Metals as reducing agents
The thermit reaction.
Mend a track
A cracked railway track needs to be joined.
How might hot molten iron be made right at the spot?
What this lesson covers
The idea
Highly reactive metals act as reducing agents by displacing less reactive metals from their compounds; these reactions are so exothermic that the metal is produced molten, and the reaction of iron(III) oxide with aluminium is the thermit reaction.
Mend a track
A cracked railway track needs to be joined.
How might hot molten iron be made right at the spot?
- By a reaction between iron(III) oxide and aluminium
- By melting rubber
- By adding cold water
Displacing with aluminium
Press Next step.
Heat from displacement
Besides carbon, highly reactive metals can serve as reducing agents, because they displace less reactive metals from their compounds. These displacement reactions are highly exothermic, so much heat is given out that the metal is produced molten. The reaction of iron(III) oxide with aluminium is the thermit reaction.
Highly reactive metals act as reducing agents by displacing less reactive metals from their compounds; these reactions are so exothermic that the metal is produced molten, and the reaction of iron(III) oxide with aluminium is the thermit reaction.
Notes
Highly reactive metals are reducing agents (they displace less reactive metals); the heat makes the metal molten; Fe₂O₃ + Al is the thermit reaction.
Check yourself
Which of these highly reactive metals is used as a reducing agent in the book's example?
Why is the metal produced in the molten state in these reactions?
The reaction of iron(III) oxide with aluminium is called ...
The thermit reaction is used to ...
- Gold. Gold is the least reactive metal in the series, so it cannot displace others.
- Silver. The book names highly reactive metals such as sodium, calcium and aluminium as reducing agents; silver is low in the series.
- Aluminium — correct. Yes!
- The displacement reactions are highly exothermic — correct. Yes!
- The metals are cooled strongly. The reactions give out a large amount of heat, so the metal is molten.
- Water is added. The molten state is due to the large amount of heat evolved.
- roasting. Roasting is heating sulphide ores strongly in excess air.
- the thermit reaction — correct. Yes!
- anodising. Anodising makes a thick oxide layer on aluminium.
- make aqua regia. Aqua regia is a mixture of two concentrated acids.
- colour aluminium articles. Dyeing the oxide layer is done after anodising.
- join railway tracks or cracked machine parts — correct. Yes!