Obtaining and Using Metals (1) Flashcards
Define
oxidation.
(in terms of oxygen)
the gain of oxygen by an element or compound
Define
reduction.
(in terms of oxygen)
the loss of oxygen from a compound
What reactions does
combustion involve?
oxidation and reduction
this process is always exothermic
What are three characteristics of
metals at the top of the reactivity series?
- they are the most reactive
- they easily lose their electrons to form cations
- they are oxidised more easily
What are two ways to
find an order of reactivity from experiments?
- compare the relative reactivity of different metals with either an acid or water
- measure the temperature change of a reaction with an acid or water over a set time period
What is the general equation for the reaction of
metals with water?
metal + water -> metal hydroxide + hydrogen
What happens when you react a
metal with a salt solution?
If you put a reactive metal into a solution of a less reactive metal salt, the reactive metal will replace the less reactive metal in the salt.
If you put a less reactive metal into a solution of a more reactive metal salt, nothing will happen.
Define
oxidation.
(in terms of electrons)
oxidation is a loss of electrons
OILRIG
Define
reduction.
(in terms of electrons)
reduction is a gain of electrons
OILRIG
What are
displacement reactions?
a type of redox reaction in which a more reactive element reacts to take the place of a less reactive element in a compound
Define
metal ore.
a rock which contains enough metal to make it profitable to extract the metal from it
How can metals be
extracted from their ores?
A metal below carbon in the reactivity series is extracted from its ore by reducing it in a reaction with carbon. In this reaction, the ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised.
Metals higher than carbon in the reactivity series have to be extracted using electrolysis, which is expensive.
Describe how you would extract
aluminium from bauxite using electrolysis.
(5 steps)
- The main ore of aluminium, bauxite, would be mined and purified to give aluminium oxide.
- As aluminium oxide has a very high melting point (over 2000°C) and melting it would be very expensive, it is dissolved in molten cryolite (a less common ore of aluminium). This brings the melting point down to about 900°C which saves energy, making the process cheaper and easier.
- The electrodes are made of graphite. The aluminium cations are attracted to the negative graphite lining (which acts as the cathode) where they pick up electrons and turn into neutral aluminium atoms. These sink to the bottom of the electrolysis tank.
- The oxygen anions are attracted to the anode where they each lose two electrons. The neutral oxygen atoms combine to form O2 molecules.
- Some of the oxygen produced reacts with the carbon in the electrode to produce carbon dioxide.
This is why the anodes have to be replaced every now and again.
What are the disadvantages of
extracting metals by electrolysis?
(3)
- large amounts of electricity are necessary
- electricity is expensive so electrolysis is expensive
- melting and/or dissolving the metal ore is also costly
What are the advantages of
extracting metals using reduction?
(with carbon) (2)
- much cheaper than electrolysis
- carbon is cheap
What are two examples of
new methods to extract metals from low-grade ores?
- bioleaching
- phytoextraction
What is
bioleaching?
a bacterial method of extracting metals which uses bacteria to convert metal compounds in the ore into soluble metal compounds, separating out the metal from the ore in the process
the leachate (the solution produces by the process) contains metal ions which can be extracted (for example by displacment or electrolysis)
What is
phytoextraction?
(intro + 3 steps)
A process that involves growing plants in soil that contains metal compounds.
- The plants can’t use or get rid of the metals so the metal compounds gradually build up in the leaves.
- These plants can be harvested, dried and burned in a furnace.
- The ash contains metal compounds from which the metal can be extracted by displacement or electrolysis.
What are the advantages of
new methods of metal extraction?
(4 advantages)
(1 disadvantage)
- less damaging to the environment (compared to traditional methods)
- inexpensive
- require less energy (which is also good for the environment)
- protects habitats as low-grade ores don’t need to be mined in the same way as high-grade ores
The disadvantage of these new extraction methods is that they’re slow.
What is
recycling?
using waste materials to make new products
What are the four key
advantages of recycling?
- it conserves energy
- it conserves resources
- there are environmental benefits
- there are economic benefits
How does recycling
conserve energy?
and why is this a good thing?
Recycling materials saves lots of energy as the process uses only a fraction of the energy needed to extract and refine raw materials.
This is a good thing because lots of the necessary energy comes from burning fossil fuels but:
- fossil fuels are running out so it’s important to conserve them
- burning fossil fuels contributes to acid rain and climate change
Why is
conserving resources by recycling
a good thing?
There’s a finite amount of many raw materials so it’s important to conserve them.
It’s particularly important to recycle materials that are rare.
What are some of the
environmental benefits of recycling?
(2 key points)
- Recycling more metals means that we don’t need so many mines. - Mines are damaging to the environment and destroy habitats, aswell as being a bit of an eyesore.
- Recycling materials also cuts down on the amount of rubbish that gets sent to landfill. - Landfill takes up space and pollutes the surroundings.
