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Avogadro's Number - Importance, History, Significance, Practice Problems & FAQs

Avogadro's Number - Importance, History, Significance, Practice Problems & FAQs

Have you ever gone shopping for fruits at a local fruit vendor’s market?

You might have seen that the vendor would use different kinds of counting systems to measure the quantities of fruits like kilograms, dozens etc. One of the measuring units is the weight (kg) while the other measuring unit is the quantity (dozen).

Depending upon one’s convenience, we may use whichever counting system.


Going along the same flow, even the constituent particles in any substance are quantified using a specific unit. The question here is, what is that unit? Who established the value of the said unit?

The quantity of constituent particles of any substance is determined in terms of Avogadro’s number. However, the value of Avogadro’s number 6.022×1023 or NA was not estimated by Avogadro, but the contribution of Avogadro is enormous in the chemical world. Avogadro was the first person who coined the term molecule, he was one of the pioneers in the development of atomic theory and explained the atoms and their form of existence. For example, a hydrogen atom is H but it can exist in form of H2, an oxygen atom is O but it can exist or form O2 and O3.

Table of Contents

  • What is Avogadro’s Number?
  • Avogadro’s Constant: Its Importance
  • How was Avagadro’s Number Determined?
  • Significance of Avogadro’s Number
  • Practice Problems
  • Frequently Asked Questions (FAQs)

What is Avogadro’s Number?

Avogadro’s number tells us the number of particles in 1 mole of a substance. These particles could be electrons or molecules or atoms or ions. The value of Avogadro’s number is approximately 6.022140857 × 1023

Hence if you want to determine the number of particles in 3 moles of a substance, it can be calculated as:

= 3 ×6.022140857 × 1023 particles

= 1.8066 ×1024 particles

Avogadro's Constant: Its Importance

It creates a bridge between the macroscopic world and the microscopic world by relating the quantity of the substance to the number of particles. It also provides the relationship between properties and other physical constants. Some of them are:

Relationship between Boltzmann (kB) constant and gas constant (R): R=kBNA

Relationship between the fundamental charge (e ) and the Faraday’s constant (F): F=NA e

Relationship between molar mass (Mu) and atomic mass unit (u): 1 u=MuNA

In chemistry, we always take a macroscopic approach to measure the properties of the substances like measuring the total volume of a substance, or the temperature, or the mass of a substance. But if we look at the atomic level, knowledge of the momentum and velocity of particles is important. Both of these are connected by Avogadro's number.

How was Avagadro’s Number Determined?

Avagadro has grown during the important period of development of chemistry. Many chemists like Gay-Lussac, and John Dalton debated how these small atomic particles behaved. As they started to understand the fundamental properties of atomic particles. Avagadro was particularly intrigued by Gay-Lussac's law of combining volumes.

Avogadro played around with the effects of this law and predicted that for it to hold true, equivalent volumes of any two gases at comparable weights and temperatures must hold particles of equivalent numbers. And to prove that this law might be accurate as if there were a clear difference between molecules and atoms as if certain elements, like hydrogen, actually existed as molecules. Avogadro lacked terminology like "molecule" to explain the theory and his ideas encountered resistance from people like John Dalton. Later, Stanislao Cannizzaro gave Avogadro's theories attention but by the time he got this recognition, he was already passed away.

Chemist Jean Baptiste Perrin decided to announce the number in the name of Avogadro's law because it was so important to the development of chemistry.

Significance of Avogadro’s Number

A substance's mass is measured in terms of atomic mass units. The definition of an atomic mass unit is the mass of one carbon atom divided by twelve. For instance, hydrogen has a mass of 1.00794 amu. Chemists came up with a way to link the atomic mass unit and the gram using Avogadro's number.

1 g = 6.022 ×1023 amu

 1 amu = 1.66 ×10-24 grams

Using this, we are now able to convert between measurements in grams and atomic mass units (amu).

Recommended Video Link


Practice Problems

Q1. Which of the following is the correct value of Avogadro's number?

A. 6.022140857 × 1023B. 6.022140857 × 1022C. 6.022140857 × 1024D. 6.022140857 × 1021

Answer: (A)

Solution: Avogadro’s number tells us the number of particles in 1 mole of a substance. These particles could be electrons or molecules or atoms or ions. The value of Avogadro’s number is approximately 6.022140857 × 1023

Q2. 2 moles of H2O contains _____ number of molecules.

A. 6.022140857 × 1023B. 6.022140857 × 1022C. 12.044281714 ×1022D. 12.044281714 ×1023

Answer: (D)

Solution: 1 mole of any compound will contain 6.022140857 × 1023 number of molecules.

Hence, 2 mole of H2O will contains = 2×6.022140857 × 1023=12.044281714 ×1023  number of molecules.

Q3. How many particles will be there in 1.6 g of methane?

A. 6.022140857 × 1023B. 6.022140857 × 1022C. 6.022140857 × 1024D. 6.022140857 × 1021

Answer: (B)

Solution: 1 mole of any compound will contain 6.022140857 × 1023 number of molecules.

Number of moles =Given mass of methaneMolar Mass of methane=1.6 g16gmole=0.1 mol

0.1 mol of CH4 contains = 0.1 ×6.022140857 × 1023 =6.022140857 × 1022 molecules 

Q4. Which of the following symbols represents Avogadro's Number?

D. All of the above

Answer: (A)

Solution: Avogadro's number is represented by NA. The value of NA=6.022140857 × 1023

Frequently Asked Questions - FAQs

Q1. Does Avogadro’s number have any units?
Avogadro’s number is a dimensionless quantity. It represents the number of units which can be an atom, molecules, ions or electrons. Hence, it doesn’t have any units.

Q2. Are the mole and Avogadro's number equivalent?
No, A mole is a unit used to measure the quantity of any substance or the number of particles in any substance. The number of atoms in one mole of a particular substance is known as Avogadro's number.

For example, 1 mole of carbon contains 6.022140857 × 1023 number of carbon atoms.

Q3. Is it possible to calculate the mass of an atom using Avogadro’s number?
Yes, it is very convenient to calculate the mass of an atom using Avogadro’s number.

Let’s calculate the mass of 1 oxygen atom.

1 mole of oxygen contains = 6.022140857 × 1023number of oxygen atoms.

Mass of 1 mole of oxygen =16 g

16 g of oxygen contains = 6.022140857 × 1023 number of oxygen atoms

Hence, the mass of one oxygen atom = 16 g6.022140857 × 1023= 2.6568×10-23 g

Q4. Does the value of Avogadro's number change in presence of any external factor?
No, the value of Avogadro’s number won’t change in any circumstances. It is a constant quantity. For example, 1 dozen means 12 pieces, which is constant everywhere. Similarly, Avogadro’s number is also a constant quantity.


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