Oxidation is the addition of oxygen or the removal of hydrogen. An
oxidising agent is a substance that adds oxygen to or removes hydrogen from another substance. Burning, respiration and rusting are common examples of oxidation.
|S(s) + O2(g) → SO2(g)||Sulphur is oxidised to sulphur dioxide by the addition of oxygen|
|H2S(g) + Cl2(g) → 2HCl(g) + S(s)||Hydrogen sulphide is oxidised to sulphur by the removal of hydrogen|
Copper is a metal which is extracted by heating copper oxide with carbon. The equation for this reaction is:copper oxide + carbon → copper + carbon dioxide
Name the substance that is oxidised during this reaction.
Explain your answer.
Carbon is oxidised because it gains oxygen.
Reduction is the removal of oxygen or the addition of hydrogen. A
reducing agent is a substance that removes oxygen from or adds hydrogen to another substance. Extraction of metals from their oxide ores is a common example of reduction.
|N2(g) + 3H2(g) → 2NH3(g)||Nitrogen is reduced to ammonia by the addition of hydrogen|
|PbO(s) + H2(g) → H2O(g) + Pb(s)||Lead oxide is reduced to lead by the removal of oxygen|
Redox is short for REDuction and OXidation. A redox reaction is a reaction in which oxidation and reduction takes place at the same time. One substance is oxidised while the other is reduced.
PbO(s) + H2(g) → H2O(g) + Pb(s)
In the reaction above it can be noted that;
- Lead oxide (PbO) is reduced to lead (Pb)
- Hydrogen (H2) is oxidised to water (H2O)
- Hydrogen is the reducing agent because it removed oxygen from the lead
- Lead Oxide is the oxidising agent because it added oxygen to the hydrogen
NB The reducing agent is itself oxidised in the process of reducing another substance while the oxidising agent is reduced in the process in the process of oxidising another substance.
Redox in terms of electron loss and gain
Oxidation and reduction can also be explained in terms of the movement of electrons.
Oxidation is the removal of electrons whilst reduction is the addition of electrons
An oxidising substance removes electrons from another substance
A reducing agent adds electrons to another substance
Redox ionic equations
Ionic equations can be used to show whether a substance has been reduced or oxidised. Lets take the lead oxide reduction as an example and create ionic equations.
PbO(s) + H2(g) → H2O(g) + Pb(s)
- Write down the equation in form of ions of the reactants and the products. Leave the free elements without charges
- Remove the ions whose charges remain the same on both sides of the equation. These are called spectator ions.
- Now as you can see, the positively charged Pb2+ ion gained two electrons to become the neutral Pb atom
- … also the neutral H2 lost two electrons to become positively charged 2H+ ions
Pb2+ O2- + H2(g) → 2H+ O2- + Pb(s)
O2- + H2(g) → 2H+ O2- + Pb(s)
This gives us
Pb2+ + H2(g) → 2H+ + Pb(s)
That is reduction and the ionic half-equation for that is
Pb2+ + 2e2- → Pb
That is oxidation and the ionic half equation for that is
H2 – 2e–→ 2H+
H2 → 2H+ + 2e–
Extraction of Iron
Iron is extracted from iron ore by a process of reduction in the blast furnace. The main ores of iron are haematite (Fe2O3) and magnetite (Fe3O4). Carbon is used as a reducing agent.
Raw materials of the process are:
- Iron ore such as hematite which is mainly iron(III) oxide, Fe2O3
- Limestone which is mainly calcium carbonate, CaCO3
- Coke which is almost pure carbon, C
- Hot air which contains oxygen
Iron ore, limestone and coke are mixed to give a mixture called charge. Charge is fed into the top of the blast furnace. Hot air is fed through the tuyeres near the bottom of the furnace.
The reactions occur as follows:
- Near the base of the furnace
- Middle of the furnace
- Top of the furnace
- Formation of slag
The blast of hot air oxidises the carbon in coke to carbon dioxide.
C (s) + O2 (g) → CO2 (g)
The carbon dioxide reacts with more coke to produce carbon monoxide.
C (s) + CO2 (g) → 2CO (g)
The iron(III) oxide is reduced by carbon to form Iron and carbon monoxide (Direct reduction).
Iron(III) oxide + carbon → iron + carbon monoxide.
Fe2O3 (s) + 3C (s) → 2Fe (l) + 3CO (g)
Carbon monoxide reacts with the Iron (III) oxide iron and cabon dioxide (Indirect reduction).
Iron(III) oxide + carbon monoxide → iron + carbon dioxide
Fe2O3 (s) + 3CO (g) → 2Fe (l) + 3CO2 (g)
The liquid iron trickles to the bottom of the furnace.
The limestone is broken down by the heat in the furnace to produce calium oxide and carbon dioxide.
CaCO3 → CaO (s) + CO2 (g)
The calcium oxide then reacts with the sandy impurities (Silicon dioxide) in the iron to form slag (Calcium oxide).
calcium oxide + silicon dioxide → calcium silicate
CaO (s) + SiO2 (s) → CaSiO3 (s)
The calcium silicate forms a slag which runs down the furnace and floats on the iron.
Iron is extracted from iron ore by reduction in a blast furnace. Limestone is added to the blast furnace to separate impurities from the iron.
- Name two other raw materials which are added to the blast furnace………. 
- Explain what is meant by reduction. ……..
- Coke and hot air
- Reduction is the removal of oxygen from a substance or the addition of hydrogen to a substance
Basic oxygen-lance furnace
Iron from the blast furnace is called cast iron or pig iron. It contains many impurities such as carbon, sulphur and phosphorus. It is purify in the oxygen-lance furnace where oxygen is blown into the molten iron at high pressure to oxidise the
Pure iron is no good as a structural material because it is too soft, and stretches quite easily and also because it rusts very easily.
Adding small amounts of other elements produces an alloy of iron called steel. An alloy is a mixture of a metal and other elements. Alloys have many desirable properties not found in pure metals.
Some alloys of iron
Adding a very small amount of carbon to iron produces mild steel which is hard and strong. It is used for buildings, ships, car bodies, and machinery.
Adding nickel and chromium to iron produces stainless steel which is hard and rustproof. It is used for cutlery, and equipment in chemical factories.
Typical compositions are:
mild steel – 99.7% iron and 0.3% carbon
stainless steel – 70% iron, 20% chromium, and 10% nickel
Globally Harmonized System of Classification and Labelling of Chemicals (GHS) pictogram for oxidizing substances