Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because
- zinc is lighter than iron
- zinc has lower melting point than iron
- zinc has lower negative electrode potential than iron
- zinc has higher negative electrode potential than iron
The Correct Option is D
Solution and Explanation
Electrochemical Series and Corrosion Protection
The standard reduction potentials for zinc and iron are given as:
\(E^{0}_{\text{Zn}^{2+}/\text{Zn}} = - 0.76 \, \text{V}\)
\(E^{0}_{\text{Fe}^{2+}/\text{Fe}} = - 0.76 \, \text{V}\)
Explanation:
Both zinc and iron have the same standard reduction potential of -0.76 V. However, zinc has a higher negative standard reduction potential (SRP), which means that zinc is more readily oxidized than iron. Therefore, in an electrochemical cell or corrosion process:
- Zinc (Zn) acts as the anode where it gets oxidized to zinc ions (\( \text{Zn}^{2+} \)) and loses electrons.
- Iron (Fe) acts as the cathode, where the electrons from zinc are accepted, and iron is protected from corrosion.
Thus, zinc protects iron by sacrificially oxidizing itself, making it a useful material for galvanizing or protecting iron surfaces from rusting.
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Concepts Used:
Electrochemical Cells
An electrochemical cell is a device that is used to create electrical energy through the chemical reactions which are involved in it. The electrical energy supplied to electrochemical cells is used to smooth the chemical reactions. In the electrochemical cell, the involved devices have the ability to convert the chemical energy to electrical energy or vice-versa.
Classification of Electrochemical Cell:
Cathode
- Denoted by a positive sign since electrons are consumed here
- A reduction reaction occurs in the cathode of an electrochemical cell
- Electrons move into the cathode
Anode
- Denoted by a negative sign since electrons are liberated here
- An oxidation reaction occurs here
- Electrons move out of the anode
Types of Electrochemical Cells:
Galvanic cells (also known as Voltaic cells)
- Chemical energy is transformed into electrical energy.
- The redox reactions are spontaneous in nature.
- The anode is negatively charged and the cathode is positively charged.
- The electrons originate from the species that undergo oxidation.
Electrolytic cells
- Electrical energy is transformed into chemical energy.
- The redox reactions are non-spontaneous.
- These cells are positively charged anode and negatively charged cathode.
- Electrons originate from an external source.