Reduction and Oxidation


The concept of Reduction and Oxidation is very important for the students preparing for competitive exams like JEE, NEET, RRB NTPC, SSC CGL, SSC CHSL, CDS, NDA, etc . Here we have discussed about the important terms like reduction, oxidation, redox reaction, and the ways to calculate oxidation number.

1. Classical concept of oxidation and reduction

What is Oxidation?

Oxidation is a reaction in which there is addition of oxygen or removal of hydrogen. It is also defined as a reaction in which an electronegative element or group is added or an electropositive element or group is removed.

Examples of Oxidation

Oxidation of Mg

2Mg + O2 → 2MgO

Oxidation of H2S

H2S + Cl2 → 2HCl + S

Oxidation of Fe

Fe + S  → FeS

Oxidation of KI

2KI + H2O2 → 2KOH + I2

What is Reduction?

Reduction is a reaction in which there is addition of hydrogen or removal of oxygen. It is also defined as a reaction in which an electropositive element or group is added or an electronegative element or group is removed.

Examples of Reduction

Reduction of Cl2

H2 + Cl2→ 2HCl

Reduction of CuO

CuO + C → Cu + CO

Reduction of HgCl2

HgCl2 + Hg →  Hg2Cl2

Reduction of FeCl3

2FeCl3 + H2 → 2FeCl2 + 2HCl

1.1. Oxidation Vs Reduction

 

Oxidation

Reduction

Addition of

Oxygen

Hydrogen

Electronegative element/group

Electropositive element/group

Removal of

Hydrogen

Oxygen

Electropositive element/group

Electronegative element/group

 

2. Modern concept of oxidation and reduction

According to modern concept, oxidation is defined as loss of electrons and reduction is defined as gain of electrons.

Oxidation and Reduction (Modern Concept)

Na  →  Na+ + e (Oxidation of Na)

Cl2 + 2e → 2Cl- (Reduction of Cl­2)

Zn → Zn2+ + 2e (Oxidation of Zn)

S + 2e → S2- (Reduction of S)

 

3. Effects of Oxidation in Everyday Life

Corrosion and rancidity are effects of oxidation reaction in everyday life. Rusting of iron, black coating on silver and the green coating on copper are examples of corrosion. Fats and oils become rancid and their smell and taste change when they are oxidized. Antioxidants are substances that prevent oxidation. They are added to foods having fats and oils. Foods are kept in air tight containers to slow down oxidation.

4. What is an Oxidizing agent?

Oxidizing agent (oxidant) is a substance that undergoes reduction and that is acceptor of electrons. It is the substance which gets reduced. Its oxidation number is reduced. Oxygen (O­­2), ozone (O3), hydrogen peroxide (H2O2), potassium permanganate (KMnO4), potassium dichromate (K2Cr2O7) are some examples of oxidizing agents.  

1. CuO + C   Cu + CO (In this reaction, CuO undergoes reduction. Hence, it is an oxidizing agent.)

2. Zn(s) + 2HCl (aq) ZnCl2 (aq) + H2 (In this reaction, there is a reduction in oxidation number of H from +1 to 0. H is reduced in this reaction. So, H in HCl is the oxidizing agent.)

5. What is a Reducing agent?

Reducing agent (reductant) is a substance that undergoes oxidation and that is donor of electrons. It is substance which gets oxidized. Its oxidation number is increased. Hydrogen (H2), sulphur dioxide (SO2), carbon monoxide (CO), hydrogen sulphide (H2S) and carbon (C) are examples of reducing agents.

1. H2O + C CO + H2 (In this reaction, C undergoes oxidation. Hence, it is a reducing agent.)

2. Zn(s) + 2HCl (aq) ZnCl2 (aq) + H2 (In this reaction, there is an increase in oxidation number of Zn from 0 to +2. Zinc is oxidized in this reaction. So, Zn is a reducing agent.)

Note:

Nitrous acid (HNO2), sulphur dioxide (SO2) and sulphurous acid (H2SO3) are both reducing and oxidising agents.

This is because N and S atoms occur in intermediate oxidation state in these substances.

6. Redox reaction

It is a reaction in which oxidation and reduction occur at the same time.

Redox Reaction

Other examples of Redox reactions are given below:

ZnO + C → Zn + CO

MnO2 + 4HCl → MnCl2 + 2H2O + Cl2

7. Oxidation Number

It is the charge found on atom of a molecule or ion. It is also known as oxidation state. An element’s oxidation number can never be higher than number of valence electrons found in it.

8. How to calculate oxidation number?

Oxidation number is calculated with the help of the rules given below.

  • An atom’s oxidation number in its free/elemental/uncombined state is zero. For example, oxidation number of H, S and P in H2, S8 and P4 is zero. The oxidation number of O is zero in both O2 and O3.
  • Oxidation number of ions made up of only one atom is same to the charge on ion. For example, oxidation numbers of Na+, Mg2+, Fe3+, Cl- and O2- ions are +1, +2, +3, -1 and-2 respectively.
  • Oxidation number of all alkali metals (Li, Na, K, Rb, Cs) in their compounds is +1.
  • Oxidation number of all alkaline earth metals (Be, Mg, Ca, Sr, Ba) is +2.
  • Oxidation number of Aluminium in all its compounds is regarded as +3.
  • In most compounds, oxygen has oxidation number of -2.
  • In peroxides (H2O2, Na2O2 etc), each oxygen atom has an oxidation number of -1.
  • In superoxides (KO2, RbO2), each oxygen atom has an oxidation number of -1/2.
  • Oxygen has an oxidation number of +2 and +1 in oxygen difluoride (OF2) and dioxygen difluoride (O2F2) respectively.
  • Hydrogen has oxidation number of +1. It has oxidation number of -1 when it bonds with metals in compounds having two elements (LiH, NaH and CaH2).
  • The oxidation number of fluorine is -1 in all its compounds. Oxidation number of remaining halogens (Cl, Br and I) is -1 when they are found as halide ions.
  • Sum of oxidation number of all atoms in a compound is zero.
  • Sum of all oxidation numbers of atoms of the ion is equal to the charge on the ion. For example, in carbonate ion, (CO3)2-, the sum of 3 oxygen atoms and 1 carbon atom must equal -2.  

Note:

In carbon dioxide (CO2), carbon occurs in its maximum oxidation state (+4). Further oxidation of carbon is not possible.

Carbon forms compounds in all oxidation states ranging from -4 (in CH4) to +4 (in CO2).

Oxidation state of Nitrogen in various compounds ranges from -3 to +5.

Examples showing how to calculate oxidation number:

1. Oxidation number of Mn in KMnO4  

Let us assume that oxidation number of Mn = X. According to previously given rules, Oxidation number of K = +1 and Oxidation number of O = -2.

1+X+ (-2) x 4 = 0

1+X-8 = 0

X = +7

Hence, oxidation number of Mn in KMnO4 is +7.

2. Oxidation number Cr in K2Cr2O7

Let us assume that oxidation number of Cr = X. According to previously given rules, Oxidation number of K = +1 and Oxidation number of O = -2.

1 x 2 + X x 2 + (-2) x 7 = 0

2 + 2X -14 = 0

2X – 12 = 0

X = +6

Hence, oxidation number Cr in K2Cr2O7 is +6.

Summary

Classical concept of oxidation: Oxidation is addition of oxygen or removal of hydrogen, addition of electronegative element/group or removal of electropositive element/group.

Classical concept of reduction: Reduction is addition of hydrogen or removal of oxygen, addition of electropositive element/group or removal of electronegative element/group

Modern concept of oxidation: Oxidation is loss of electrons.

Modern concept of reduction: Reduction is gain of electrons.

Effects of Oxidation in Everyday Life: Corrosion (Rusting of iron, black coating on silver and the green coating on copper), rancidity of fats and oils.

Oxidizing agent (oxidant): undergoes reduction, acceptor of electron, gets reduced, its oxidation number is decreased, examples (O­­2, O3, H2O2, KMnO4, K2Cr2O7)

Reducing agent (reductant): undergoes oxidation, donor of electrons, gets oxidized, its oxidation number is increased, examples (H2, SO2, CO, H2S, C)

Redox reaction: A reaction in which oxidation and reduction occur simultaneously.

Oxidation Number: Charge found on atom of a molecule or ion. It can never be higher than number of valence electrons found in an element.

Frequently Asked Questions (FAQs) about Oxidation and Reduction Reactions

What is the difference between oxidation and reduction according to modern concept of oxidation and reduction?

According to modern concept of oxidation and reduction, the difference between oxidation and reduction is that oxidation is loss of electrons and reduction is gain of electrons.

What is oxidation?

Oxidation is a reaction in which there is loss of electrons or gain of oxygen or loss of hydrogen.

What is reduction?

Reduction is a reaction in which there is gain of electrons or loss of oxygen or gain of hydrogen.

Define oxidizing agent and provide examples of oxidizing agents.

Oxidizing agent (oxidant) undergoes reduction. It is acceptor of electron. It gets reduced. Its oxidation number is decreased. O2, O3, H2O2, KMnO2, K2Cr2O7 are some oxidizing agents.

Define reducing agent and provide examples of reducing agents.

Reducing agent (reductant) undergoes oxidation. It is donor of electrons. It gets oxidized. Its oxidation number is increased. H2, SO2, CO, H2S, C are some reducing agents.

What is oxidation number of an atom in its free/elemental/uncombined state?

An atom’s oxidation number in its free/elemental/uncombined state is zero.

What is the oxidation number of all alkali metals in their compounds?

Oxidation number of all alkali metals (Li, Na, K, Rb, and Cs) in their compounds is +1.

What is the value of oxidation number of all alkaline earth metals?

Oxidation number of all alkaline earth metals (Be, Mg, Ca, Sr and Ba) is +2.

What is the sum of oxidation number of all atoms in a compound?

Sum of oxidation number of all atoms in a compound is zero.

Name the compounds in which oxygen has (+) oxidation number.

In most compounds, oxygen has oxidation number of -2. Oxygen has an oxidation number of +2 and +1 in oxygen difluoride (OF2) and dioxygen difluoride (O2F2) respectively.

REPUBLIC DAY OFFER get 25% Off
Use Coupon code REPUBLIC

six months current affairs 2022 july december Rs.199/- Read More
half yearly current affairs july december july december 2022 in detail Rs.219/- Read More
half yearly current affairs in hindi jul dec 2022 in detail Rs.219/- Read More
six months current affairs 2022 book in hindi july december Rs.199/- Read More

0
COMMENTS

Comments

Share Blog



Current Affairs

Attempt Daily Current
Affairs Quiz

Attempt Quiz