topic 4 extracting metals and equilbria

• reactivity

  • reactivity series ( potassium , sodium , calcium , magnesium , aluminium , carbon , zinc , iron , tin , lead , hydrogen , copper , silver , gold , platiumum
  • reaction with water / dilute HCl - potassium , sodium , calcium , reacts with cold water to form hydrogen and a metal hydroxide - reacts viloently
  • reaction with water / dilute HCl - magnesium , aluminium , zinic , iron reacts very slowly with cold water , but with steam reacts to form hydrogen and metal oxide , not violently but reacts to form products
  • copper silver and gold does not react with steam water or HCl
• reactions

  • metal + water -> metal hydroxide + hydrogen ( K, Na , Ca )
  • metal + steam -> metal oxide + hydrogen (Mg, Al , Zn , Fe )
  • metals + dilute acid -> salt + hydrogen ( Mg , Al ,Zn , Fe )
• displacement reactions / redox reaction

  • when a more reactive element displaces from one of its compounds
  • displacement reactions are also REDOX REACTIONS as one substance is being reduced ( gain of electrons / loss of electrons ) and other is being oxidised ( loss of electrons / gain of oxygen )
• ores

  • are rocks that contain enough of a compound to extract for a profit
  • few metals such as silver and gold can not be ores as they are not reactive enough to become compounds so found in native state
• metal - reactivity - extraction

  • potassium , sodium , calcium , magnesium , aluminium - extracted by electrolysis - being more reactive than carbon
  • zinc , iron , tin , lead , copper - extracted by heating with carbon - less reactive than carbon
  • silver , gold , platiumum - found as an uncombined element
• extracting metals from its ores

  • some metals can be extracted by heating their compound with carbon ( due to it being less reactive )
  • other metals are extracted from their compound by electrolysis as a molten compound ( due to having a higher reactivity than carbon)
• metal extraction is reduction

  • reduction is the gain of the electrons but also the loss of oxygen
  • to obtain metals from their oxides , oxgyen would be need to removed
  • the removal of oxygen is a reduction reaction as the metal oxide is loosing oxygen
• electrolysis of aluminium oxide

  • aluminium oxide is dissolved with molten cryolite to decrease melting point - to make it more cheaper
  • made of carbon electrodes
  • postivive electrodes are submerged into electrolyte
  • negatie cathode is lined around the container ,
  • when aluminin gains electrons at the cathode the metal settles at the bottem due to higher density than soultion
• biological methods of metal extractions - copper

  • phytoextraction - advantages cheaper than electrolysis , when buring can be used to produce energy - disadvantage burning plants releasing ghg
  • bioleaching - advantage does not require high temp , disadvantage toxic substances' can be produced damaging the environment
  • both - adv causes less harm to landscape , dis very slow
• corrosion of metal is oxidation

  • corrosion happens to the surface of metal , changes by reaction of oxygen
  • metal gains oxygen
  • more reactive the metal the more likely it's going to corrode , gain oxygen
• recycling

  • advantages - natural resevres of metal ores last longer
  • , less energy ( cheaper ) to recycle
  • reduces need to mine ( mining causes damage to landscape)
  • less polulution - some metal extractions release ghg , sulphur dioxide
  • disadvantages - cost of collection , sorting , transporting metals can be expensive , long process to sort metals
• properties of metals

  • general properties - shiny , conduct heat , conduct electricity , malleable ( can be hammered into different shapes ) , ductile ( can be stretched into wire )
  • different metals have slightly different properties
• properties - Al

  • low density
  • does not corrode - protective layer of Al2O3 formed on surface quickly
  • used to make aeroplanes due to low density
• properties - Cu

  • good electrical conducto - used to make electrical cables
  • has low reactivity and does not react with water - used in water pipes
• properties - iron + steel

  • iron is cheap to extract - uses carbon to extract
  • iron very soft - made into its alloy steel
  • steel used to make bridges , cars , electrical goods , frames for buliding
  • both iron and steel rust - iron reacts with water and oxygen ( oxidises )
• alloys

  • metals are mixed with other metals to obtain a better property
  • converting pure metals into alloys increases their strength
  • in pure metals all atoms are same size meaning it requires little energy to slide atoms
  • in an alloy there is different size of atoms in the mixture , meaning it requires more energy to slide past each other making it harder and stronger
• example of alloys

  • iron - iron rusts
  • can be maded into alloy stainless steel ( mixture of iron and small amounts of chromium and nickel )
  • gold - pure gold is too soft to be used in jewellery
  • other metals , copper and silver are added to make a harder and stronger alloy
  • the purity of gold is measured in carats or fineness - pure gold is 24 - carat and has a fineness of 1000 parts per thousand
  • the lower the carat and fineness , the lower the purity of gold
• shape memory alloys

  • Nitinol is an alloy of nickel and titanium
  • it is a smart material - it has the property that changes with a change in conditions ( usually temperature )
  • nitinol is a shape memory alloy - if the shape of something made in nitinol is altered , it returns to its original shaped when heated
  • nitinol is used to repair of a collapsed artery : doctors slide a squished nitinol tube into damaged artery
  • as it warms up due to body heat , tube returns to original shape
  • holding artery open
• dynamic equilibrium

  • reversible reaction ( go both ways ) are able to reach a state of dynamic equilibrium
  • forward reaction and backward reaction are happening at the same rate
  • the concentration of reactants and products do not change
  • equilibrium can lie to the left or the right ... if ..
  • lies to the right - there are more products than reactants
  • lies to the left - there are more reactants than products
  • the exact position depends on the conditions ( eg temperature , pressure , concentration )
• Le Chatelier's Principle

  • the position of the equilibrium will shift to oppose any changes
• Le Chatelier's Principle - example

  • all based on eg N2 + 3H2 --> 2NH3
  • if temperature increase, favours endothermic , so equilibrium shifts left - opposite occurs when temp decrease , favours exothermic reaction , shifts to right
• Le Chatelier's principle

  • if pressure increase , favours side with fewer moles of gas , so equilibrium shifts right , opposite occurs when pressure decrease , favoures side with more moles of gas , shifts to left
  • if the moles of the gass are the same on boths sides equilibrium wont shift
  • if the reactants is added ( increase concentration ) ,equilibrium shifts to right
  • if the products is added ( increases concentration ) , equilibrium shifts to the left
  • decreasing concentration or removing a chemical will have the opposite reaction
• optimal conditions for haber process - production of ammonia

  • to maximies yeild , should use low temp , to favour forward exothermic reaction , this will decrease rate
  • a comprimise of 450 c is used
  • to maximise yeild , should use high pressure , to favour forward reaction as there are less moles on product side , however expensive equipment is needed and alot of energy to maintan pressure
  • as comprimise 200 atmosphere is used
  • catalyst is used - increases the rate and reduces energy needed
• equilibrium shifts can also be results in changes in colour

  • 2HI(colourless) <-> (reversible) H2 + I2 ( purple )
  • if H2 is added equilibrium will shift to left as concentration increase on product side, yield will decrease of I2
  • if H2 is removed , equilibrium will shift to right as concentration of product side has decrease , to accommodate equilibrium shifts to right increasing yield of I2