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)