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Chemistry revision Topic 4: Obtaining and Using metals (Displacement…
Chemistry revision Topic 4: Obtaining and Using metals
Ways to find out reactivity:
Metal+water->metal hydroxide+hydrogen
Group 1 and 2, very reactive
Exothermic reaction
Metal+salt solution
Iron+copper sulphate->iron sulphate+copper
More reactive metal will replace less reactive metal in salt solution
Acid+metal->salt+hydrogen
More reactive:
Quicker and more bubbling from hydrogen
Louder pop if you do the test for hydrogen
Displacement reactions:
Redox reaction as both reduction and oxidation takes place
O
xidation
i
s
l
oss (of electrons),
R
eduction
i
s
g
ain (of electrons)
More reactive metal displaces less reactive metal in salt solution
Zinc+copper sulphate->zinc sulphate+copper
Zinc loses 2 electrons so is oxidised
Copper gains 2 electrons so is reduced
Reactivity series:
Most metals extracted from ores (rock containing metal:oxide of ,metal) found in earth's crust
Unreactive metals are found in the earth's crust uncombined, and are refined before used
Extraction of metal:
Less reactive than carbon=
Reduction(in terms of oxygen) with carbon:
Iron oxide+carbon->carbon dioxide+iron
Carbon has been oxidised as it has gained oxygen
Iron has been reduced as it has lost oxygen
More reactive than carbon=
Electrolysis:
Bauxite (aluminium oxide) dissolved in molten cryolite(less common ore of aluminium) to reduce melting point, making it cheaper
Aluminium goes to cathode and gets 3 electrons. Aluminium sinks to bottom
Oxygen goes to anode and loses 2 electrons
Some oxygen reacts with carbon, producing carbon dioxide, eating away electrode.
Resistance to oxidation
More reactive
Less resistant to oxidation
Less resistant to corrosion
Less reactive
More resistant to oxidation
More resistant to corrosion
Oxidation is gain (of oxygen), Reduction is loss (of oxygen)
Alternative extracting methods:
Bioleaching:
Uses bacteria to convert metal compounds in the ore into soluble metal compounds(separating the metal from the ore)
The
leachate
(solution produced by process is extracted for the metal ions (electrolysis or displacement
Phytoextraction
Growing plants in soil that contains metal compounds
Metal compounds build up in leaves
Plant can be harvested, dried and burned in a furnace to get ash which contains metal compounds which can be extracted (electrolysis or displacement)
Advantages:
Cheap as it uses less energy
Smaller environmental impact
Protects habitats as earth doesn't need to be dug up, shifted or disposed to obtain or
Disadvantage:
Slow(e.g. plants need to grow)