C15.1 - C15.5 - Using Our Recources (Set B)✔️ Flashcards
What causes corrosion? What effect can it have on the metal?
Caused by chemical reactions between metal and substances in the enviorment - the products of corrosion can affect the strength of a metal an its apperance and can lead to it being destroyed
What is rusting?
The corrosion of iron which results in rust forming on the surface of the iron (and most steels) - which can brush of - exposing fresh iron which then rusts and continues until the iron is completley destroyed
How is aluminium protected from corrosion?
Has a protectie oxide layer which protects the aluminium beneath it from further corrosion
4 ways rusting can be prevented on iron and steel?
- coating iron or steel in paint
- coating in oil and greese
- coating in plastic
- coating it with a less reactive metal or more reactive metal
Issues with covering iron and steel in a protective layer?
Once the barrier is even slightly scratched or damaged it will start rusting which spreads under the coating
Explain fully how iron being galvanised protects it from rusting?
Zinc is more reactive than the iron and a stronger reducing agent so it has a higher tendency to form positive ions by giving away electrons - zinc atoms loose electrons and become oxidised therefore any water or oxygen reacts with zinc rather than the iron - refered to a sacrifical protection
Two methods for preventing rusting of iron and steel?
- using a metal coating - so the metal is galvanised
- using a protective barrier eg paint/plastic
Explain sacrifical protection?
The process of using another metal to protect iron or steel from rusting - magnesium, aluminium or zinc are often used - this method is mainly used under harsh conditions like when iron is in contact with seawater (which would accelerate rusting) or when it is likley to be scratched
Equation for rusting?
Iron + oxygen + water → hydrated iron (III) oxide
What is the chemical name for rust?
Hydrated iron (III) oxide - has water loosley bonded in its structure
Why are alloys harder then pure metal? Refer to their structure?
The layers are harder to slide because they are jammed in position as the metal ions are different sizes
What is bronze?
An alloy of copper and tin - tough and resistant to corrosion
What is brass?
Alloy of copper and zinc - a lot harder than copper but can be hammered into sheets
What does the alloy gold normaly consist of?
Silver, copper an zinc - the proportion of gold in the alloy is measured in carats with 24 carat being 100% (pure gold) and 18 carrat being (75% gold) - often used to make jewellery
What are steels?
Alloys of iron that contain specific amounts of carbon and other metals - some steel contain chromium and nickel and are hard and resistant to corrosion
Difference in carbon levels in steel?Explain features?
high carbon steel is strong but brittle and low carbon steel is softer and more easily shaped
Example of the uses of copper alloys?
- statues and decorative items
- ship propellers
Example of the uses of brass alloys?
- used to make musical instruments
- door fittings and taps
Example of the uses of aluminium alloys?
- used to build aircraft
- armour plating on tanks and military vehicles
Example of the uses of gold alloys?
- jewellery
Example of the uses of carbon steel?
- making cars
- making ships
- building structures
Example of the uses of nickel-steel
- make long-span bridges
- military plating on vehicles
What are stainless steels?
Steels that contain a higher percentage of other metals and are even more expensive
Uses of stainless steels? Why are they used for this?
Used in the chemical industry to make reaction vessels and pipework which is often expensive to set up but can withstands high temperatures and pressure as well as corrosive chemicals
Three examples of steels?
- high carbon steel - hard but brittle
- low carbon steels - softer and easily shaped
- stainless steel - resistant to corrosion
What are two thing the properties of a polymer depend on?
-the monomers used to make it
-the conditions chosen to carry out the reaction
What are thermosofening polymers? Explain their features?
Made up of individual polymer chains that are tangled together and are relativley easy to seperate - will soften quite easily when heated an then will re-set and cool down
What are thermosetting polymers? Explain their features?
Polymers which do not melt when we heat then - they have strong convalent bond froming cross -links between their polymer chains
Explain fully what happens when a thermosoftening polymer is heated? Refer to structure?
The forces between the polymer chains are weak - when heated the weak intermolecular forces are broken - the polymer becomes soft once it cools down the intermolecular forces bring the polymer molecules back together and the polymer hardens - this type of polymer can be remoulded
Explain fully what happens when a thermosetting polymer is heated? Refer to structure?
Their monomers make convalent bonds between the polymer chains when they are first heated in order to shape them - these convalent bonds are strong and stop the polymer from softening - the convalent cross-links between chains do not allow them to seperate even if heated strongly - the polymer will char at high enough temperatures
What happens to a thermosetting polymer if heated enough?
Will not soften but will char at high enough temperatures
What is soda glass? What does it consit of?
Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone
What is borosilicate glass? What does it consit of?
made from sand and boron trioxide, melts at higher temperatures than soda-lime glass.
What are clay ceramics?
Include pottery and bricks and are made by shaping wet clay and then heating in a furnace
What are composites?
Usually made of two materials, with one material acting as a binder for the other material - improving a desirable property that could not be offered by the origional material alone
Example of two composites?
- plywood - which is made of thin sheets of wood glued together, with the grain in successive layers
- concrete - made from cement, sand and gravel mixed with water - reinforced with metal rods
How is low density (LD) poly(ethene) formed?
Using high pressure and a trace of oxygen - the polymer chains are randomly branched and cannot pack closely hence the LD
How is high density (HD) poly(ethene) formed?
Using a catalyst at 50 degrees and a slighly raised pressure - HD poly ethene is made up of straighter poly(ethene) chains which can pack more closley together hence the HD
