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Practicals

Thermite Reaction
AKA: Thermit Reaction

Summary

Iron oxide is reduced by aluminium, producing an impressive reaction.

Operation

The thermite reaction is a well known and often conducted demonstration most teachers will be aware of. During the violent fiery reaction, iron oxide is reduced by aluminium, showing that aluminium resides above iron in the reactivity series.

Technicians will probably have to set up this equipment in advance and it is very important that the recipe is followed precisely and care taken when assembling the components. If your school has not conducted this demonstration before, it may be worth doing a test run so you are aware of the size and scale of the reaction.

Equipment required (per demonstration):

  • Bucket of sand
  • Fireclay crucible
  • Heat proof mats
  • Large safety screens (several if possible)
  • Long taper candle
  • Matches
  • Crucible tongs
  • Iron (III) oxide, dry powder, 15g
  • Aluminium powder, 5g, (HIGHLY FLAMMABLE)
  • Barium peroxide, 1.7g, (OXIDISING, HARMFUL)
  • Magnesium ribbon, 25cm, (LOW HAZARD)
  • Magnesium powder, 0.2g, (HIGHLY FLAMMABLE)

Ensure the Iron (III) oxide is completely dry before use by by heating in an evaporating dish over a Bunsen flame, then allowed to cool. NEVER attempt to dry the thermite mixture by heating.

The iron (III) oxide and the aluminium powder are mixed together by pouring back and forth between two separate sheets of paper and transferred to the fireclay crucible. Use a pencil to make a small cavity in the centre of the mixture.

The barium peroxide and the magnesium powder are mixed in the same fashion and poured into the cavity made by the pencil.

The magnesium ribbon should be inserted into the mixture leaving the free end to lean over the crucible edge.

The crucible should be placed in the centre of the sand bucket deeply so that it is stable. The bucket should be placed on several heat proof mats and safety screens assembled around the apparatus.

Soon after the magnesium ribbon is lit, the mixture will react violently and when cooled, a small bead of iron should be visible in the crucible.

The reaction which takes place is as follows:

Iron oxide + aluminium → aluminium oxide + iron

An alternative method for the thermite reaction over water, is given in the CLEAPSS L195 Safer chemicals, safer reactions. Only use the chemicals listed on this page in the amounts given and before conducting this demonstration, consult CLEAPSS or SSERC guidelines.

A full recipe and procedure can be found at www.practicalchemistry.org and further notes can be found from the CLEAPSS CD-ROM or on their website.

Safety

 Caution

Everyone witnessing this demo should wear eye protection and should be behind a safety screen.

The contents of this page are for information only. Please refer to CLEAPSS, SSERC or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.