Chapter 9 - Metals
Metal reaction with acid
- Produces hydrogen and metal salt
- Example : 2HCl + Mg -> MgCl2 + H2
- Rate of hydrogen production can be compared with other metals to form reactivity series.
Metal reaction with air/oxygen
- Metals react with oxygen to form metal oxides
Metal reaction with cold water/steam
- Reactive metals react with cold water to produce metal hydroxide and hydrogen gas
- Moderately reactive metals react rapidly with steam compared to cold water to form metal oxide and hydrogen gas
Uses of aluminium (3 points)
1) Manufacture of aircraft because of low density
2) Overhead Electrical cables because of its low density and good electrical conductivity
3) Food containers because of its resistance to corrosion
Uses of copper (1 point)
1) Electrical wiring because of its good conductivity and ductility.
Brass composition
Copper and Zinc
Stainless steel composition
Iron and other elements like chromium, nickel, carbon
Alloys compared to metals (2 points)
- More harder and stronger
- More useful
Use of stainless steel
- Cutlery because of its hardness and resistance to rusting
How are alloys harder than pure metals
- Alloys consist of different-sized atoms, which means the layers cannot slide over each other. This makes them harder and stronger than pure metals.
Reactivity Series
Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Hydrogen, Copper, Silver, Gold.
Please send cats, monkeys and calm zebras into hot countries. Silver Gold :(
Unreactivity of aluminium
- Even though aluminium is high in the reactivity series, it has a protective oxide layer coating on its surface which forms when it is manufactured.
Displacement reaction
In a displacement reaction, a more reactive metal with displace the less reactive metal from a solution of its salt.
There is also a redox that occurs. Eg: Zn + Cu(2+) -> Zn(2+) + Cu
Rusting of iron
- Needs oxygen and water to occur
- Forms hydrated iron(III) oxide.
Galvanising
- Zinc is used in galvanizing as a barrier and sacrificial protection of iron or steel
How does galvanising work
- Sinze zinc is more reactive than iron, it will lose electrons to the iron, therefore protecting it. This is because zinc is higher in the reactivity series and forms ions easier than iron.
Ease of extraction of metals
- Metals higher in reactivity series are harder to extract than those lower.
Iron extraction
Extracted from hematite in blast furnace
Aluminium extraction
Electrolysis of bauxite (aluminium oxide)
Blast furnace (5 steps)
1) Burning of coke -> carbon dioxide
C + 02 -> CO2
2) Reduction of CO2 to CO
CO2 + C -> 2CO
3) Reduction of iron(III) oxide by CO
Fe2O3 + 3CO -> 2Fe + 3CO2
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Extra steps to form slag
4) Thermal decomposition of calcium carbonate to form calcium oxide
CaCO3 -> CaO + CO2
5) Slag formation
CaO + SiO2 -> CaSiO3
Electrolysis of Bauxite
Cathode : Al(3+) + 3e -> Al
Anode: 2O(2-) -> O2 + 4e
Cryolite is used to lower the melting point of aluminum
Carbon anodes need to be regularly replaced because oxygen reacts with carbon to form CO2.