METAL REACTIVITY SERIES AND DISPLACEMENT REACTIONS 2

As a follow on form the previous post here is a bit more info...

DISPLACEMENT REACTION IN SOLUTION
A more reactive metal will displace a metal from it's compound in solution.
Observations could include:

• the more reactive metal gradually dissolves
• the less reactive metal coats the more reactive metal
• the solution may change colour
• theat is given out because these reactions are exothermic
• fizzing may occur

Here are two examples of these reactions:

1. Magnesium and Copper Sulphate solution

Magnesium is more reactive than Copper so it displaces Copper from the Copper Sulphate Solution.

The Word equation is:

Magnesium + Copper Sulphate

---------> Magnesium Sulphate + Copper

The Magnesium has been coated with Copper in this displacement reaction

2. Iron and Copper Sulphate Solution

Iron is more reactive than Copper so it displaces the Copper from the Copper Sulphate Solution.

The word equation for this reaction is:

Iron + Copper Sulphate

------------> Iron Sulphate + Copper

The Iron becomes coated with Copper in this displacement reaction

However the rate of this reaction is much slower (it takes much longer) as Iron and Copper are much closer together in the Reactivity Series

Metal                           Compound in Solution

                                     MgSo4            CuSo4            FeSo4

Mg                               No                    Yes                 Yes                             

Cu                                No                     No                 No

Fe                                No                      Yes                No

• 
  
  A metal will not react with it's compound
• 
  
  Magnesium is the most reactive of the three because it reacted with the other two metals
• 
  
  Copper is the least reactive because it didn't react with compounds of  the other two metals
• 
  
  Note that the compound itself is not important, only the metal it contains, so Copper Nitrate, for example, would give the same answer as Copper Sulphate

Displacement reactions also occur with solid metal oxides, but that is for another post.

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METAL REACTIVITY AND DISPLACEMENT REACTIONS

 This post should help with Year 11PY internal assessment 1.1

The reactivity series to the side shows a list of metals, with the addition of two non metals: carbon and hydrogen, arranged in order of their reactivity from most reactive to least reactive.By using the reactivity series we can predict what will happen in displacement reactions. The reason carbon and hydrogen are included in this list is because carbon is used in the extraction of iron ore and any metals below hydrogen in the list will not react with dilute HCl.


Metals react by losing electrons which is oxidation; metals are the reductant, ie they donate electrons.

When metals react with other other metals in a metal salt solution a displacement reaction takes place; a more reactive metal will take the place of a less reactive metal. In other words the more reactive metal donates electrons to the less reactive metal (existing in ion form).


The key point is that if a less reactive metal is added to a metal salt solution which contains metal ions from a more reactive metal then there will be no displacement and no reaction will take place. Therefore if we put Copper, Lead, Zinc, Aluminium into a solution of Magnesium Sulphate as Magnesium is more reactive there will be no reaction and nothing to observe as the Magnesium 'wins the competition' for the Sulphate ions.


Other Metal Salts that can be used are Nitrates and Chlorides for example.


In the practical carried out another example may help in consolidating knowledge. If we take Zinc and a solution containing Copper ions, in this case Copper Sulphate what is going to happen?

• Looking at the reactivity series above it can be seen that Zinc is more reactive than Copper
• Zinc being more reactive forces the Copper ions to accept electrons, ie Zinc acts as a reductant by donating electrons to the Copper ions in solution, which become Copper metal atoms
• Zinc then accepts the Sulphate ions and becomes oxidised and becomes Zinc Sulphate
• The Zinc metal will discolour and the blue Copper Sulphate solution fades in colour
• We can say that Zinc has displaced the Copper ions from the Copper Sulphate solution

 If we discount the spectator ions (Sulphate ions) the ionic equations are:

• Zn -----------------> Zn2+ + 2e
• C2+ + 2e ----------------> Cu

Using this information and the reactivity series you should be able to work out what metals will displace other metal ions from a metal salt solution