This week we are thinking about 2 important chemical reactions that result in rust forming on certain metals and certain materials burning.

Please watch the video clip below as an introduction to the lesson. 

When objects rust, they are undergoing a chemical change. The iron is combining with oxygen from the air and water. This process is known as oxidation. Steel also rusts because it is an alloy of iron. This means that it is made by combining iron with a different chemical such as carbon.

Here is a short video clip which shows how an object rusts.

www.bbc.co.uk/education/clips/zc89wmn

www.bbc.co.uk/education/clips/z4d9wmn

Many important structures such as bridges contain iron and so it is important to prevent them from rusting as this causes corrosion and can reduce the strength of the structure. We use methods such as painting the surface of iron to prevent the water and oxygen from reaching it. 

Rusting

Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur. This experiment is similar to the one we would do in class. In the experiment below, the nail does not rust when air - containing oxygen - or water is not present:

Calcium chloride absorbs water in the right-hand test tube

Salt dissolved in water does not cause rusting, but it does speed it up, as does acid rain.

Aluminium does not rust - corrode. Its surface is protected by a natural layer of aluminium oxide. This prevents the metal below from coming into contact with air and oxygen.

Unlike rust, which can flake off the surface of iron and steel objects, the layer of aluminium oxide does not flake off.

How can we prevent rusting?

Galvanization

The process of galvanization involves coating the surface with an external layer of metallic zinc. This is accomplished through hot-dip galvanizing or electroplating. The zinc layer prevents corrosive substances from penetrating further into the metal. 

Organic coating

Organic coatings such as paint are a cost effective way to protect against rust. Organic coatings form a barrier against corrosive elements. Oil based coatings are ideal for preventing penetration of water and oxygen. Typical organic coatings are 15 to 25 micrometers thick.

Powder coating

A dry powder is evenly applied to a clean surface. Next, the object is heated, turning the powder into a thin film. There are a wide range of powders available including acrylic, polyester, nylon, vinyl, epoxy and urethane.

Regular maintenance

Regular maintenance is advised to stop rust forming and halt the progress of any rust that occurred. It’s essential to remove any rust that has formed. A razor blade can be used for small areas. Next any surface grime should be removed using warm water and soap. Lastly a rust resistant coating should be applied to the surface.

Now lets think about the second common chemical reaction for today...Burning. Please watch the video below.

For an object to begin to burn it needs fuel, oxygen (usually from the air) and heat. Once the object, which is usually the fuel, is burning it produces its own heat. We can put fires out by removing one of these 3 things. In fire extinguishers water is used to remove the heat, foam or powder can be used which lays on top of the burning material and prevents oxygen getting to the fuel. Once the fuel has all been used up the fire will also go out. 

Task: As today is the last lesson in this topic we are going to do an escape room as the task. First , go through the introduction to the scenario. Then below are the clues which are all to do with our topic. each clue gives you a number which build up into a code to escape the kitchen. Record your answers on the second sheet. We will meet up towards the end of the lesson to go through the answers but before that please send me a photo of your answers in the science channel of Teams. Thank you.