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Chemistry · Class 9 · Chapter 7: Electrochemistry

8 min

Key points

Electrochemistry is the branch of chemistry that deals with the relationship between electrical energy and chemical energy
Electrolysis is the process in which electrical energy is used to bring about a non-spontaneous chemical reaction
An electrolyte is a substance that conducts electricity when dissolved in water or when melted
Strong electrolytes completely ionize in solution while weak electrolytes partially ionize
Electroplating is the process of depositing a thin layer of metal on another metal by electrolysis
Galvanic cells convert chemical energy into electrical energy spontaneously
The anode is the electrode where oxidation occurs and cathode is where reduction occurs
Faraday's laws relate the amount of substance deposited to the quantity of electricity passed
Applications include electroplating of jewelry in Karachi's markets and purification of copper

Definitions

Electrolysis: The process in which electrical energy is used to bring about a non-spontaneous chemical reaction
Electrolyte: A substance that conducts electricity when dissolved in water or when melted due to the presence of mobile ions
Electroplating: The process of depositing a thin layer of one metal on the surface of another metal by means of electrolysis
Galvanic Cell: An electrochemical cell that converts chemical energy into electrical energy by means of spontaneous redox reactions
Faraday: The quantity of electricity required to deposit or liberate one gram equivalent of any substance during electrolysis, equal to 96,500 coulombs

Worked example

Define electrochemistry and explain the process of electrolysis of water. (5 marks)

Electrochemistry is the branch of chemistry that deals with the study of chemical reactions involving electric current. Electrolysis is the process of decomposition of an electrolyte by passing electric current through it. In electrolysis of water, dilute sulphuric acid is added to make water conducting. At cathode (negative electrode): 2H⁺ + 2e⁻ → H₂. At anode (positive electrode): 4OH⁻ → 2H₂O + O₂ + 4e⁻. Hydrogen gas is produced at cathode and oxygen gas at anode in 2:1 ratio.

Common mistakes

Students confuse anode with cathode - remember Anode = oxidation, Cathode = reduction
Writing wrong electrode reactions - always check charge balance
Forgetting to draw proper electrolysis setup diagram with electrodes labeled
Mixing up strong and weak electrolytes - degree of ionization is the key difference
Not converting time to seconds in Faraday's law calculations

Quick recap

Electrochemistry studies chemical reactions involving electric current. Electrolysis decomposes electrolytes using electricity - anode is positive, cathode is negative. Galvanic cells generate electricity from chemical reactions - anode is negative, cathode is positive. Key applications include electroplating, industrial metal extraction, and battery technology.

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