C6 Flashcards
What is a metal ore?
A rock which contains enough metal to make it economically worthwhile to extract the metal from it.
What is metal ore often in the form of?
It is often a metal oxide.
What are the two ways of extracting metal from ore chemically?
By reduction with carbon or by electrolysis.
What other ways are there of extracting metal from ore?
Displacement reactions and biological methods.
What is metal extraction by reduction?
It can be extracted through reduction with carbon, meaning that its oxygen is removed from the ore.
When can metal be extracted by reduction?
If it is below carbon on the reactivity series.
What are the metals that are higher than carbon on the reactivity series extracted by?
Electrolysis, which is expensive.
Where is the metal deposited during electrolysis?
At the cathode
Why is copper purified when extracted by carbon?
The copper produced by reduction with carbon is impure, which doesn’t conduct well which is important as copper is used to make electrical wiring. So it is purified through electrolysis.
How is carbon purified through electrolysis?
The anode is made of non-inert copper so that it dissolves in the electrolyte and forms at the cathode.
Why are scientists looking for ways of extracting metal from low grade ores?
Because the supply of metal rich ores is limited but the demand for metal is growing which may lead to shortages.
What are the biological methods used for extracting metals?
Bioleaching and Phytoextraction
What is Bioleaching?
This 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.
What is produced by Bioleaching?
Leachate, which contains metal ions and can be extracted by displacement or electrolysis.
What is Phytoextraction?
This involves growing plants in soil that contains metal compounds. The plants can’t use/get rid of the metals and so they build up in the leaves. The plants can be harvested, dried and burned in a furnace.
What are the advantages/disadvantages of Bioleaching and Phytoextraction?
They are safer for the environment than non-biological methods but they are very slow.
What is an alloy?
A mixture of two or more different metals, or a mixture of a metal and non-metal.
Why are alloys used?
They have properties that are different from the metals that they are made from which are more useful.
What is steel an alloy of?
Iron and carbon
What are the properties of steel?
It’s harder and stronger than iron. Iron is much more likely to rust (corrode) than steel. Its used to make things like bridges, engine parts, washing machines etc.
What is brass an alloy of?
Copper and zinc
What are the properties of brass?
A mixture of properties from copper and zinc, although brass is harder than either of them. Its used to make things like musical instruments and screws.
What is bronze an alloy of?
Copper and tin
What are the properties of bronze?
It’s much harder and stronger than copper or tin, and it’s more resistant to corrosion. Its used to make things like springs and motor bearings.
What is solder an alloy of?
Lead and tin
What are the properties of solder?
It doesn’t have a definite melting point but gradually solidifies as it cools, making it useful for joining metal things together.
What is duralumin an alloy of?
Aluminium, with small amounts of copper, magnesium and manganese
What are the properties of duralumin?
It’s a very low density alloy that is much stronger than aluminium. As a result its useful for making things like parts of aeroplanes.
What is corrosion?
A process where something is slowly damaged or destroyed by a chemical process.
When does iron rust?
It rusts when it comes into contact with air and water. Rust is a form of hydrated iron(III) oxide.
What is the equation that shows the formation of rust?
Iron + Oxygen + Water → Hydrated iron (III) oxide
Why is the rusting of iron a redox reaction?
Iron lose electrons when it reacts with oxygen. Each Fe atom loses 3 electron atoms to become Fe³⁺. Simultaneously, oxygen gains electrons - each O atom gains two electrons to become O²⁻.
How can you prevent corrosion?
You can prevent corrosion by coating the metal with a barrier. This keeps out the water, oxygen or both.
What methods are there to prevent corrosion?
Paint, oil, grease.
How does a coat of tin prevent steel from corroding?
The tin acts as a barrier, stopping water and oxygen reaching the surface of the metal. This only works when the coat of tin remains intact.
What is the “sacrificial” method of preventing corrosion?
You place a more reactive metal with whatever you don’t want to corrode, and the water and oxygen react with this instead of the desired metal.
What is galvanising?
Where a coat of zinc is put onto an iron object to prevent rusting. It’s more reactive than iron so it’s lose electrons (and corrode) in preference to iron.
What does the Haber process do?
It produces ammonia (NH₃) which is used to make fertilisers.
What is the equation of the Haber process?
N₂ + 3H₂ ⇌ 2NH₃ (+ heat)
How is nitrogen and hydrogen obtained for the Haber process?
Nitrogen is easily obtained from the air which is 78% nitrogen. Hydrogen can be obtained from hydrocarbons from sources such as natural gas or crude oil.
At what pressure and temperature is ammonia produced at?
200 atm and 450 degrees celsius
Why do higher pressures favour the forward reaction (production of ammonia) in the Haber process?
There are four moles of gas on the left hand side and so the equilibrium will move to the left hand side, therefore producing more ammonia.
Why do lower temperatures favour the production of ammonia in the Haber process?
The forward reaction is exothermic, and so higher temperatures would mean that less ammonia is produced. Therefore reducing the temperature increases the yield of ammonia.
Why is the Haber process performed at only 200 atm and 450 degrees celsius when lower temperatures/higher pressures would have a higher yield?
Lower temperatures mean a lower rate of reaction - 450 degrees celsius is a compromise between maximum yield and rate of reaction.
What type of catalyst is used in the Haber process and why?
Iron - it makes the reaction quicker and makes it reach the equilibrium proportions quicker. It’s important as, without it, temperatures would have to be higher which would decrease yield even more.
What are fertilisers made up of?
The three main essential elements in fertilisers are nitrogen, phosphorus and potassium.
Why are fertilisers used?
They replace the missing elements if they aren’t present in the soil, or provide more fo them. This increases yield and the crops grow bigger/faster.
How is ammonia changed into fertilisers?
It’s a base and can be neutralised by acids to make fertilisers (ammonium salts)
What different ammonia-based fertilisers are there?
Ammonium phosphate
Why is ammonium nitrate such a good fertiliser?
It’s an especially good fertiliser because it has a high percentage of nitrogen, the ammonia and the nitric acid.
How do you make ammonium nitrate?
It’s produced by neutralising nitric acid with ammonia.
How do you make ammonium sulfate?
By neutralising sulfuric acid with ammonia.
How do you make ammonium phosphate?
By neutralising phosphoric acid with ammonia.
How can you make most fertilisers?
Titration
What is the Contact Process used for?
To make sulfuric acid
What is the first stage of the Contact Process?
S + O₂ → SO₂
What is the second stage of the Contact Process?
2SO₂ + O₂ ⇌ 2SO₃
What is the third stage of the Contact Process?
SO₃ + H₂O → H₂SO₄
Is the oxidation of sulfur dioxide exothermic or endothermic?
Exothermic
How is temperature set in the Contact Process?
Although having a low temperature would increase the yield because it’s an exothermic reaction, this would slow down the rate of reaction and so they compromise at 450 degrees celsius.
How is pressure set in the Contact Process?
There is 2 moles of gas of products and 3 moles of gas of reactants. To increase yield, you’d increase the pressure but that would be very expensive. As a result, it’s usually carried at atmospheric pressure.
What catalyst is used in the Contact Process?
Vanadium pentoxide. This doesn’t affect the equilibrium position.
What are the 5 things that need to be considered in industrial processes?
Cost of raw materials Availability of raw materials Energy costs Rate Equilibrium position
How does the cost of raw materials affect industrial processes?
Raw materials often have to be refined or purified, or produced with another reaction. This affects whether the process is economically viable and may make it unprofitable.
How does the availability of raw materials affect industrial processes?
Some raw materials, like crude oil, are non-renewable, so they aren’t sustainable. It’s best to get materials that are renewable or common.
How does the energy cost affect industrial processes?
Generally, higher temperatures and pressures cost more to maintain, so low temperatures/pressures are used wherever possible.
How does the rate of reaction industrial processes?
Sometimes yield is compromised to have a reasonable rate.
How does equilibrium position affect industrial processes?
Being able to control the position of equilibrium to maximise yield is important in making processes profitable.
What is a life-cycle assessment?
It looks at each stage of the life of a product and works out the potential environmental impact of each stage.
Describe the “Choice of material” life-cycle assessment
Metals have to be mined and extracted, which requires lots of energy and cause pollution. Raw materials for chemical manufacture come from crude oil which is unsustainable.
Describe the “Manufacture” life-cycle assessment
Manufacturing requires lots of energy and resources. It also causes lots of pollution. You need to think about waste products and how to dispose them - some can be recycled into other useful chemicals.
Describe the “Product use” life-cycle assessment
Fertilisers can leach into streams/rivers and damage ecosystems
Describe the “Disposal” life-cycle assessment
Products might be incinerated which causes air pollution.
Where does lots of the energy come from when extracting raw materials?
Burning fossil fuels.
What is the issue with using fossil fuels?
They’re running out and are unsustainable. They also contribute to acid rain and climate change.
Why is recycling so good?
Recycling often uses a small fraction of energy needed to extract and refine the material from scratch.
There’s a finite amount of resources on earth, so recycling conserves them.
Recycling cuts down on landfill.
How much is saved for every 1 kilogram of aluminium cans recycled?
Roughly 95% of the energy needed to mine and extract aluminium
4 kg of aluminium ore
Lots of waste
What are issues with recycling?
Not completely energy free - might not even be worth it.
Items need sorting to separate materials.
You can only recycle something a finite number of times.
What are ceramics?
Ceramics are made by baking substances, such as clay, to produce a brittle, stiff material. Examples include glass, porcelain and bone china.
