Flashcards in Extraction And Uses Of Metals Deck (49)
How are most metals found?
Most metals do react with other elements to form compounds. Which can be found naturally in the Earth's crust. If a compound is worth extracting. The compound is called a metal ore (these are finite resources).
What is the most common compound for an ore?
The metal with the oxygen, so the metal oxide
How do you extract metals LESS REACTIVE than carbon?
A reduction reaction takes place.
The most common reducing agent is carbon.
The metal oxide (ore) is heated with carbon monoxide.
Carbon is more reactive than eg iron so 'steals' the oxygen.
How do you extract metals MORE REACTIVE than carbon?
Very reactive metals form stable ores, so it is difficult to separate the metal from the oxide.
So metals that are more reactive than carbon have to be extracted using electrolysis. The metal ions are given electrons by the cathode. This process is expensive.
What is the main ore of aluminium?
Bauxite, and after mining and purifying, pure aluminium oxide is left.
What is aluminium oxide dissolved in?
Molten cryolite (a less common ore of aluminium)
Why is aluminium oxide dissolved in molten cryolite?
Aluminium oxide has a very high melting point (over 2000 degrees) so it would be very expensive to melt.
Dissolving it in molten cryolite, reduces the melting point (of the mixture) to about 900 degrees, which makes the process much cheaper and easier.
It lowers the operating temperature
What are the electrodes made of?
Carbon, they have to be replaced regularly as due to high temperatures they burn in the oxygen to form carbon dioxide.
Describe what happens during the electrolysis of aluminium oxide
Molten aluminium oxide contains free ions, so will conduct electricity
The Al3+ ions go to the cathode, and molten Al forms at the bottom
The O2- ions go to the anode, where they lose electrons
The O2 reacts slowly with the carbon anodes, forming CO2. Therefore, because the anode is constantly getting worn down, it often needs replacing.
What kind of reaction is the electrolysis of aluminium oxide and what is the equation?
2Al2O3 = 4Al + 3O2
What equation happens at the cathode during the electrolysis of aluminium oxide?
Al3+ + 3e- = Al (reduction because the ions gain electrons)
What equation happens at the anode during the electrolysis of aluminium oxide?
2O2- = O2 + 4e- (oxidation)
Why is the electrolysis of aluminium oxide expensive?
It uses a lot of electricity
Energy is needed for heat
The replacement of the anodes
Where can iron ore be found?
Australia, Canada and Millom
What is the name for iron ore?
How is iron extracted from the iron ore?
By reduction in a blast furnace. The raw materials and process is relatively cheap.
What are the raw materials used in the extraction of iron?
Iron ore - containing iron
Coke - almost pure carbon, for reducing the Fe2O3
Limestone - takes away the impurities in the form of slag
Describe the process of reducing the iron ore to iron in the blast furnace including equations
1) Hot air is blasted into the furnace, making the Coke burn much faster than normal. This raises the temperature to about 1500 degrees
2) The Coke burns and produces CO2:
C + O2 = CO2
3) The CO2 reacts with the unburnt Coke to form CO:
CO2 + C = 2CO
4) The CO then reduces the iron ore to iron:
3CO + Fe2O3 = 3CO2 + 2Fe
5) The iron is molten at this temperature and also very dense, so it runs straight to the bottom of the furnace where it's tapped off
What is the main impurity in the iron ore?
SiO2. This is still solid and would tend to stay mixed with the iron. The limestone removes it.
Describe the process of removing the impurities in iron including equations
1) The limestone is decomposed by the heat into CaO and CO2:
CaCO3(s) = CaO(s) + CO2(g)
2) The CaO then reacts with SiO2 to form calcium silicate:
CaO(s) + SiO2(s) = CaSiO3(l) (molten slag that can be tapped off) - this is a neutralisation reaction
What are the uses of slag (when cooled)?
Road building, fertiliser
Properties of aluminium
Resistant to corrosion because of passive oxide layer
Relatively strong when alloyed
Uses of aluminium (in relation to properties)
Manufacture of kitchen foil + high voltage electricity cables
Because it doesn't corrode easily, useful for products that come into contact with water e.g. drink cans
Relatively light metal: bicycle frames and aeroplanes
What is the name of iron that comes out of the blast furnace and it's characteristics
Pig iron, 96% pure, therefore brittle and useless
Uses of pure iron (or can be said it's useless because it's too soft)
Wrought iron (almost 100% pure) is malleable and can be used to make ornamental gates and railings. Has now been largely replaced with mild steel as it is much harder and wrought iron is not suitable for constructive purposes.
What happens to pig iron and what does it make
It is purified then mixed with other elements to make alloys
What are the two main alloys of iron?
Properties and uses of cast iron
Combination of iron, silicon and carbon (4%)
Hard but brittle
Used to make manhole covers and gutterings and drainpipes
What do the properties of steel depend on?
The amount of different elements added
The form of heat treatment the steel has undergone
What are the two types of steel?
What are carbon steels?
Most common steel, contain 0.03% - 1.5% carbon
Two types of carbon steel
Low carbon steel
High carbon steel
Properties and uses of low carbon steel
Contains less than 0.1% carbon
Soft and malleable
Used in car body manufacture
Properties and uses of high carbon steel
Contains about 0.25-1.5% carbon
Used for knives and tools, masonry nails
Properties and uses of stainless steel
Does not rust
Contains chromium and nickel
Relatively expensive to manufacture
Used for cutlery, kitchen sinks, saucepans and gardening tools.
What is the main problem with iron?
That it corrodes easily (rust)
How are metals that are unreactive found?
They don't tend to form compounds with other elements so are found in combined underground eg gold
How to remove the metal from the oxide?
You have to remove the oxygen, this is called reduction. You would have to add electrons to the positive ion, this is also called reduction.
what are the two main economic factors to take into account when thinking about methods of extraction?
• the cost of energy
• the cost of the reducing agent
What is a metal ore?
An ore contains enough of the mineral that is wanting to be extracted for it to be worthwhile to extract the metal.
How is titanium extracted from its ore?
It is heated with a more reactive metal. This is very expensive because the more reactive metal will have had to be extracted by an expensive process first.
what does native mean?
A metal that is found not in an ore, this is very rare and an example is gold.
Uses of aluminium:
Pure aliminium isn't very strong so aliminium alloys are normally used.
It is used for the construction of planes and pots and pans. and electricity cables.
What properties of aluminium alloys make it suitable to use in planes?
It resists corrosion, has a low density and is strong.
What properties of aluminium alloys make it suitable to use in pots and pans?
It has a shiny appearance, resists corrosion, has a low density and is a good conductor of heat.
What properties of aluminium alloys make it suitable to use in electricity cables?
It resists corrosion, has a low density and is a good conductor of electricity. The cables are strengthened by a core of steel.
What is mild steel?
iron containing up to about 0.25% of carbon. This increases the hardness and strength.
What is mild steel used for?
Wire, nails, car bodies, ship building and bridges.