Redox Reactions And Electrode Potential

Redox Reactions

Redox Reactions and Electrode Potential

What is a Redox reaction?

The term redox comes from two concepts which are involved in electron transfer: reduction and oxidation. Redox reactions are reactions in which reduction and oxidation reactions occur simultaneously. Oxidation reaction and reduction reaction are complementary to each other and always occur together. They involve the transfer of electrons between chemical species. The chemical species from which the electrons are removed are said to be oxidized and the reaction is termed as oxidation. Whereas addition of electrons to a chemical species is termed as reduction and the species is said to be reduced.

  • Oxidation is basically a rise in the oxidation state of molecules, ions and/or atoms and it also implies the loss of electrons.
  • The gain of electrons and decrease in the oxidation state of molecules, atoms and/or ions is called reduction.

Redox reactions are very similar to acid-base reactions, like acid-base reactions, redox reactions are also the matched sets that are both oxidation, as well as reduction, occurring simultaneously. If oxidation and reduction reaction do not occur simultaneously then it is called as a half-reaction.

Oxidation:

The word oxidation was first used to explain the addition of oxygen to an element. Elements commonly occur in the form of their oxides due to the presence of dioxygen in the atmosphere. With the help of the following reaction we can explain many other reactions:

\( S + O_2 \rightarrow SO_2\)

In this reaction, we can see that Sulphur is getting oxidized due to the addition of oxygen to it.

Oxidation can also be termed as the process of addition of oxygen to a substance or removal of hydrogen from a substance. Similarly, Reduction is defined as removal of oxygen from a substance or addition of hydrogen to a substance.

Reduction:

Similar to oxidation, Reduction is defined as the removal of oxygen from a substance or addition of hydrogen to a substance.

According to the definition, let us have a look at some examples:

\( 2HgO \rightarrow 2Hg + O_2 \)

This example proceeds with the removal of oxygen from mercuric oxide and hence is a Reduction reaction.

There are some reactions in which we can find that both the reactions take place simultaneously; these reactions are termed as redox reactions.

Redox reactions are not always associated with addition/removal of Oxygen/Hydrogen. Technically the oxidation state of the element increases and in a reduction reaction, it decreases. Examples of Redox Reaction:

Examples of Redox Reaction:

\( MnO_4^- + I^- \rightarrow Mn^{2+} + I_2\)

In this reaction, we can easily identify the element being reduced and oxidized respectively. Here Manganese (Mn) is the element being reduced (from +7 to +2); as it is being reduced, it is considered as an oxidizing agent. Iodine is the element that is being oxidized (-1 to 0) and hence, is considered as reducing agent.

Redox Reaction Of Zinc & Copper

Let us take an experiment in which zinc rod is oxidized to \(Zn^{2+}\) ions and copper ions are reduced to metallic copper because of the direct transfer of electrons. We take a solution of copper sulphate in a beaker and put the copper rod in it and in a second beaker we take zinc sulphate solution and put zinc rod in that. The copper rod and the zinc rod are connected externally so as to complete the electrical circuit and allow the transfer of electrons. The following half-reactions take place:

\(Zn ~(s)~ \rightarrow~Zn^{2+}~ +~ 2e^{-}\) [Oxidation half reaction]
\(Cu^{2+}~ + ~2e^{–} \rightarrow~Cu(s)\) [Reduction half reaction]

The electrons lost by solid zinc is gained by copper ions to form metallic copper. Zinc is getting oxidized while copper is getting reduced.

The overall redox reaction will be as follows:

\(Cu^{2+}~+~Zn ~(s)~\rightarrow~Cu~(s)~ +~ Zn^{2+}\)

Electrode Potential

From the above example, the half-reactions occur at electrodes. The electrode at which oxidation takes place is known as the anode, while the electrode at which reduction takes place is called the cathode.
Electrode potential is the overall potential associated with each electrode. Standard electrode potential is the potential of an electrode when the concentration of the reacting species is unity and the reaction takes place at 298K.

Uses Of Electrode Potential:

  • Helps the study of crevice corrosion and pitting, electrode potential in crevices and pits is studied for controlling reactions
  • Used for choosing substances and devices for controlling reactions
  • Prediction of corrosion-related chemical or electrochemical reactions

Click here to know about Application of Redox Reactions.


Practise This Question

Oxidation state of O in OF2 Is