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BTEC 2012 UNIT 2 (CHEMISTRY) ASSIGNMENT 3 PHYSICAL & CHEMICAL PROPERTIES
Transcript of BTEC 2012 UNIT 2 (CHEMISTRY) ASSIGNMENT 3 PHYSICAL & CHEMICAL PROPERTIES
Metals form by far the greater proportion of the elements.
They are generally on the left-hand side of the periodic table.
They have properties which differ considerably from those of non-metals and this makes metals very useful for certain purposes. Most materials used to make things are not elements they are mixtures or compounds
these substances are used because they have different chemical & physical properties from elements
some examples are:
sodium azide = compound
motor oil = mixture
steel = Mixture ( a mixture of metals is a called an alloy) Non metals Compounds & mixture
they are solids at room temperature (with the exception of mercury)
they have high melting points and boiling points (with some exceptions)
they are shiny when surfaces are fresh
they are good conductors of heat and electricity
they are malleable (they can be beaten into sheets and shaped)
they are ductile (they can be drawn into wire)
Low melting and boiling points
Cannot conduct electricity (except graphite a form of carbon and silicon which is classed as a SEMI METAL)
Poor conductors of heat Metals The fuels burned in car engines produce LOTS of heat energy.
For car engine to work effectively the engine has to be cooled down
Water & coolant is used to carry heat from the engine to the radiator
The radiator transfers heat from the coolant to the air
Radiators in many cars are made from aluminium Car Radiators http://auto.howstuffworks.com/cooling-system.htm Motor Oil Motor oil is a mixture of hydrocarbons
it has two main functions in the engine:
1. lubricate the moving parts in the engine
2. absorb heat in the engine to cool it.
it also cleans the engine of dirt
to be good at these jobs it needs to have the follwing properties:
it needs to be a good lubricant
it needs to flow through the engine ( to have the correct viscosity)
it needs be a liquid at a wide range of temperatures ( this will allow it to still be liquid in very cold areas & also be able to absorb heat when temperatures are hot
chemical companies have spent million of pounds and a long time developing 'synthetic' motor oils which improve engine performance
If the oil wasn't a good lubricant friction would increase wearing down the engine parts leading to breakdowns. If the oil had the wrong viscosity it may be too thick to flow or too thin to lubricate
If the oil could not absorb heat the engine may overheat http://auto.howstuffworks.com/synthetic-motor-oil1.htm Fire Extinguishers Oxygen, heat & fuel are needed for fires to burn, fire extinguishers work by removing either heat or oxygen
Water cant be used with petrol or electrical fires
Carbon dioxide or foams need to be used to remove the oxygen
carbon dioxide is useful because it doesn't react with the fuel or cause problems with electrical circuits
In a carbon dioxide extinguisher, the carbon dioxide is kept in pressurized liquid form in the cylinder. When the container is opened, the carbon dioxide expands to form a gas in the atmosphere.
Carbon dioxide gas is heavier than oxygen, so it displaces the oxygen surrounding the burning fuel. Air Bags- Sodium Azide http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/airbag1.htm http://home.howstuffworks.com/home-improvement/household-safety/fire/fire-extinguisher2.htm sodium azide is a stable chemical which breaks down rapidly (when heated to 300C) to produce lots of nitrogen gas
2 NaN3 --> 2 Na + 3 N2
A handful (130 grams) of sodium azide will produce 67 liters of nitrogen gas--which is enough to inflate a normal air bag.
sodium azide is TOXIC so car manufacturers must ensure it all reacts computer chips - silicon Silicon is the second most abundant element in the earth's crust
Sand has a high percentage of silicon. Silicon - the starting material for computer chips - is a semiconductor ( it doesnt conduct as well as a metal) It can be readily turned into an excellent conductor or an insulator of electricity, by adding small amounts of other elements.
Single crystals of very pure silcon are used to make computer chips
they are sliced very thinly and layered to form the parts of computer chips www.howstuffworks.com/diode.htm