Extraction of Metals Flashcards
How does the reactivity of a metal affect its extraction?
More reactive the metal, more difficult it is to extract from its ore.
What method of extraction can be used for extracting more reactive metals?
Electrolysis
What is an example of a more reactive metal?
Aluminium
What method of extraction can be used for extracting less reactive metals?
Reduction
What is an example of a less reactive metal?
Iron
What is phytomining?
Use of plants to absorb metal compounds from soil as part of metal extraction.
What are the steps involved in phytomining?
- Plants very good at absorbing metal compounds through their roots are grown on ground containing low-grade ores, so metal is removed from ore and enters plant.
- Plants are harvested, dried and burnt to produce ash rich in metal compounds.
- Acid such as sulfuric acid added to ash and insoluble metal compounds react to produce solution containing soluble copper compounds (leachate).
- Metal can be obtained by adding scrap iron to leachate solution, displacement reaction will occur. Iron is more reactive than copper in solution and so copper is displaced by iron.
What is the ionic equation for the displacement reaction of iron and the copper leachate?
Fe(s) + Cu2+(aq) > Fe2+(aq) + Cu(s)
What are the advantages of phytomining?
Better for environment.
Produces energy when plants are burnt.
No noise pollution.
No dust pollution.
No transport of rock.
No traffic.
No light pollution.
What are the disadvantages of phytomining?
Slow process as plants need to grow.
Supply is seasonal rather than continuous.
What are the 3 stages of the blast furnace extraction method?
- Formation of reducing agent
- Reduction of iron oxide (haematite)
- Removal of acidic impurities
What is the process of extracting iron from haematite in a blast furnace?
- Iron ore, coke and limestone placed into blast furnace and hot air blasted through it.
- Causes coke to react to form carbon dioxide and further reaction turns this into carbon monoxide which is reducing agent.
- Iron(III) oxide (iron ore) reacts with carbon monoxide and is reduced to form iron and carbon dioxide.
- Iron is dense and so sinks to bottom of blast furnace where is tapped off.
- Limestone is thermally decomposed to form calcium oxide.
- Calcium oxide is basic and reacts with acidic impurities to form molten slag (calcium silicate).
- Molten slag can be tapped as is less dense than molten iron.
What are the word equations for the formation of the reducing agent?
Coke + Oxygen > Carbon dioxide
Carbon dioxide + Coke > Carbon monoxide
What is the word equation for the reduction of the iron(III) oxide to iron?
Iron(III) oxide + Carbon monoxide > Iron + Carbon dioxide
What are the word equations for the removal of the acidic impurities?
Calcium carbonate > Calcium oxide + Carbon dioxide
Calcium oxide + Silicon dioxide > Calcium silicate
At what temperature is the iron formed in the blast furnace molten?
2,000oC
What is thermal decomposition?
Breakdown of a substance using heat.
What is the main impurity in the iron(III) oxide?
Sand (silicon dioxide)
What is slag used for?
Road building
What are the uses of iron?
Used in bridges and structures due to its strength.
Pig iron produced in blast furnace is soft and mixed with carbon to produce alloy steel, to increase its strength.
What is the overall process for manufacturing iron?
- Iron ore, coke and limestone placed into blast furnace and hot air blasted through it.
- Causes coke to react to form carbon dioxide.
- Further reaction turns carbon dioxide into carbon monoxide which is reducing agent.
- Iron(III) oxide reacts with carbon monoxide and reduced to form iron and carbon dioxide.
- Iron is dense so sinks to bottom where is tapped off.
- Limestone is thermally decomposed to form calcium oxide.
- Calcium oxide is basic and reacts with acid impurities (calcium silicate) to form molten slag.
- Molten slag can be tapped off as less dense than molten iron.
What is electrolysis?
Breakdown of molten or aqueous ionic compound by passing electricity through it.
What is an electrolyte?
Ionic compound that is molten or aqueous that conducts electricity and is decomposed by it.
What is an electrode?
Conducting rods that are placed into molten ionic compound.
How do metals conduct electricity?
Conduct in solid state and not broken down.
Achieved by movement of delocalised electrons.
How do ionic compounds conduct electricity?
Conduct in liquid (molten or aqueous) state so ions are free to move and carry a charge.
Decomposed by electrolysis.
What is the positive electrode called?
Anode
What is the negative electrode called?
Cathode
What are the electrodes made of?
Graphite
Why is graphite used for the electrodes?
Good conductor of electricity.
Inert / unreactive.
Why must the electrodes be replaced after a while?
Carbon in graphite reacts with oxygen produced to from carbon dioxide, wearing away electrodes.
Why must the ionic compound be heated?
Needs to be molten so ions are free to move and carry a charge.
What is the name of aluminium ore?
Bauxite
What is formed when bauxite is purified?
Aluminium oxide (alumina).
Why is cryolite added during the electrolysis of aluminium?
Reduce melting point of alumina to 900oC to save energy and reduce costs.
Increase conductivity.
Why is recycling aluminium better than extracting it from bauxite?
Cheaper as uses only fraction of energy used in extraction.
Saves waste.
Better for environment.
What is the process of electrolysis of sulfuric acid?
- Sulfuric acid solution splits up by electricity to produce H+ ions, OH- ions and SO4 2- ions.
- H+ ions move to cathode and discharge to produce H atoms, combine to form H2.
- OH- and SO4 2- ions move to anode and discharge to produce O atoms, combine to from O2.
- Sulfate ions are unchanged due to preferential discharge of OH-.
