Topic C6- Global Challenges Flashcards
What is a metal ore?
A metal ore is a rock that contains enough metal to make it economically worthwhile extracting the metal from it.
In many cases, the ore is an oxide of the metal.
How can metals be extracted?
- A metal can be extracted from its ore chemically (through reduction)
- or by electrolysis- which can be used to purify the extracted metal too.
- displacement reactions
- biological methods.
How can a metal be extracted using reduction?
- A metal can be extracted from its ore chemically by reduction using carbon
- When an ore is reduced, oxygen is removed.
- The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon
- Metals higher than carbon in the reactivity series have to be extracted using electrolysis.
- Metal below carbon in reactivity series can be extracted by reduction using carbon
- This is because carbon can only take the oxygen away from the metals which are less reactive than carbon.
How can metals be extracted using electrolysis?
- Metals more reactive than carbon are extracted using electrolysis of molten compounds.
- Once metal is melted, an electric current is passed through it.
- The metal is discharged at the cathode and the non-metal at the anode.
- Electricity is expensive so this process is much more expensive than reduction with carbon.
How can electrolysis be used to purify copper?
- Copper is easily extracted by reduction with carbon.
- The ore is heated in a furnace- this is called smelting.
- But the copper produced this way is impure
- impure copper doesn’t conduct electricity well
- This isn’t useful because a lot of copper is used to male electrical wiring.
- Electrolysis is used to purify copper, even though it is quite expensive.
- This produces very pure copper, which is a much better conductor.
How can you extract metal biologically?
- The supply of some metal rich ores is limited.
- The demand for lots of metals is growing and this may lead to shortages in the future.
- Scientists are looking into new ways of extracting metals from low-grade ores.
- or from the waste that is currently produced when metals are extracted.
- examples include: bioleaching and pytoextraction (they use living organisms!)
What is bioleaaching?
- Uses bacteria to separate metals from their ores
- The bacteria get energy from the bonds between the atoms in the ore
- separating out the metal from the ore in the process.
- The leachate (solution produced by the process) contains metal ions
- which can be extracted by electrolysis or displacement with a more reactive metal.
What is phytoextraction?
- Involves growing plants in soil that contain metal compounds.
- The plants can’t use or get rid of the metals
- so they gradually build up in the leaves.
- The plants can be harvested, dried and burned in a furnace.
- The ash contains metal compounds
- from which the metal can be extracted by electrolysis or displacement reactions.
Give an advantage and disadvantage of biological methods to extract metal from their ores?
- These methods of extraction have a much smaller impact on the environment
- It is a very slow process!!
What is an alloy?
- Alloys can be mixtures of two or more different metals.
- They can also be a mixture of a metal and a non-metal
- Alloys have properties that are different from the metals they’re made from
- these new properties often make the alloy more useful than the pure metal.
What is steel an alloy of?
How is steel better than the original metals?
What are some of its uses?
- Steel is an alloy of iron and carbon
- Steel is harder than iron
- Steel is stronger than iron, as long the amount of carbon does not get greater than approx. 1%.
- Iron on its own will rust quickly, but steel is less likely to rust.
- examples: girders, bridges, engine parts, cutlery, washing machines, saucepans, ships, drill bits, cars etc
What is corrosion?
- Process where something is slowly damaged or destroyed by a chemical process.
- Rusting is a type of corrosion.
What kind of reaction is the rusting of iron?
- It is a redox reaction!
- If iron comes in contact with air and water it will rust.
- rust only happens when iron is in contact with both oxygen and water.
- rust is a form of hydrated iron (III) oxide.
- rusting or iron is a redox reaction. Iron loses electrons when it reacts with oxygen.
- Each Fe atom loses three electrons to become Fe3+, so iron is oxidised.
- Simultaneously, oxygen gains electrons when it reacts with iron.
- Each O atom gains two electrons to become O2-.
- Oxygen is reduced.
What is the equation for rust?
iron + oxygen –> hydrated iron (III) oxide
How can you prevent corrosion?
-By coating the metal with a barrier- this keeps out water oxygen or both:
- painting )ideal for large and small structures
- oiling or greasing (used when moving parts are involved)
- tin plating (where tin is applied to the object- acts as a barrier. Only works as long as tin coating remains intact- if tin is scratched to reveal metal below, it will corrode.
- sacrificial method- place a more reactive metal with whatever metal you don’t want to corrode, e.g. galvanising.
What is the Haber Process used for?
- It is an important industrial process.
- It produces ammonia (NH3), which is used to make fertilisers.
What is the equation for the Haber Process?
N2(g) + 3H2(g) 2NH3(g) (+heat)
**nitrogen and hydrogen reacts to from ammonia- the reaction is reversible, so ammonia breaks down again into nitrogen and hydrogen. The reaction reaches an equilibrium.
Where is hydrogen obtained from in the Haber Process?
The hydrogen can be obtained from hydrocarbons from sources such as natural gas or crude oil.
What are the reaction conditions in the Haber Process?
1) In industry, ammonia is made at a pressure of 200 atm (standard atmosphere) and a temperature of 450ºC in the presence of an iron catalyst.
2) Higher pressures favour the forward reaction (four moles of gas on L-H side, for every 2 moles on the R-H side)
3) So pressure is set as high as possible to give the best yield, without making the plant too expensive to build.
In the Haber Process, what kind of reaction is the forward reaction?
- It is an exothermic reactions,
- which means that increasing the temperature will move the equilibrium position the wrong way
- away from ammonia and towards nitrogen and hydrogen.
- so the yield of ammonia would be greater at lower temperatures.
- but at lower temperatures, there would be a lower rate of reaction.
- so in industry, the temperature is increased anyway to get a much faster rate of reaction.
- the 450ºC is a compromise between maximum yield and speed of reaction.
What happens to the unused hydrogen and nitrogen?
It is recycled so nothing is wasted.
What does the iron catalyst do in the Haber Process (ammonia reaction)?
- The iron catalyst makes the reaction go faster, which gets it to the equilibrium proportions more quickly.
- The iron catalyst doesn’t affect the position of the equilibrium (% yield)
- Without the catalyst, the temperature would be raised even further to get a quick enough reaction,
- that would reduce the & yield even further.
What do fertilisers do?
-They help plants to grow:
- three main essential elements in fertilisers: nitrogen, phosphorus and potassium.
- Plants absorb these nutrients from the soil.
- if plants don’t get enough of these elements, their growth and life processes are affected.
- fertilises replace the missing elements in the soil, or provide more of them.
- this helps increase the crop yield, as the crops grow faster and bigger.
What happens in the Contact Process?
1) Make sulfur dioxide (SO2)- burning sulfur in the air.
2) The sulfur dioxide is then oxidised (with the help of the catalyst vanadium pentoxide) to make sulfur trioxide (SO3)
3) Next, sulfur trioxide is used to make sulfuric acid (H2S04)
What are the temperature conditions for the Contact Process?
1) Oxidising sulfur dioxide to form sulfur trioxide is exothermic.
2) So to get a higher yield of product, you’d think the temperature should be reduced (so equilibrium will shift to the right to replace heat)
3) But reducing the temperature slows the reaction rate down
4) So a compromise temperature of 450ºC is used- to get an acceptable yield quickly.
What are the pressure conditions for the Contact Process?
1) There are two moles of gas on the products side, compared with three moles of gas on the reactants side.
2) So to get a higher yield pf product, you’d think the pressure should be increased (so equilibrium will shift to the right to reduce the pressure
3) But increasing the pressure is expensive (but equilibrium already lies on the right- not necessary)
4) The reaction is carried out at atmospheric pressure.
What are the catalyst conditions for the Contact Process/
1) To increase the rate of reaction, a vanadium pentoxide catalyst (V2O5) is used.
2) It doesn’t change the position of the equilibrium.
What is a life-cycle assessment (LCA)?
-A LCA looks at each stage of the life of a product
- from making the material from natural raw materials,
-making the product from the material,
-using the product and
-disposing the product.
It work out potential environmental impact of each stage.
Why should we conserve fossil fuels?
- They are finite resources (will run out eventually)
- burning them contributes to acid rain and climate change, so it is negatively impacting the environment.
What are the benefits of recycling?
- Only uses small fraction of the energy needed to extract and refine the material from scratch.
- energy isn’t cheap, so recycling saves money!
- finite amount of raw materials- recycling conserves these resources.
- recycling metal cuts down rubbish getting sent to landfills. (Landfills pollute the surroundings and take up a lot of space.)
What are some disadvantages of recycling?
- not an energy-free process. You need energy to reprocess the materials into new forms.
- Items will need sorting out (alloys can be difficult to sort for recycling)
- generally people go for the option that requires them the lowest energy cost (consequences of putting items in a landfill, whether or not the material you are recycling comes from a non-renewable or renewable source.
- you can only recycle materials a finite number of times.
- recycled material is often lower-quality than the original one.
What are the different uses of polymers?
- strong, rigid polymers (e.g. high-density polyethene) are used to make water pipes.
- light, stretchy polymers (e.g. low-density polyethene) are used for plastic bags and bottles.
- polystyrene foam is used in packaging to protect breakable things, and as a thermal insulator.
- heat-resistant polymers such as melamine resin and and polypropene are used to make plastic kettles.
What is fiberglass?
- consists of fibres of glass embedded in a matrix made of a polymer. (matrix = continuous phase in the composites used to hold the reinforcing agent in its place)
- has a low density but is very strong (like glass).
- fiberglass is used to make skis and boats.
What is concrete?
- made from aggregate (sand+gravel) embedded in cement.
- Has a high compressive strength (doesn’t break if squashed).
- this makes it ideal for use as a building material (skate parks)
What is carbon fibre?
- carbon fibre composites have been made using carbon atoms bonded together to make carbon fibres or carbon nanotubes.
- These are held together in a polymer resin matrix.
- These polymers are expensive to make but are very strong and light making them ideal for used in aerospace and sports car manufacturing.
Assess the suitability of polymers for different purposes:
Polymers are:
- really adaptable
- flexible, so are bent without breaking
- easily moulded into almost any shape
- cheaper than most other materials
- they are less dense than most metals and ceramics
- often used for designing products that need low mass
- thermal and electrical insulators
BUT! Polymers can degrade and break down overtime, so polymer products don’t always last long as much as ceramics and metals.
Assess the suitability of ceramics for different purposes:
Ceramics are:
- insulators of heat and electricity.
- brittle and stiff
- strong and hard wearing
- don’t degrade or corrode, so they last longer
Assess the suitability of metals for different purposes:
Metals are:
- good conductors of heat and electricity
- malleable, can be formed into a variety of shapes
- some metals corrode easily, but products made of corrosion resistant metals can last for a very long time.
- less brittle than ceramics or polymers
- likely to deform but stay in one piece, while other materials may shatter.
Assess the suitability of composites for different purposes:
Composites have:
- different properties depending on the matrix or binder and the reinforcement.
- combination of component materials that can be used to be altered
- can be designed to have specific properties for a specific purpose.
BUT! Main disadvantage of composites is that they tend to be much more expensive to produce than other materials.
