C15 Flashcards
What is corrosion caused by?
The chemical reactions between the metals and substances in the environment.
What is rusting?
It is the corrosion of iron.
What is the equation for the rusting of iron?
Iron + oxygen + water = hydrated iron oxide
How can rust be prevented?
Air and water needs to be kept away, so by means of oil, grease, plastic and paint. You can also use a more or less reactive metal.
What does it mean when iron is galvanised?
When you use a more reactive metal to coat iron. Therefore zinc is more likely to give away electrons, to form an ion becoming oxidised. Therefore any water or oxygen reacts with the zinc instead of the iron, which is called sacrificial proteciton.
When is sacrificial protection used?
When a coating is likely to be scratched so it protects even when scratched.
What is steel?
It is an alloy of many different metals and elements.
How are carbon steels made?
Made by removing most of the carbon from the iron obtained from a blast furnace. Cheapest steel to make.
What are stainless steels?
They are chromium-nickel steels which combine hardness and strength with good resistance to corrosion. They do not rust.
What is the difference between high carbon steels and low carbon steels?
High carbon steels are very strong but brittle but low carbon steel is soft and easily shaped. It is less likely to shatter though.
What do the properties of a polymer depend on?
The monomers used to make it and the conditions chosen to carry out the polymerisation reaction in.
How is low density polyethene made?
By using very high pressures and a trace of oxygen, ethene forms it.
What are characteristics of low density polyethene?
The polymer chains are randomly branched and cannot pack closely together, hence the low density.
How is high density polyethene made?
Through using a catalyst at 50 degree Celsius and a slightly raised pressure, ethene makes it.
What are characteristics of low density polyethene?
They are closely packed together, and made of straight polyethene chains. It has a higher softening temperature and is stronger.
What are thermosoftening polymers?
They are made of individual polymer chains that are tangled together. They soften easily when heated and reset when they cool down.
What are thermosetting polymers?
They do not melt when heated. They have strong covalent bonds forming ‘cross links’ between their polymer chains.
What are the forces like between thermosoftening polymers?
They are weak and when heated the weak intermolecular forces break, making it soft. When it cools down they come back together and it hardens again.
What are forces between thermosetting polymers like?
Their monomers make covalent bonds between the polymer chains when first heated in order to shape them. Therefore the covalent bonds inbetween chains do not allow them to separate even if heated. It will char at high temperatures.
What is sand made of?
Sand, limestone and sodium bicarbonate.
How is glass made?
They heat the raw materials to 1500 degrees, where they melt it and react them to from molten glass. As it cools it turns into a solid but the particles do not form a regular pattern but a disorderly structure.
How are ceramics made?
Moulding wet clay into desired shapes then heating them to around 1000 degrees.
How is clay arranged?
It is made of compounds of metals and non-metals with ionic bonding between ions, but also has some covalent bonding between non-metal atoms. They are arranged in giant structures which form layers.
