Term 3

• Iron and steel are shiny grey solids. Iron is a pure metal, whereas steel is a mixture of the metal iron and the non-metal carbon. Steel is said to be an alloy – a mixture containing a metal and at least one other element.
• When iron or steel change to rust they become very weak as rust breaks up easily and this robs the iron and steel of the property we need.
• Method for The rusting experiment:

  1. Take 6 test tubes.
  2. In the first tube stand an iron nail in the air, with no added chemicals (control).
  3. In the second test tube place a few pieces of anhydrous calcium chloride in the tube followed by an iron nail. Stopper the tube. Label this TUBE 1.
  4. In the third tube place an iron nail and some tap water.

  
• What is the nail in contact with and does it rust?

  Air: no

  Dry air: no

  Water and air: yes

  Boiled water only: yes

  Air and salt solution: yes

  Zinc metal, water and air: no
• What does the drying agent (anhydrous calcium chloride) do?

  It absorbs water
• Why should the test tube  be stoppered with a bung in the rusting experiment ?

  To prevent water vapour from entering
• 1. Why was the water boiled in test tube D? (in the rusting experiment)

  To remove oxygen
• Why was oil added to one of the test tubes in the rusting experiment?

  To prevent oxygen from entering
•  What does the experiment tell us about rusting and how it can be prevented?

  For the rust to occur oxygen or air or water must be present, so you must prevent both
• Corrosion is the formation of a metal oxide on the surface of the metal. Rusting is the corrosion of iron and steel.
• A physical barrier is something put on the surface of the iron to stop it coming into contact with air and water
• Sacrificial protection is having the iron in contact with a more reactive metal, which corrodes first.
• 1. The two substances needed for rusting of iron and steel to occur are: oxygen/air and water
• The word equation for rusting is:

    iron  +  oxygen  +  water  → hydrated ironIII oxide 
• Salting roads has the effect of: speeding up the rusting of cars
• Two ways of protecting cars against rusting are:   

       painting/oiling/electroplating/galvanising
• Rusting destroys iron and steel by turning them into the compound hydrated Iron (III) Oxide, which is commonly known as rust.
• Rust is a soft, flaky reddish brown solid and so the iron loses its strength as a result of the chemical change.
• Most methods involve putting a PHYSICAL BARRIER  between the iron and the air. These include:

  1.  Painting

     2. Oiling 

  3. Greasing

       4. Covering with plastic

  5. Electroplating
• Sacrificial Protection is a very special way of protecting iron and steel. Explain how this method works.

  A more reactive metal makes contact with the iron (either directly or via a connecting wire). This metal corrodes first and prevents the iron from rusting.
• Explain how an iron / steel object is galvanised and how this method protects against rusting.

  Iron is dipped into molten zinc, which then solidifies on the surface forming a physical barrier to air and water. If the surface layer of zinc is scratched

  exposing the iron, rusting will still not occur as zinc is more reactive than iron and will corrode first.