SC4: extracting metals and equilibria Flashcards
the more reactive a metal is…
the more vigorous its reactions are
the more easily it loses electrons in reactions to form cations
metal + water
metal hydroxide + hydrogen
metals that react quickly with cold water are…?
very reactivr
metal + steam
metal oxide + hydrogen
how do metals that react slowly with cold water react with steam?
quickly
what happens in the reactions of metals with water, steam and acids?
-the metals lose electrons and form cations
-the metal is oxidised and the water is reduced
which metals don’t react with dilute acids?
metals below hydrogen in the reactivity series
what happens in the reactions of metals with water, steam and acids?
-the metals lose electrons and form cations
-the metal is oxidised and the water is reduced
-hydrogen is produced
how does reactivity affect metals tendency to form cations?
-the higher up a metal, the more likely to form cations
-the lower down a metal, the more likely to resist oxidation
displacement reaction
a reaction in which a more reactive element displaces a less reactive element from an aqueous solution of the latter’s ions
how can the reactivity series be deduced?
by doing several displacement reactions; a piece of metal is dipped into a salt solution, different combinations of metal and salt solution are tested
what does it mean if something has been coated in a displacement reaction?
the metal reacting with the solution has displaced it
spectator ions
ions that do not participate in a reaction
redox reaction
an oxidation reaction paired with a reduction reaction
what do metals with a higher reactivity than hydrogen do in displacement reactions?
the displace hydrogen from acids
ore
a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile
low grade ores vs high grade ores
-low-grade ores = small percentage of the metal or its compound
-high-grade ores contain a larger percentage
how are unreactive metals found?
they are found in the earth as the metal itself
why isn’t electrolysis used to extract all metals?
large amounts of electrical energy are needed so it’s expensive
how is a metal extracted if it’s less reactive than carbon?
heating with carbon
metal oxide + carbon
metal + carbon dioxide
extracting iron
-as iron is below carbon in the reactivity series it can be displaced from its compounds by heating with carbon
-iron is extracted from iron ore in a a blast furnace
-iron(III) oxide is reduced to molten iron when it reacts with carbon
how are metals higher than carbon extracted?
electrolysis
how is impure copper purified?
electrolysis
what are electrolytes?
ionic compounds in the molten state or dissolved in water
what are electrodes?
charged metal plates
cathode
negative electrode
anode
negative electrode
what happens at the cathode & anode in electrolysis?
cathode: metal ions gain electrons & form an atom
anode: substance loses electrons & forms a gas
electrolysis of aluminium oxide
-aluminium oxide is insoluble in water, so it must be molten
-the melting point of aluminium oxide is high, a lot of energy must be transferred to break its strong ionic bonds, and this is expensive
-to reduce costs, powdered aluminium oxide is dissolved in molten cryolite
-this ionic compound melts at a lower temperature than aluminium oxide, reducing costs
-both electrodes are made of graphite
-at the cathode, aluminium ions gain electrons and form aluminium atoms
-at the anode, oxide ions lose electrons and form oxygen gas
steps of recycling metals
- collecting and transporting the used items to a recycling centre
- breaking up and sorting the different metals
- removing impurities from the metals
(the metals can then be used to manufacture new metal items)
advantages of recycling metals
- more economic - less energy is needed to produce a metal
- less damage to the environment - fewer quarries and mines, less noise and less heavy traffic
- saves valuable raw materials - reserves of metal ores will last longer
disadvantages of recycling
-the collection and transport of used items needs organisation, workers, vehicles and fuel
-it can be difficult to sort different materials from one another
simple way to separate aluminium from iron
a magnet or electromagnet will attract iron but not aluminium
why is a life cycle assessment (LCA) carried out?
carried out to assess the environmental impact of products
main stages of a LCA
- obtaining the raw materials needed for manufacture
- manufacturing the product
- using the product
- disposing of the product at the end of its useful life
impact of raw materials (LCA)
-using up limited resources such as ores and crude oil
-damaging habitats through quarrying, mining, or felling trees
impact of manufacture (LCA)
using up land for factories the use of machines and people
impact of use (LCA)
-the impact of a product on the environment during its use depends on the type of product
-for example, a wooden chair has very little impact, unless it needs cleaning or repair
-on the other hand, a car will have a significant impact
impact of disposal (LCA)
-using up land for landfill sites
-whether any or all of the product can be recycled or reused
phytoextraction steps
- plants are grown on a low-grade ore that contains lower amounts of metal
- the plants absorb metal ions through their roots and concentrate these ions in their cells
- the plants are harvested and burnt
- the ash left behind contains a higher concentration of the metal than the original ore
- the ash is processed to obtain the metal
phytoextraction advantages & disadvantages
advantages
-reduces the need of mining
-conserves limited supplies of valuable ores
disvantages
-slow
quarries
-large holes in the ground for mining
-create noise, dust and traffic
-destroy natural habitats
biobleaching
-certain bacteria can break down low-grade ores to produce an acidic solution (leachate) containing metal ions
-iron is used to displace copper from the leachate
-because iron is cheaper than copper, it’s cost effective
biobleaching advantages and disadvantages
advantages:
-can extract copper
-doesn’t need high temps
-cost effective
disadvantages:
-produces toxic substances (eg sulfuric acid) which damage the environment
reversible reaction
the products can be changed back into the reactants
dynamic equilibrium
-the proportions of reactants and products stay the same
-the term ‘dynamic’ emphasises that the forward and the backward reactions continue to occur (at the same rate)
when can dynamic equilibrium happen?
in a closed system
haber process
an industrial process for producing ammonia from nitrogen and hydrogen by combining them under high pressure in the presence of an iron catalyst
haber process steps
- nitrogen (extracted from the air) and hydrogen (obtained from natural gas) are pumped through pipes
- a compressor increases the gas pressure to 200 atmospheres
- the pressurised gases are heated to
450°C and passed through a reaction chamber containing an iron catalyst to speed up the reaction - the reaction mixture is cooled so that ammonia liquefies and can be removed
- unreacted nitrogen and hydrogen are recycled
how can an equilibrium position
be changed?
-change temp, pressure or concentration
changing pressure in equilibrium
if the pressure is increased, the equilibrium position moves in the direction of the fewest molecules of gas
changing concentration in equilibrium
if the concentration of a solute (thing dissolved) is increased, the equilibrium position moves in the direction away from this solute
changing the temperature in equilibrium
-in a reversible reaction, if the reaction is exothermic in one direction, it is endothermic in the other direction
-if the temperature is increased, the equilibrium position moves in the direction of the endothermic process
exothermic
releases energy/heat
endothermic
absorbs heat/energy
what does the temp used in a
reversible reactions depend on?
-low enough to get an acceptable yield
-high enough to do this in an acceptable time
what does pressure used in reversible reactions depend on?
-low enough to keep costs down
-high enough for achievable yield
