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Displacement Reactions
Displacement Reactions
• Lets look at the reaction between chlorine and potassium bromide
• When chlorine is bubbled through potassium bromide solution (colourless), the liquid turns red-brown, because bromine forms.
• The reaction is:
Cl2(g) Br2(g)2KBr(aq) 2KCl(aq)
Displacement Reactions
• Bromine has given up electrons to chlorine.• The bromine has been oxidized and the
chlorine has been reduced.• The Ionic Equation is:
Cl2(g) 2Br -(aq) 2Cl -
(aq) Br2(g)
Displacement Reactions
• In effect chlorine has pushed bromine out of the potassium compound and taken its place.
• It has displaced bromine.• Redox reactions like these, where one
element displaces another from a dissolved compound (solution), are called displacement reactions.
Displacement of One Metal by Another.
• An iron nail is placed in copper II sulfate solution.
• Soon copper appears on the nail and the solution turns green.
• Here iron and copper are competing to be the compound in solution. Iron wins.
• It displaces copper from copper II sulfate solution. A green iron II sulfate solution is formed.
The Equation
Fe(s) Cu(s)CuSO4(aq) FeSO4(aq)
Blue Green
• the ionic equation is:
Fe(s) Cu(s)Cu 2+(aq) Fe2+
(aq)
Displacement Reactions
• Other metals displace less reactive metals in the same way.
• A metal will always displace a less reactive metal from solutions of its compounds.
• When copper wire is placed in silver nitrate solution, the solution turns blue and crystals of silver form on the wire.
• Which metal is more reactive?
Remember the Activity Series
• Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > (hydrogen) > Copper > Silver > Gold
• Copper is more reactive.
Cu(s) Ag(s)AgNO3(aq) Cu(NO3)2(aq)
Try This….
• What would you see if you added zinc to copper sulfate solution?
• Hint zinc sulfate is colourless.
Now Try This……
• Tin does not react with iron II oxide. But it reduces lead II oxide to lead.
• Arrange tin, iron and lead in order of decreasing reactivity.
• Iron > tin > lead
Displacement of Hydrogen
• Some metals will react with dilute acid.• These metals displace Hydrogen from the acid.
Mg(s) H2(g)HCl(aq) MgCl2(aq)