last updated 23rd Jan 2014
Metals have different reactivity and you need to be familiar with the “ranking” of metals according to their ability to react. We call this the reactivity series of metals.
From the most reactive to the least reactive metals, the sequence is
- Carbon, (used to check the reduction of metal oxides)
- Hydrogen, (used to check the displacement of H+ ions in acids)
Carbon and Hydrogen are not metals but are placed in the series as a form of reference. With Carbon above zinc, it serves as a reminder that carbon can reduce any metal oxides found below Zinc. Carbon cannot reduce any metal oxides above zinc.
Because of their strong reactivity, the reactive metals are commonly found in the form of a compound.
It is not easy to find a reactive metal existing as an element. Reactive metals tends to lose electrons easily to form ions/compounds.
Whichever of the 2 metals which becomes atoms, is the least stable and vice versa.
The opposite is true for non-reactive metals. They are common found existing in the form of elements as they are relatively stable and do not tend to lose electrons easily.
You need to be familiar with a few metal reactions.
(a) Metal + Oxygen,
(b) Metals + water,
(c) Metals + Steam,
(d) Metal + Acids,
(e) Metals + solutions of salts,
(f) Metal Oxides + Carbon/hydrogen,
Different metals react with oxygen to give different colored flames. Potassium (lilac), sodium (yellow), calcium (red), magnesium (white).
Aluminium does not react with oxygen because it is naturally coated with a layer of oxide. When the layer is removed, a white oxide layer can be seen forming and the metal gets hot.
Zinc and iron fillings glow when heated with air but they do not catch fire.
Iron occurs naturally as iron oxide (Fe2O3 hematite) or magnetite (Fe3O4), Zinc occurs naturally as Zinc Sulfide (ZnS)
Metals can be extracted from its compound by various methods (a) electrolysis, (b) reduction, (c) displacement
Electrolysis is used to extract very reaction metals like K, Ca, Na, Mg, Al
Other metals can be extracted by reduction using carbon, hydrogen, carbon monoxide.
Zinc can only be reduced by carbon. It cannot be reduced by hydrogen.
Iron and Blast Furnace
Haematite, coke and limestone added at the top of blast furnace.
Carbon reacts with oxygen to produce carbon dioxide and a lot of heat.
Carbon dioxide further reacts with carbon to produce carbon monoxide.
Carbon monoxide reduces the hematite.
Calcium carbonate undergoes thermal decomposition and forms calcium oxide.
Impurities in the hematite such as sand will react with calcium oxide to form calcium silicate. This is a type of base and acid reaction.
Calcium silicate forms a layer over the molten iron.
Slag is used in road making and as “slag cement” – a final ground slag which can be used in cement, often mixed with Portland cement.
- C + O2 —> CO2 + Heat
- CO2 + C —> 2CO
- Fe2O3 + 3CO —> 2Fe + 3CO2
- CaCO3 —> CaO + CO2
- SiO2 + CaO —> CaSiO3 (slag or calcium silicate)
Steel is an alloy mainly consisting of iron and carbon. The carbon content can vary to give carbon steel with different physical properties.
Stainless steel can be made by adding other metals into the mixture of iron and carbon.
Different Types of Steel
- cast iron
- wrought iron
- mild steel
- high carbon steel
- stainless steel
- titanium steel
- manganese steel
||% of Carbon
|| less than 0.2%
||car bodies, machinery, cables,nails, chains
||between 0.2% – 0.6%
||tougher and harder than mild steel
||steel girders, rails
|high carbon steel
||0.6% – 1.5%
||tough and hard but brittle
||chromium and nickel
||corrosion resistance and acid resistant
A metal is coated over another metal to prevent the underlying metal from corrosion. E.g. metal A coated over metal B and metal B will not corrode. The metal coating must be more reactive than the underlying metal.
e.g. zinc coated over iron : since is zinc is more reactive, zinc corrodes and iron remains unreacted.
Other methods of corrosion prevention
Coat a layer of oil or grease, paint or plastic over iron. This prevents air and water from reacting with the iron.
Coat a layer of less reactive metal over iron. e.g Tin plating
Underground sewage steel pipes are protected from rusting by attaching blocks metal with higher reactivity (e.g. magnesium) to them. The magnesium protects the pipes from corroding as magnesium is more reactive.