Summary note chemistry year 10
Here’s a summary note on Electrolysis for IGCSE Chemistry:
Electrolysis
Definition: Electrolysis is a process that uses an electric current to drive a non-spontaneous
chemical reaction, typically to decompose a compound into its elements.
--Key Components of Electrolysis:
1. Electrolyte: A molten or aqueous solution containing ions that can carry an electric current.
Examples include water (H₂O), sodium chloride (NaCl), and copper(II) sulfate (CuSO₄).
2. Electrodes: Two conductive materials (usually made of graphite or metal) that are immersed
in the electrolyte and connected to the power supply.
Anode: The positive electrode, where oxidation (loss of electrons) occurs.
Cathode: The negative electrode, where reduction (gain of electrons) occurs.
--Electrolysis of Molten Compounds:
1. Electrolysis of Molten Sodium Chloride (NaCl):
At the Anode: Chlorine gas (Cl₂) is produced by the oxidation of chloride ions (Cl⁻).
At the Cathode: Sodium metal (Na) is produced by the reduction of sodium ions (Na⁺).
Overall Reaction:
2. Electrolysis of Molten Lead(II) Bromide (PbBr₂):
At the Anode: Bromine gas (Br₂) is produced by the oxidation of bromide ions (Br⁻).
At the Cathode: Lead metal (Pb) is produced by the reduction of lead(II) ions (Pb²⁺).
Overall Reaction:
--Electrolysis of Aqueous Solutions:
In aqueous solutions, both the ions from the solute and water molecules contribute to the
reactions at the electrodes. The products depend on the relative reactivity of the ions.
1. Electrolysis of Copper(II) Sulfate (CuSO₄):
At the Anode: Copper is oxidized, and copper(II) ions (Cu²⁺) enter the solution.
At the Cathode: Copper(II) ions are reduced to form copper metal.
Overall Reaction:
2. Electrolysis of Sodium Chloride (NaCl) Solution:
At the Anode: Chlorine gas (Cl₂) is produced by the oxidation of chloride ions (Cl⁻).
At the Cathode: Hydrogen gas (H₂) is produced by the reduction of hydrogen ions (H⁺) from
water.
Overall Reaction:
--Factors Affecting Electrolysis:
1. Concentration of Ions: The concentration of the electrolyte affects the amount of product
formed at the electrodes.
2. Nature of the Electrodes: Inert electrodes (like graphite) do not participate in the reaction,
while active electrodes (like copper) may dissolve or participate in the reaction.
3. Voltage/Current: The voltage applied across the electrolyte influences the ease of electron
flow and thus the products formed.
--Uses of Electrolysis:
1. Extraction of Metals: Electrolysis is used to extract metals from their ores, especially for
reactive metals like aluminium (extracted from bauxite).
2. Electroplating: Deposition of a metal onto the surface of an object to improve appearance,
reduce corrosion, or provide conductivity (e.g., gold plating on jewelry).
3. Production of Chlorine and Sodium Hydroxide: Electrolysis of sodium chloride (brine)
produces chlorine gas, hydrogen gas, and sodium hydroxide.
4. Electrorefining: Purification of metals like copper.