Topic 4 extracting metals and equilibria

• oxidation

  the loss of electrons

  -gain of oxygen
• reduction

  the gain of electrons.

  -loss of oxygen
• OILRIG


  oxidation is loss of electrons

  Reduction is gain of electrons
• redox reactions

  when oxidation and reduction happen simultaneously

  eg. displacement reactions
• what are unreactive metals presented as?

  as uncombined elements in the Earth's crust.
• what are most metals found as?

  found as ores in the Earth's crust, which are often an oxide of the metal.
• extraction by reduction with carbon

  That a metal less reactive than carbon (eg. iron) can be extracted from its ore by reduction with carbon.

  -much CHEAPER than electrolysis
• extraction using electrolysis 


  electrolysis is used to extract metals that are more reactive than carbon.
• electrolysis of metal ores

  -electrolysis is used to extract metals, such as aluminium, from their ores if they're too reactive to be extracted by reduction with carbon.

  -aluminium oxide is dissolved in molten cryolite before electrolysis takes place, as this reduces the temperature at which it can be melted, and so reduces the cost.

  -during the electrolysis of aluminium oxide, ALUMINIUM is formed at the NEGATIVE electrode and OXYGEN is formed at the POSITIVE electrode.

  -the oxygen produced reacts with the carbon in the electrode to form carbon dioxide.
• Alternative Methods of Extracting Metals

  -supplies of some metal-rich ores are limited and traditional extraction techniques are damaging to the environment.

  -new methods of extracting metals from low-grade ores, and waste from traditional extraction, include bioleaching and phytoextraction, and the pros and cons associated with these methods.
• bioleaching 


  -bacterial method of extracting metals

  -uses bacteria which convert metal compounds in the ore into soluble metal compounds

  -separating metal from ore in the process

  -leachate (solution produced) contains metal ions, which can be extracted eg. electrolysis or displacement with a more reactive metal
• phytoextraction


  -growing plants in soil that contain metal compounds

  -metal compounds build up in leaves

  -plants then are harvested, dried and burned in a furnace

  -ash contains metal compounds

  -metal extracted by electrolysis or displacement reactions
• pros of bioleaching and phytoextraction?

  -cheap

  -much smaller environmental impact as they require less energy
• cons of bioleaching and phytoextraction?

  -they're slow

  -eg. in phytoextraction, it takes a long time for plants to grow and take up the metal
• recycling


  using waste materials to make new products
• advantages of recycling 


  conserves fossil fuels, as burning them contributes to acid rain and climate change

  -recycling conserves raw materials eg. metals on Earth

  -recycling prevents mining

  -recycling cuts down amount of rubbish sent to landfill-which pollutes the surroundings

  -recycling saves money as it is expensive to extract materials (needs energy)

  -recycling creates lots of jobs (transportation)
• life cycle assessment (LCA)

  assess the environmental impact of the entire lifetime of a product. The stages of the lifetime of the product can be seen as:

  -getting the raw materials

  -manufacturing and packaging

  -using the product

  -product disposal
• what are certain factors to be considered in a LCA?

  -how much water needed?

  -amount of energy needed?

  -amount of resources used?

  -amount of pollution produced?

  -how much waste is formed?

  -disposal of waste?
• getting raw materials LCA

  -damage local environment

  -extraction results in pollution due to high amounts of energy

  -transportation results in greenhouse gas emissions from combustion of fossil fuels

  -need to be processes so large amounts of energy needed

  -large amounts of waste which need to be disposed of

  -crude oil provides raw materials- but is non-renewable and supplies are decreasing
• manufacturing and packaging


  -can use a lot of energy and other resources

  -causes a lot of pollution eg. harmful fumes (carbon monoxide)

  -chemical reactions produce waste products

  -make sure polluted water isn't put back into environment
• using the product


  -can damage the environment

  -factors considered: how long a product is used, how many uses?

  -if product needs lots of energy to produce, but used for ages--> less waste and raw materials needed in the long run
• product disposal


  -energy is used to transport waste to landfill

  -pollutants released in atmosphere

  -landfill takes up space and pollutes land and water

  -if biodegradable, space taken up is temporary

  -incineration-burnt at very high temperatures -->used to generate electricity-->causes air pollution
• reactivity series


  places metals and some non-metals in order of their ability to form positive ions, and so their reactivity.
• the more reactive a metal is...

  the more easily it forms positive ions.
• how is the position of a (non) metal in the reactivity series detrmined?

  resistance of a metal to oxidation is related to its position in a reactivity series.
• metals at the TOP of the series?

  -most reactive

  -easily lose their electrons to form cations

  -gain oxygen (oxidised) more easily
• metals at the BOTTOM of the series?

  -less reactive

  -don't give up electrons to form cations as easily

  -more resistant to oxidation
• Carbon in the series?

  metal's position in the series compared to carbon dictates how it's extracted from it's ore
• How to work out the order of reactivity of metals?

  -compare relative reactivity of different metals with either an acid or water-->and put them in order from most reactive to least reactive

  -the metals higher in the series, lose electrons to form cations easily, so it reacts with water or acid more easily

  -OR you can measure the temperature change of the reaction with an acid or water over a set time period
• reaction of metals with dilute acids produces what?

  salts and hydrogen.
• the reaction of certain metals and water forms what?

  metal hydroxides and hydrogen.
• a more reactive metal will displace a...


  less reactive one in a compound.
• the products of reverse reactions can react to re-form what?


  the original reactants
• reversible reactions shown with what?

  shown with a double arrow
• haber process


  is an example of a reversible reaction and can reach dynamic equilibrium.
• dynamic equilibrium is when the rate of forward reaction equals the rate of backward reaction so there are no overall changes in concentration over time.
• in dynamic equilibrium, the concentrations of all substances remain constant because they are being produced at exactly the same rates as they are being used up.
• when a system reaches dynamic equilibrium, it means that the forward and backwards reactions occur at equal speeds.
• Le Chatelier's Principle


  states that if you change the conditions of a reversible reaction the system will react to counteract that change by shifting the position of equilibrium.
• increasing the temperature of a reversible reaction will move the position of equilibrium in the...

  ENDOTHERMIC direction