Rusting of Iron (Cambridge O Level Chemistry)

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Alexandra Brennan

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Rusting of Iron

  • Rust is a chemical reaction between iron, water and oxygen to form the compound hydrated iron(III) oxide (rust)
  • Oxygen and water must be present for rust to occur
  • During rusting, iron is oxidised 

iron +  water + oxygen  →  hydrated iron(III) oxide 

 Investigating rusting

  • To investigate the conditions required for rusting, prepare three test tubes as shown in the diagram
  • The oil in the 2nd tube keeps out air and the water has been boiled so that no air is left in it
  • The calcium chloride in the 3rd tube is used to remove any moisture in the air
  • After a few days, the iron nail in the 1st tube will be the only nail to show signs of rust

Conditions for rusting, IGCSE & GCSE Chemistry revision notesDiagram showing the requirements of oxygen and water for rust to occur: only the nail on the left rusts

Rust prevention methods

Barrier methods

  • Rust can be prevented by coating iron with barriers that prevent the iron from coming into contact with water and oxygen
  • However, if the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust

Barrier Methods of Rust Prevention table, IGCSE & GCSE Chemistry revision notes

Examiner Tip

Only iron or steel (an alloy made from iron) can rust. If any other metal oxidises in air causing the metal to break down, you should say that the metal has corroded.

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.