount of a substance that contains the same number of particles as in 12g of carbon-12 is called a mole.

The number of atoms present in 12 g of carbon-12 has been calculated experimentally to be 6.02 x 10^{23}. This number is known as Avogadro’s number, named in honor of Amedeo Avogadro.

## What is Avogadro’s Number

Avogadro’s number is a fundamental constant that represents the number of particles in one mole of a substance. It is denoted by N_{A}. The value of Avogadro’s number is 6.02 x 10^{23}, meaning that one mole of any substance contains 6.02 x 10^{23} particles. These particles may be atoms, molecules, ions, electrons or anything else.

Thus, 1 mole of hydrogen atoms means 6.02 x 10^{23} hydrogen atoms. Similarly, 1 mole of hydrogen molecules means 6.02 x 10^{23} hydrogen molecules. One mole of water molecules is equal to 6.022 x 10^{23} water molecules.

In the similar way, one mole of potassium ions contains 6.02 x 10^{23} potassium ions. One mole of electrons contains 6.02 x 10^{23} electrons.

You must specify the type of entity when you use the mole designation. For example, a mole of oxygen atoms contains 6.02 x 1023 oxygen atoms. Similarly, a mole of oxygen molecules contains 6.02 x 1023 oxygen molecules. Therefore, a mole of oxygen molecules contains two moles of oxygen atoms, i.e. 2 x 6.02 x 1023 oxygen atoms.

## How much does one mole weigh?

The weight of one mole depends on the nature of particles (or units). The mass of one mole atoms of any element is exactly equal to the atomic mass in grams (gram-atomic mass) of that element. For example, the atomic mass of aluminum is 27u. You know 1u is equal to 1.66 x 10^{-24} grams.

One mole of aluminum contains 6.02 x 10^{23} aluminum atoms.

So, the mass of one atom aluminum = 27 x 1.66 x 10^{-24} g

Mass of one mole aluminium = 27 x 1.66 x 10^{-24} X 6.02 x 10^{23} = 27g

It is the atomic mass of aluminum in grams, or it is one gram atomic mass or one gram atom of aluminum.

In the same way, the mass of 6.02 x 10^{23} molecules (i.e. 1 mole) of a substance is equal to its molecular mass in grams or gram-molecular mass or gram molecule. For example, the molecular mass of water (H_{2}O) is 18u.

Thus, the mass of one mole of water will be 18 x 1.66 x 10^{-24} x 6.02 x 10^{23} = 18 g. It is the molecular mass of water in grams or one gram-molecular mass or one gram molecule.

## Why are Moles Important in Chemistry?

Moles are an important fundamental concept in chemistry that allows chemists to determine the amount of a substance present in a given sample. This information is vital for determining reaction stoichiometry, which involves balancing chemical equations and predicting the amount of product that will form in a chemical reaction.

## What is Molar Mass

**Molar mass** is the mass of one mole of a substance in grams. We express it in grams per mole (g/mol). We can calculate the molar mass of a substance by adding up the atomic masses of all the atoms in a molecule.

Thus, we can calculate the molar mass of water (H_{2}O) by adding the atomic masses of two hydrogen atoms (1.008 g/mol each) and one oxygen atom (16.00 g/mol). Thus,

Molar mass of water = 2 x 1.008 + 1 x 16.00 = 18.02 g/mol.

Thus, we can say that the molar mass in grams is numerically equal to atomic/molecular/ formula mass in u.

Molar mass of water = 18.02 g mol^{-1}

Similarly, molar mass of sodium chloride = 58.5 g mol^{-1}

## How to Calculate Number of Moles?

We can calculate the number of moles of a substance using its mass and molar mass. The formula for calculating the number of moles is:

**Number of moles of a substance** = Mass of substance in grams / Molar mass

For example, if we have 10 grams of water (H2O), we can calculate the number of moles as:

Molar mass of water = 2 * 1.008 + 1 * 16 = 18.02 g/mol

Number of moles of water = Mass of water in grams / Molar mass = 10 g / 18.02 g/mol = 0.555 mol

Thus, to calculate the number of moles of a substance in a sample, we need to know the mass of the sample and the molar mass of the substance.

## How to Calculate Mass from Moles?

Conversely, we can also calculate the mass of a substance if we know the number of moles and the molar mass of the substance.

Let’s take an example of carbon dioxide (CO_{2}), which has a molar mass of 44.01 g/mol. Suppose we have 2 moles of CO_{2}. To calculate the mass of CO_{2} in the sample, we can use the following formula:

Mass of substance in the sample = Moles x Molar Mass

Mass of CO_{2} = 2 mol x 44.01 g/mol = 88.02 g

Therefore, we have 88.02 grams of carbon dioxide (CO_{2)} in the given sample.

## How to Calculate Moles from Volume?

Besides mass, we can also calculate the number of moles of a gas from its volume at a given temperature and pressure. We can use the ideal gas law, which relates the pressure, volume, temperature, and number of moles of a gas.

Let’s take an example of hydrogen gas (H_{2}) at a pressure of 1 atm and a temperature of 25°C (298 K). Suppose we have 2 liters of hydrogen gas. To calculate the number of moles of H_{2} in the sample, we can use the ideal gas law as:

Ideal gas equation, PV = nRT

Here, P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature in Kelvin.

n = PV / RT

n = (1 atm x 2 L) / (0.08206 L atm/mol K x 298 K) = 0.0825 mol

Therefore, we have 0.0825 moles of H_{2} in the given sample.

### Google FAQs

### 1. What is the difference between a mole and a molecule?

A mole is a unit used to measure the amount of a substance, while a molecule is a group of atoms bonded together.

### 2. How is Avogadro’s number related to the concept of a mole?

Avogadro’s number is the number of particles (atoms, molecules, or ions) in one mole of a substance.

### 3. Can moles be used to measure the amount of a liquid or gas?

Yes, moles can measure the amount of a liquid or gas, but we must also consider the volume and temperature of the sample.

In chemistry, moles are a fundamental concept that is used to measure the amount of a substance in a given sample. They are primal for calculating reaction stoichiometry, determining concentration, and predicting the amount of product formed in a reaction.

In this tutorial, you have known about moles in chemistry with examples. Hope that you will have understood the basic points and practiced all examples.