Mole and Avogadro's Number explained

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

Topics in Chemistry

Gas laws in chemistry Charles's law explained Calculation questions on Charles's law Examples of Charles's law in real life Boyle's law explained Calculation questions on Boyle's law Examples of Boyle's law in real life Summary on the kinetic molecular theory of gases Postulates of kinetic theory of gases 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

Academic Questions in Chemistry

Please click here to see all Questions and Answers

With regards to redox reactions, which of the following statement is wrong?

  • A. Redox reaction are examples of chemical change

  • B. Reduction is the gain of electron

  • C. Substances that donates election during chemical reaction are termed reductants

  • D. Oxidizing agents are always reduced in chemical reactions

  • E. Oxidation occurs at the cathode in electrolysis

  • F. Hydrogen is a reducing agent

In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.

  • A. True

  • B. False

_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.

  • A. Outer

  • B. Excess

  • C. Valence

  • D. Positive

  • E. Negative

  • F. Last

_____ is the negative electrode in electrolysis.

  • A. Anode

  • B. Anion

  • C. Cathode

  • D. Cation

  • E. Ion

  • F. Electrolyte

Electrovalent Bond - Len Academy

The above diagram shows the _____ type of bond.

  • A. Covalent

  • B. Polar covalent

  • C. Coordinate covalent

  • D. Metallic

  • E. Van dear walls

  • F. Ionic

 Metals are referred to as _____ in their impure state.

  • A. Diluted

  • B. Consecrated

  • C. Coloured

  • D. Ores

  • E. Stained

  • F. Strained

Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.

  • A. State

  • B. Ductility

  • C. Luster

  • D. Malleability

  • E. Hardness

  • F. Inflorescence

The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.

  • A. Mole

  • B. Volume

  • C. Weight

  • D. Number of moles

  • E. Mass

  • F. Amount of substance

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

Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years

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

Notable points in Chemistry

Periodic Table - Len Academy

The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.

Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.

The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.

Please read on the periodic table of elements here.

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)

  • Solution:

Step 1: Identify the given parameter from the question.

  • Fe = 69.94%,   O = 30.06%.

  • Empirical formula = Fe?O?


Step 2: Convert the percentages to gram. (just attribute grams to the %).

  • 69.94% = 69.94g while 30.06% = 30.06g


Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.

  • Mole of Fe: 69.94/55.85 = 1.252mol

  • Mole of O: 30.06/16 = 1.879mol


Step 4: Divide both sides by the smallest mole ratio.

  • Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1,    1.879/1.252 = 1.5

  • We now have the formula = Fe1O1.5


Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.

  • For iron (Fe), we will have 1 x 2 = 2

  • For oxygen (O), we will have 1.5 x 2 = 3


Step 6: Write the empirical formula.

  • The empirical formula= Fe2O3

  • Iron(III)tetraoxosulphate(VI)

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.