Mole and Avogadro's Number explained

len Alfred Ajibola - 25th August, 2022 @ 07:07 PM

Topics in Chemistry

Avogadro's number explained with worked examples Mole and Avogadro's Number explained Le Chatelier's Principle: Changes in concentration and pressure in dynamic equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures What are mixtures? Characteristics of mixtures Physical properties of matter Chemical properties of matter explained with examples Differences between physical and chemical change in chemistry Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid state of matter: Characteristics of liquids Gaseous state of matter: Characteristics of gases Molar Mass, worked examples and differences with molecular mass

Academic Questions in Chemistry

Please click here to see all Questions and Answers

Which of the following isn't an element of the periodic table.

  • A. J

  • B. Y

  • C. W

  • D. B

  • E. U

  • F. K

According to the periodic table, elements in the same group have got the same number of shells.

  • A. True

  • B. False

The periodic table of elements is also called the Mendeleev's table.

  • A. True

  • B. False

The simplest formula of a compound is termed _____.

  • A. Emperical formula

  • B. Molecular formula

  • C. Avogadro's number

  • D. Mass formula

  • E. Molar mass formula

  • F. Mole ratio

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)

  • A. FeO

  • B. Fe2O3

  • C. Fe3O4

  • D. FeO2

  • E. Fe3O6

  • F. Fe2O4

Which of the following statement is false concerning hydrocarbons?

  • A. Hydrocarbons can be aromatic

  • B. Hydrocarbons are made up of carbon and hydrogen only

  • C. Alkynes are aliphatic hydrocarbons

  • D. Alkenes have a carbon-carbon double bond in their structure

  • E. Benzene ring has a carbon-carbon triple bond in its structure

  • F. Hydrocarbons are the main constituents of petroleum and natural gas

The ability of carbon to form long chain of itself is called _____.

  • A. Carbon chain reaction

  • B. Catenation

  • C. Carbontion

  • D. Carbontion

  • E. Organic chemistry

  • F. Carbon moleculation

Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).

  • A. 13.00894 amu

  • B. 11.00206 amu

  • C. 12.00794 amu

  • D. 14.001 amu

  • E. 15.001 amu

  • F. 16.033 amu

Concept of Mole:

The mole is a unit of measurement. In fact, it is one of the important units of measurement in chemistry. It is a basic unit that measures the quantity or amount of a substance. Similarly, Avogadro's number is a fundamental constant in chemistry which enables students and teachers to compare the atoms or molecules of various substances with the mole as a quantitative unit. This was theorized by an Italian scientist named Amadeo Avogadro in 1811.

Please read on fundamental quantities here

The mole is a crucial concept in chemical equations and calculations since the quantity of reactants and products are reflected in it, and must be balanced in both directions. This is explained via the equation below:

2H2(g) + O2(g) -> 2H2O(l)

From the above equation, the values in front of each reactants and product represents the mole. We can therefore state that two moles of hydrogen molecule reacts with one mole of oxygen molecule to produce two moles of water molecules. Meanwhile, understand that when no value is present in front of a reacting element, molecule or substance, one mole is attributed to it. This also holds true for one or more products.

You can read on Graham's law of diffusion here

The key point to note in the above paragraph is the fact that the concept of mole is attributed to the measurement of substances. In short, mole is often referred to as the amount of substance 'n'.

Note: Just as mass is expressed in grams and length in meter, the mole is expressed in 'mol' and it is a unit of measurement.

Please read on molecular mass here

Mole and Avogadro's Number

It is worthy of note to always understand that the mole of any substance is related to a constant called Avogadro's number. This Avogadro's number or constant is the number of particles (or atoms) contained in one mole of any substance. To make it clearer, think of it this way: 'one may choose to buy a cup of rice'. This 'cup' is the unit of measurement in this instance. However, the number of rice particles present in this cup will represent the Avogadro's number in that regard. So let's assume that one cup of rice will always contain ten thousand (10,000) rice particles. In this regard, for every cup of rice measured, we will have 10,000 rice particles inside it.

Mole and Avogadro's number

Please read on molar mass here

Now, recall that atoms are the smallest particles of an element that can take part in a chemical reaction. With regards to quantitative measurements in chemistry, one mole of any substance will always contain 6.02214076 x 1023 particles within it. This number of particles contained in one mole of any substance is termed the Avogadro's number. Therefore, the mole may be referred to as the container (or cup in our above instance) while the number of atoms, particles or molecules it contains (rice in the above paragraph) is known as the Avogadro's number. This is the simplest summary of the relationship between the mole and Avogadro's number using a cup of rice as our instance.

You can read on elements and their characteristics here

Avogadro's number is defined as the number 6.02214076 × 1023 and it specifies the number of atoms, molecules or particles present in one mole of any substance. This number is also referred to as Avogadro's constant.

Understand that the number 6.02214076 × 1023 is also the number of atoms that was calculated to exist in exactly 12 grams of carbon-12. Interestingly, it turned out to be experimentally determined as the number of particles in one mole of any substance.

Just as 12 is a constant number (or value) for a dozen and 144 represents a constant value for gross, the Avogadro's number '6.02214076 x 1023' will always remain a constant value for one mole of any substance, be it an element, a molecule or a compound. This is summarized in the image below:

Mole and Avogadro's number

Please read on Dalton's atomic theory and its modifications here

Importantly, it is noteworthy to state that regardless the elements, molecules or substance involved in measurement, one mole will always contain 6.02214076 x 1023 particles or atoms. For this reason, one mole of magnesium (Mg), one mole of water (H2O) and one mole of sodium chloride (NaCl) will still contain the same number of particles and that is 6.02214076 x 1023.

Recall that magnesium is an atom while water and sodium chloride are molecules respectively. However, sodium chloride can also be considered as a compound. Be that as it may, all are still weighted or quantified as one mole since no value is present in front of their respective chemical formula or symbol. With reference to our previous instance, this number of particles is a function of the 'measuring container or cup' (mole) which always has a constant amount of atoms or particles it can hold regardless whatever element, molecule or substance is within it.

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Amazing facts in Chemistry

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals.

Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools

Water freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre


In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.

Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:

  1. Alkanes

  2. Alkenes

  3. Alkynes

They are shown in the image below:

Alkanes, Alkenes and Alkynes - Len Academy

It's important to note the followings:

  • Alkanes have single bonds (only) in their structures.

  • Alkenes always have a carbon-carbon double bond present in their structure.

  • Alkynes always have a carbon-carbon triple bond present in their structure.


Aromatic hydrocarbons are classified into:

  • Arenes: They contain benzene ring as a structural unit. Below is the structure of a benzene ring.

Benzene Ring - Len Academy


  • Nonbenzenoid aromatic hydrocarbons: They possess special stability but lack a benzene ring as a structural unit.

Organic chemistry is the study of carbon and it's compounds.

Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.

Please read the introduction to organic chemistry here

A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.

Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.

The large molecules (above) have no specific chemical formula throughout their volume.

Please read more on carbohydrates and sugars here

Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the modifications of Dalton's atomic theory.

Please read on Dalton's atomic theory and its modifications here.

Calculate the Relative Molecular Mass of methane (CH4). (Carbon=12.001 and H=1.00794)

  • Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen

  • Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.

  • 12.001 + (1.00794 x 4)

Molecular Mass of Methane = 16.033 amu

Please read more on molecular mass here

Calculate the Relative Molecular Mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)

  • Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen

  • Water contains 2 atoms of Hydrogen and 1 atom of oxygen.

  • (1.00794 x 2) + 15.9994

Molecular Mass of Water = 18.015 Da

Please read on emperical formula and its calculations here

Gold - Len Academy

Below are some facts about gold:

  • It is the only metal that has a gold (golden) color

  • Gold is present inside the earth crust in all the seven continents

  • Pure gold is soft and very stretchable (It can even be stretched into threads)

  • The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'

  • Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables

  • Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants

  • The term Gold originated from an ancient English word 'geolu' which means yellow

  • 24karat gold is the purest gold element

Please read more interesting facts about gold here