Page 99 - Chemistry_Form_2

Chemistry
for Secondary Schools

Another example of a displacement reaction is when solid iron reacts with
copper(II) sulfate. In this reaction, iron displaces copper from copper(II) sulfate.

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Displacement reactions have various practical applications in real life across
different industries and fields. Here are a few examples:

(a) Extraction of metals: More reactive metals displace less reactive metals
from their compounds. For example, iron is extracted from its ore (iron(III)
oxide) using aluminium:

This is a highly exothermic reaction and is used in welding, like in railway
tracks.

(b) Purification of metals: Less reactive metals are displaced from their solutions
by more reactive metals. For example, impure silver is purified by displacing
it with a more reactive metal, such as copper.

(c) Rust prevention: In rust prevention treatments, displacement reactions are
involved through a principle called sacrificial protection. A more reactive
metal like zinc is coated onto iron or steel. When both are exposed to air and
moisture, zinc reacts (oxidises) first, sacrificing itself to protect the iron from
rust. During the process, zinc acts as a sacrificial anode, forming a protective
layer of zinc. This is called galvanisation.

(d) Treatment of wastewater. Metals like aluminium or zinc displace harmful
substances or ions from wastewater. For example, zinc is used to remove
copper ions from industrial waste solutions.

The copper metal is easily recovered as solids from wastewater.

Precipitation reactions
A precipitation reaction is a chemical reaction in which two soluble substances
(typically in aqueous solution) combine to give a soluble substance and an
insoluble substance known as a precipitate. This reaction is expressed in the
general form of:

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 92 01/08/2025 11:20:59