OXIDATION AND REDUCTION REACTIONS.

OXIDATION AND REDUCTION REACTIONS.

Oxidation and reduction is an important topic for understanding chemistry. It serves as the foundation for building knowledge on  the behavior of metals, nonmetals,organic chemistry and general periodic table characteristics.

The definition of oxidation and reduction has different meanings based on different terms. The following terms for the definition of reduction and oxidation includes the following

1.       Addition of oxygen

2.       Removal of hydrogen

3.       Addition of electronegative element

4.       Addition and Removal of electrons

ADDITION OF OXYGEN

The addition of oxygen to a substance is known as oxidation. Because oxygen is one of the earlier know reactive elements. So when it combine with substances, the substances were said to be oxidized because oxygen was added to it. Consequently, since oxidation and reduction tend to occur at the same time.  For instance during the combustion of coal to form carbon dioxide,

C_(s) + O_{2 (g)} => CO_{2 (g)}

We can see that oxygen combines directly with carbon, hence carbon is oxidized. So we can say that in terms of carbon, oxidation has occurred.

Since oxidation is the addition of oxygen, reduction is the removal of oxygen

 C(s) + 2ZnO(g) => CO2(g) + 2Zn(s)

Carbon is oxidized to carbon(IV) oxide, Zinc Oxide is reduced to Zinc.

REMOVAL OF HYDROGEN

Hydrogen is result displaced by most metals in reactions.In terms of hydrogen, oxidation is defined as the removal of hydrogen while reduction defined as the addition of hydrogen.

H₂S_(s) + Cl_{2 (g)} => 2HCl _(g) + S_(s)

Hydrogen sulphide was reduced to sulphur, because of the removal of hydrogen. This means that oxidation has occurred. The oxidizing agent is chlorine. Consequently, addition of hydrogen to chlorine is reduction while the chlorine is the reducing agent.

ADDITION OF ELECTRONEGATIVE ELEMENTS

Oxidation is a term whiy originate from oxygen. Hence oxygen is a very electronegative element. Hence like other electronegative elements we can refer a definition for oxidation and reduction. Oxidation in term of electronegative element means the addition of electronegative element, or the removal of electropositive elements. This similar previous definition of oxidation and reduction in terms of addition and removal of oxygen, since oxygen is an electronegative element. Also the term electronegative or electropositive is not an absolute term, but rather a comparative term used to describe how two element are powerful when compared to one another.

Generally, metals are electron donors which means that they undergo oxidation and are good reducing agents, while non-metals are electron acceptors as they undergo reduction which make them good oxidizing agent. However, there tend to be differences in the power of their electropositivty and electronegativity. This idea of relative electronegativity or electropositivity lead us to the arrangement of elements based on their level of negativity or positivity. This arrangement is known as the electrochemical series.

The electrochemical series (ECS) helps us understand the general behavior of elements with one another regardless of whether they are metal/metal, non-metal/metal or non-metal/nonmetal reaction.

                                                   

Decreasing electropositivity for metals                           Increasing electronegativity of non metals

ADDITION AND REMOVAL OF ELECTRONS

Oxidation is defined as the loss of electrons while reduction is described as the gain of electrons. Metals undergo oxidation easily, while.non metals undergo reduction easily In reactions it is important to take note of which element is gaining electron and which element is losing electrons in order to be able to attribute which is undergoing oxidation or reduction.

 For instance in the reaction below

MnO_2(s) + 4HCl_(g) => MnCl_2(s) + 2H₂O_(l) + Cl_2(g)

Manganese (IV) oxide is oxidized to manganese (II) chloride. This implies a change in the oxidation number of manganese from +4 to +2, indicating that there was a gain of two electron by manganese(reduction), while the chloride ions from hydrochloric acid was lost electrons to become chlorine gas(oxidation).The manganese(IV)oxide is the oxidizing agent while the chloride ion is the reducing agent. A good of looking at this is to be able to calculate` the oxidation number of the element in the compound involved.

Another example is the reaction involving the reduction of heptaoxochromate (IV) to chromium (iii) when sulphur (iv) oxide is oxidized to tetraoxosulphate (iv) acid.

Cr₂O₇^2- + SO₂ => 2Cr³⁺ + SO₄^2-

We can clearly see that the oxidation number  of chromium changes from +6 to +3.This indicates a gain of 3 electrons while the that of sulphur changes from +4 to +6 which indicates a loss of electron. We can say that chromium was reduced while sulphur was oxidized. Hence chromium in the equation is good oxidizing agent while sulphur is a good reducing agent.