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Displacement Reactions
A displacement reaction occurs when a more reactive element displaces or removes a less reactive element from its compound. Pattern: A + BC → AC + B. Example: Iron displaces copper from copper sulphate solution.
More reactive element → Pushes out less reactive!
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Activity 1.9: Iron + Copper
When iron nails are dipped in blue copper sulphate solution, the blue color fades and the nails become brownish (copper coating). Iron (more reactive) displaces copper from CuSO₄, forming FeSO₄ (pale green) and metallic copper.
Fe + CuSO₄ → FeSO₄ + Cu (Brown coating!)
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Reactivity Series
The reactivity series ranks metals by their ability to displace other metals. More reactive metals (like Zn, Fe, Pb) can displace less reactive metals (like Cu, Ag, Au) from their compounds. Zinc and lead can both displace copper!
K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au
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Double Displacement
In double displacement reactions, ions of two compounds exchange places to form two new compounds. Pattern: AB + CD → AD + CB. Example: Sodium sulphate reacts with barium chloride to form barium sulphate and sodium chloride.
Ion exchange: Both compounds swap partners!
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Precipitation Reactions
When two solutions react and produce an insoluble solid (precipitate), it's a precipitation reaction. In Activity 1.10, mixing Na₂SO₄ and BaCl₂ produces white BaSO₄ precipitate that settles at the bottom. This is also a double displacement!
Precipitate = Insoluble solid formed in solution
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Applications
Displacement reactions are used in extracting metals from ores (metallurgy), electroplating, making alloys, and water treatment. Precipitation reactions are used in water purification, qualitative analysis, and producing pigments and medicines.
Chemistry powers metal extraction and purification!