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Topic 12 Corrosion

Topic 12 Corrosion. Aim: To find out What is corrosion? What is required for corrosion to occur?. What is corrosion?. Corrosion is a chemical reaction which involves the surface of a metal changing from an element to a compound .

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Topic 12 Corrosion

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  1. Topic 12Corrosion • Aim: • To find out • What is corrosion? • What is required for corrosion to occur?

  2. What is corrosion? • Corrosion is a chemical reaction which involves the surface of a metal changing from an element to a compound. • Corrosion progressively weakens a metal and eventually destroys it. • Most metals corrode but different metals corrode at different rates.

  3. In general, the more reactive a metal, the faster it will corrode. • For example, • When sodium is cut it has a bright, shiny surface, but this becomes dull after a few seconds as the metal corrodes. Copper turns green over a number of years; corrosion is very slow. Gold does not corrode at all. • Corrosion is an example of oxidation; where the metal atoms lose electrons to form metal ions. Fresh metal with a shiny appearance  reacts with atmosphere  metal oxide.

  4. What conditions are needed for corrosion? Conclusion: In order for rusting to occur both oxygen (from the air) and water are required.

  5. Steel wool Water Which gas from the air is required for corrosion? Water rises approx 1/5 th of the way up the test tube. Oxygen is approx 20% of the air.  Oxygen is needed for rusting

  6. Chemical tests for products of rusting

  7. Conclusion: • Test for OH- ions: Ferroxyl indicator turn from pale yellow to pink • Test for Fe2+ ions: Ferroxyl indicator turns from pale yellow to blue • Test for Fe3+ ions: Ammonium thiocyanate turns from colourless to blood red. • Ferroxyl Indicator can be used to determine not only if rust is present but also the amount of rusting which has taken place. The more bluecolour there is, the more rustinghas taken place.

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