OXIDATION-REDUCTION [REDOX] REACTION

 

Week: ONE                        Date:     6-10/05/2019                                                     Time:

Period:                                 Duration: 1 HR 20 MIN.                                                 Average age of learners: 16YEARS

Subject:                               CHEMISTRY                                                                        Class: SS TWO

Topic:                                    OXIDATION-REDUCTION [REDOX] REACTION

Sub topic:

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials:

Entry behavior: The students have been taught chemical reaction

Behavioural objective: At the end of the lesson the students should be able to:

i.                     Define reaction.

ii.                   Explain the types of reaction.

iii.                  Define oxidation and reduction

iv.                 Find oxidation number of elements and IUPAC names of compound

Content

OXIDATION-REDUCTION (REDOX) REACTION

Chemical reaction are changes in which some new chemical substances are formed. The substances which undergo the chemical change are known as REACTANTS while the new substances formed are PRODUCTS.

TYPES OF CHEMICAL REACTION

Chemical reactions can be grouped in the following ways:

Combination reaction: This is when two or more substances combine to form a single compound. E.g

Cu  + O2                          CuO

Decomposition  reaction: This is when a single compound splitting up into two or more simpler substance. When heat is required the reaction is known as thermal decomposition e.g

2Pb(NO3)2(s)                            PbO + 4NO2   +  O2

Displacement reaction: in this type of reaction, one element (or radical) replaces another element (or radical) in a compound e.g  Zn    +  CuSO4                   ZnSO4  +    Cu    

Double decomposition: The reactants decomposes to form new substances by an exchange of radical

AgNO3(aq)     +   NaCl(aq)                 AgCl     +   NaNO3

Catalytic reaction: is a reaction which uses a catalyst

Reversible reaction: This is a reaction in which the direction of chemical change can be reversed e.g

A + B                   C  + D

Thermal dissociation: This is a reaction in which each molecule of a substance dissociates into two or more simpler molecules or atom on the application of heat. E.g NH4Cl                          NH3(g)    +     HCl(g).

Oxidation and Reduction reaction: This reaction that involves a simultaneous gain and loss of electrons.

DEFINITIONS OF OXIDATION AND REDUCTION

OXIDATION

There are four definition you can use for oxidation:

The gain / addition of oxygen:- Oxidation is simply a reaction in which oxygen combines with another substance.      CuO     +   H2                        Cu    +   H2O

ii.     Removal / loss of Hydrogen:- Oxidation is the removal of hydrogen from a compound.

         H2S(g)     +     Cl2(g)                        2HCl   + S

iii.    Addition of electronegative element:- Oxidation is the addition of electronegative elements and the removal of electropositive elements.

Ca    +   Cl2                      CaCl2

iv.  Loss of electron:-  Oxidation  is a process involving loss of electron.    2FeCl2(s)    +   Cl2(g)                   2FeCl3(s).

 

 

 

REDUCTION

There are four definition you can use to describe reduction:

The removal of oxygen:- Reduction is simply a reaction in which oxygen is removed from a  another substance.      3Fe     +   4H2O                        Fe3O4    +   4H2

ii.     Addition  of Hydrogen:- Reduction means addition  of hydrogen from a compound.

         H2S(g)     +     Cl2(g)                        2HCl   + S

iii.    Removal of electronegative element:- Reduction is the removal  of electronegative elements and the addition of electropositive elements.

Mg    +   Cl2                      MgCl2

In a reaction where two electronegative elements are present, the more electronegative of the two is regarded as the reduction.

F, O, Cl, N, Br, S, C, I, P

Electronegativities decrease

 H2S    +   Br2                      HBr2    +   S

iv.  Gain of electron:-  Reduction  is a process involving gain of electron.    2FeO(s)    +   O2(g)                   2Fe2O3(s).

OXIDATION NUMBERS AND IUPAC NAME

Rules for assigning oxidation numbers

Oxidation of free elements is zero e.g  K, Al, Cl, P4 etc

The oxidation number of a simple ion has the same size and sign as the charge of the ion e.g  K+, Mg2+, Al3+, Cl- , O2- are +1, +2, +3, -1, -2 respectively.

The algebraic sum of the oxidation number in the formula of a compound is zero e.g MgO.

Oxidation number of hydrogen is +1 except in hydrides where it is -1.

Oxidation number of oxygen in any compound is -2, except in peroxides where it is -1.

Examples 

1a. Calculate the oxidation numbers of (i) S in H2SO4 (ii) N in HNO3  (iii) Cl in KClO   (iv) Cr in Na2CrO4 (b) hence give their IUPAC names.

H2SO4 = 2H + S +4O

= 2(1) + S +4(-2)

=2 + S -8

= S -6

S       = 6

H2SO4 – Tetraoxosulphate(vi) acid

 HNO3 = H + N + 3O

= 1 + N + 3(-2)

= 1 + N -6

= N -5

N       = 5

HNO3 – Trioxonitrate (v) acid

iii.    KClO  = K + Cl + O

= 1 + Cl + (-2)

= Cl -1

= 1

KClO – Potassiumoxochlorate (i)

iv.  Na2CrO4  = 2Na + Cr + 4O

= 2(1) + Cr + 4(-2)

= 2 + Cr -8

= -6 + Cr

Cr       = 6

Na2CrO4 – Disodiumtetraoxochromate(vi)

PROCESSES WHERE CONCEPTS OF OXIDATION NUMBER IS APPLIED

In the IUPAC system of naming compounds

Balancing REDOX  equation

It identified which element in a compound is oxidized or reduced.

PRESENTATION

STEP I: The teacher explains reaction

STEP II: The teacher explains types of reaction

STEP III: The students chorus the types of reaction

STEP IV: The teacher defines oxidation and reduction

STEP V: The teacher leads the students to find the oxidation number of element in a compound

EVALUATION

The teacher evaluates the lessons by asking the following question

What is the differences between combination reaction and decomposition reaction.

  Define oxidation –reduction in terms of addition of oxygen and gain or loss of electrons

Calculate the oxidation number of S in SO2

  ASSIGNMENT

What is the oxidation number of  (i) Cl in KClO3 (ii) Xe in Ba2XeO6

 

Comments

  1. BinaryApril 27, 2021 at 9:29 PM

    Great job. This will go along way in assisting the teachers

    ReplyDelete

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