Displacement Reactions By the end of this lesson I should be able to: 1.Use the Electrochemical series to explain why displacement reactions occur and describe the experimental observations. 2.State that reactions of metals with acids can establish the position of hydrogen in an electrochemical series. 3.State that the reactions of metals with acids can establish the position of hydrogen in an Electrochemical series.

Displacement Reactions Aim: To investigate which metals can displace other metals from solution. Method:

Results: Sodium sulphate Zinc sulphate Copper (II) sulphate Silver nitrate Row 1 Magnesium Row 2 Tin Row 3 Copper

The following are examples of DISPLACEMENT REACTIONS. 1.Mg(s) + Cu 2+ SO 4 2- (aq)  Mg 2+ SO 4 2- (aq) + Cu(s) 2.Zn(s) + Cu 2+ SO 4 2- (aq)  Zn 2+ SO 4 2- (aq) + Cu(s) 3.Mg(s) + Zn 2+ SO 4 2- (aq)  Mg 2+ SO 4 2- (aq) + Zn(s) Metals higher in the ECS ‘push out’ metals lower from solution, taking their place.

Explanation of Displacement Reactions If piece of zinc metal is added to a solution of copper (II) sulphate, the zinc slowly becomes smaller and a brown solid covers it. At the same time the blue copper (II) sulphate solution loses its colour. The zinc atoms have LOST electrons and turned into zinc ions, which go into solution.

The copper ions GAIN the electrons lost by the zinc and turn into copper metal atoms. This is called a DISPLACEMENT REACTION and the overall reaction can be represented by;

As a general rule, a metal will displace a metal lower than itself in the ECS. e.g.- iron would displace silver ions from a solution of silver nitrate as iron is above silver in the ECS. –lead would not displace tin ions from a solution of tin chloride as lead is lower than tin in the ECS. DISPLACEMENT REACTION: Formation of a metal from a solution containing its own ions when a metal higher than itself in the electrochemical series is added to it.

Hydrogen in the ECS Hydrogen and other non-metals are also in the ECS. Considering the reactions of metals with dilute acids (contain H + ) Metals down to lead in the ECS react with dilute acids to produce hydrogen gas, i.e. they displace hydrogen ions from acids. This is an example of a displacement reaction.

e.g. Mg(s) + 2H + Cl - (aq)  MgCl 2 + H 2 2H + + 2e -  H 2 So hydrogen can be placed below lead but above copper in the ECS. Metals below hydrogen in ECS will not react to displace hydrogen.

Question 1. For the following experiments decide whether or not a reaction takes place and if so write a balanced chemical equation for the reaction. a) Magnesium added to iron (II) sulphate solution b) Zinc added to silver (I) nitrate solution c) Iron added to tin (II) chloride solution d) Nickel added to aluminium chloride solution

Answers a)Mg(s) + Fe 2+ SO 4 2- (aq)  Mg 2+ SO 4 2- (aq) + Fe(s) b)Zn(s) + 2Ag + NO 3 - (aq)  Zn 2+ (NO 3 - ) 2 + 2Ag(s) c)Fe(s) + Sn 2+ (Cl - ) 2 (aq)  Fe 2+ SO 4 2- (aq) + Sn(s) d) No reaction

Spectator Ions Consider: Mg(s) + Cu 2+ SO 4 2- (aq)  Mg 2+ SO 4 2- (aq) +Cu(s) Remove spectator ion (SO 4 2- ) Mg(s) + Cu 2+ (aq)  Mg 2+ (aq) + Cu(s) Ion electron equations Mg(s)  Mg 2+ (aq) + 2e - Cu 2+ (aq) + 2e -  Cu(s)

From the ion-electron equations we can see that Mg is losing electrons to form a compound and Cu2+ is gaining electrons to form an element. Mg is oxidised. Cu2+ is reduced.