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13/07/2014 Rusting and Corrosion • L.O. • I have learnt about the conditions for rusting and which metals corrode. 8:37 PM
Chemical Changes In chemical changes a new substance is made and the change is hard to reverse. Examples of chemical changes? Making glass Burning coal Rusting Boiling an egg Baking a cake Is eating food a physical or chemical change? Discuss!
Many metals react with oxygen in the air. Over time, a thin layer of metal oxide covers the surface of the metal. We call this tarnishing. Some metals carry on reacting below the surface and their structure is destroyed. This corrosion wears away the metal. You can prevent this by painting the metal. How does the paint stop the metal tarnishing? Or you can choose a metal that does not react with the air – like gold. But a gold bridge would be very expensive!
Keywords a metal breaking down by reacting with oxygen (and sometimes moisture) a compound containing only a metal and oxygen to gather a thin layer of discoloration by reacting with the air describes a material that does not react a thin layer of green on the surface of copper the corrosion of iron, which reacts with oxygen and water to form flaky iron oxide rusting corrosionunreactive metal oxidetarnishing patina Match each word or phrase with its correct meaning. corrosion metal oxide tarnishing unreactive patina rusting
Gather round to record the results of a ‘Rusting’ experiment set up and to set up a second. 8:37 PM
Iron & Aluminium When iron corrodes, it forms a layer of rust. Rust is porous; it lets air through. Draw lines through the rust in the diagram to show how air can attack the iron underneath.
When aluminium corrodes, it forms a layer of aluminium oxide. Explain why air cannot attack the aluminium metal. It is protected by the layer of aluminium oxide. If the surface of the corroded aluminium gets scratched, the air can get to the aluminium. The air reacts with the exposed aluminium forming aluminium oxide, which then protects the aluminium under the scratch
Interpreting Data may be rusty where paint has chipped but less so than Sam’s or Alex’s bike Corroded to form a layer of aluminium oxide so no longer shiny may be rusty where paint has chipped rusty may be rusty where paint has chipped Corroded to form a layer of aluminium oxide so no longer shiny may be rusty where paint has chipped but less so than Sam’s or Alex’s bike Rusty but less so than Sam’s bike
Iron is a metallic (polymer / element / compound) used to make things such as: (reinforced concrete / cars / polythene bottles / nails / warm clothing / suspension bridges). Steel is an alloy made mainly of (carbon / titanium / iron). Some types of steel rust much more slowly than iron. The rust forms a (blue / red / yellow) coating on the (inside / surface) of the metal.
When iron and steel get wet they will rust, but only if oxygen is (absent / present / oxidised). The oxygen comes from the (Sun / air / core of the Earth). The layer of rust traps water and air Next to the surface. This layer (protects / damages) the iron underneath. If aluminium is used instead of iron, the surface of the aluminium (also corrodes / remains unharmed). The aluminium oxide then (eats into / protects) the metal beneath.