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Redox Reactions and Electrode Processes

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  • Last Updated : 10 Feb, 2022
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Redox reactions are oxidation-reduction chemical reactions in which the oxidation states of the reactants change. The term ‘redox’ refers to the reduction-oxidation process. All redox reactions can be divided down into two types of reactions: reduction and oxidation. In a redox reaction or Oxidation-Reduction process, the oxidation and reduction reactions always happen at the same time. The oxidising agent is the substance that is being reduced in a chemical process, while the reducing agent is the substance that is being oxidised.

Galvanic Cell/Voltaic Cell

A galvanic cell, also known as a Voltaic cell, is an electrochemical cell that generates electrical energy through a redox reaction or redox process.

A voltaic cell is made up of two half-cells that perform either the reduction or oxidation processes. The left and right half-cells are the two half-cells. A copper metal rod/strip dipped in copper (II) sulphate solution forms the right half-cell, while a zinc metal rod/strip dipped in zinc sulphate solution forms the left half-cell. The metal strips are called electrodes, and they serve as a conductor in the circuit. It aids in the transmission of electrons from the strips to the electrolyte solutions in which they are dipped.

The two electrodes in the diagram above are connected by a metal wire. The circuit is opened and closed with the use of a switch. The porous membrane that joins the two halves (half-cells) contributes to the circuit’s completion. Using a zinc-copper cell as an example is the best way to demonstrate the electrochemical process in a voltaic cell. So, let’s have a look at the zinc-copper redox process.

Redox Process (Oxidation & Reduction Reaction) of Zinc & Copper

The two electrodes in the diagram above are connected by a metal wire. The circuit is opened and closed with the use of a switch. The porous membrane that joins the two halves (half-cells) contributes to the circuit’s completion. Using a zinc-copper cell as an example is the best way to demonstrate the electrochemical process in a voltaic cell. So, let’s have a look at the zinc-copper redox process.

(Anode) Oxidation Half-Reaction

Zn(s) → Zn2++2e

(Cathode) Reduction Half-Reaction

Cu2++2e→ Cu(s)

To make metallic copper, zinc loses electrons that are grabbed by copper ions. The entire redox reaction between zinc and copper is:

Cu2++Zn(s) → Cu(s)+Zn2+

The Redox Process in Zinc and Copper Cells was observed.

Because zinc ranks higher in the activity series than copper and is oxidised more easily than copper, the zinc electrode serves as the anode in a galvanic cell.

Zn(s) → Zn2++2e

Because of the loss of zinc metal, the zinc anode gradually degrades, while the concentration of zinc ion grows owing to electron production at the anode.

The electron travels from the zinc anode to the copper electrode via the external wire, where it reacts with copper ions in the solution to generate metallic copper.

Cu2++2e→ Cu(s)

The reduction takes place in the cathode, which is a copper electrode. Due to the creation of copper metal, the mass of the cathode will increase, while the concentration of copper (II) ions will decrease.

The movement of ions across the membrane contributes to the cell’s neutrality.

Daniel Cell

An electrochemical/voltaic cell is the same as a Daniel cell. It is made up of a zinc rod that has been dipped in zinc sulphate solution and a copper rod that has been dipped in a copper sulphate solution. A salt bridge links the two solutions together. Two half-cells of zinc and copper will undergo oxidation and reduction to form a redox pair. The redox pair in Daniel cell is Zn2+/Zn and Cu2+/Cu.

In a redox pair, the substance undergoing oxidation and reduction is present. In a redox pair, a vertical line acts as a separator or interface between the oxidised and reduced forms. The interface can take the shape of a solid or a solution.

A salt bridge is just a U-shaped tube filled with potassium chloride or ammonium nitrate solution. Boiling the solution with agar-agar and cooling it until it has a jelly-like consistency solidifies it.

The electric contact between the solutions is established by the salt bridge. At the same time, it helps in solution separation. The copper and zinc rods are connected by a metallic wire, an ammeter, and a switch. Daniel Cell’s entire set-up is an illustration of his work. There is no reaction and no current flow when the switch is turned off. However, as soon as the switch is turned on, we can see the following.

Observations of Daniel Cell

The electronic transfer occurs over a metallic wire that runs between the rods. The flow of current is indicated by the direction of the arrow. The flow of electricity is caused by the passage of ions from one solution of the beaker to the other via the salt bridge. Current flow, on the other hand, is not possible until there is a potential difference between the two electrodes (copper and zinc rods).

At the electrodes, half-reactions have been seen. As a result, the anode is the electrode that undergoes oxidation, whereas the cathode undergoes reduction. The entire potential at each electrode is referred to as electrode potential.

Electrode Potential

In electrochemistry, the concept of electrode potential is crucial. It aids in the prediction and control of an electrochemical process’s direction and intensity (for example, corrosion).

Standard Electrode Potential

The potential difference between the metal and its solution is known as the electrode potential. If the concentration of the participating species in the electrode reaction is unity and the reaction occurs at 298K, the electrode potential is referred to as Standard Electrode Potential (E0).

The standard electrode potential (E0) of hydrogen gas, in the case of the convention, is 0.00 volts. The redox couple is a stronger reducing agent than the H+/H2 couple when the standard electrode potential is negative. On the other hand, a positive standard electrode potential suggests that the redox couple is a weaker reducing agent than the H+/H2 pair.

Calculation of Electrode Potential

The electrode potential can be calculated using the following formula:

Ecell = Ered–Eoxid

The half-cell with the larger reduction potential goes through the reduction process, whereas the half-cell with the lower reduction potential goes through the oxidation process.

Uses of Electrode Potential

  • It may be used to investigate processes like corrosion and pitting, as well as control the reaction process.
  • The Electrode Potential can be used to help choose materials and equipment for reaction control.
  • Corrosion caused by electrochemical and chemical reactions and processes can be predicted with this tool.

Sample Questions

Question 1:  What processes are involved in redox reactions?

Answer

A redox process is an electron transfer reaction that involves both reduction and oxidation, with reduction being the intake of electrons and oxidation being the release of electrons.

Question 2: How does a redox reaction produce electricity?

Answer

A galvanic cell, also known as a Voltaic cell, is an electrochemical cell that generates electrical energy through a redox reaction or redox process. A voltaic cell is made up of two half-cells that perform either the reduction or oxidation processes.

Question 3: How Electrolysis is an example of a redox reaction?

Answer 

Electrolysis is a redox reaction because reduction occurs at the cathode and oxidation occurs at the anode, and both of these reactions occur at the same time.

Question 4: What does the reduction process do?

Answer

Chemical entities lose electrons during the reduction process, lowering their oxidation number. The oxidation part of the reaction involves the loss of electrons. Reduction is the polar opposite of oxidation.

Cu2++2e→ Cu(s)

Question 5: What is a redox couple example?

Answer

In redox reactions, a redox pair is formed by the oxidised and reduced versions of each reactant. Redox couples are denoted as “Ox/red.” For example- Cu2+/Cu and Zn2+/Zn, have an oxidised version on the left and a reduced version on the right, separated by a slash.

Question 6: What are the uses of electrode potential?

Answer

  • It helps with corrosion and pitting investigations, as well as reaction control.
  • Electrode Potential can be used to help choose materials and equipment for reaction control.
  • Corrosion caused by electrochemical and chemical reactions and processes can be predicted with the help of this programme.

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