Embedded Files
Syllabus
Syllabus
A more reactive metal can displace a less reactive metal from a compound.
Oxidation is the loss of electrons and reduction is the gain of electrons.
Student should be able to:
write ionic equations for displacement reactions
identify in a given reaction, symbol equation or half equation the species oxidised and reduced.
What does this mean?
What does this mean?
What's the use of displacement reactions?
What's the use of displacement reactions?
It's possible to get a good idea how reactive most metals are by looking at the speed of their reactions with Water, dilute acids and Oxygen.
But there are 80 metals and many have very similar reactivity.
And some, like Aluminium, appear to be much less reactive than they actually are.
Displacement Reactions are the only way to be sure where to put similar metals on the series
Displacement
Displacement
So, it's hard to be sure until we carry out Displacement Reactions.
The more reactive a metal is, the stronger it bonds to other elements.
If we have a compound of an unreactive metal, like Copper Oxide, the Copper is only weakly held to the Oxygen.
If we mixed in a more reactive metal such as Iron and heated the mixture the Oxygen will move from the Copper that hold it weakly and to the Iron where it will be held more strongly.
Copper Oxide + Iron --> Iron Oxide + Copper
The Copper has been displaced by the Iron - the same would happen if we dropped an Iron nail into Copper Sulphate solution.
Copper will appear on the nail, and the solution will become less blue as the Copper is removed. Eventually it would turn brown as Iron Sulphate solution is created.
Copper Sulphate + Iron --> Iron Sulphate + Copper
So, if we wish to see how reactive two similar metals are, such as Iron and Zinc, we could make solutions of Iron Sulphate and Zinc Sulphate. We would add Iron to the Zinc Sulphate, and Zinc to the Iron Sulphate and watch for signs of a change.
This iron nail has displaced Copper from Copper Sulphate solution
Zinc Sulphate + Iron --> No reaction
Iron Sulphate + Zinc --> Zinc Sulphate + Iron
So Zinc is more reactive than Iron.
We could do the same with a range of metals.
And we would find that Aluminium displaces many metals that react better with Oxygen and water than it does.
Aluminium's reactivity is higher than simple experiments would suggest.
Redox
Redox
When Iron displaces Copper ions from solution there is an exchange of electrons.
The Iron atoms loses electrons to become positive ions - they have been Oxidised.
Fe(s) --> Fe3+(aq) + 3 electrons -
The Copper ions gain these electrons and are Reduced back to Copper atoms.
Cu2+(aq) + 2 electrons - --> Cu(s)
Reduction and Oxidation happen at the same time so we call this a RedOx reaction.
We could say that the Iron has reduced the Copper - the Iron is a Reducing agent.
Or that Copper has Oxidised Iron - making Copper the Oxidising agent.
Generally, whatever is oxidised is the reducing agent (and vice versa).
The most reactive metal always ends up being oxidised to an ion.
So the most reactive metals make the best Reducing agents.
The most unreactive metals make the best Oxidising agents.
Videos
Videos
PAST PAPER QUESTIONS
PAST PAPER QUESTIONS
2021
2018
Page updated
Google Sites
Report abuse