GCSE Chemistry Notes: Explaining oxidation-reduction and the chemistry of rusting
RUSTING-CORROSION and an introduction to OXIDATION and REDUCTION
Doc Brown's Chemistry KS4 Science GCSE/IGCSE Chemistry Revision Notes
2. Corrosion of Metals e.g. iron & introducing redox reactions – In particular, the rusting of iron and corrosion prevention
What is an oxidation reaction? What is a reduction reaction? What do we mean by a REDOX reaction? How do we write oxidation/reduction equations? Why is rusting an oxidation? What is an oxidising agent? What is a reducing agent? What do you mean by the corrosion of metals? What is chemically happening when iron rust? How can we prevent iron from rusting? What is stainless steel? What is galvanising? What is an oxidation reaction? What is a reduction reaction? This page also includes an introduction to REDOX reactions. These revision notes on oxidation & reduction, balanced symbol equations and rusting corrosion of metals and its prevention, should prove useful for the new AQA, Edexcel and OCR GCSE (9–1) chemistry science courses.
Its a good idea to study the theory of oxidation & reduction before reading the technical details of rusting and rust prevention.
EQUATION NOTE: The equations are often written three times: (i) word equation, (ii) balanced symbol equation without state symbols, and, (iii) with the state symbols (g), (l), (s) or (aq) to give the complete balanced symbol equation.
Associated KS4 Science GCSE/IGCSE Chemistry notes pages: The Periodic Table * Group 1 Alkali Metals * Metal extraction * Transition metals * Alloys–uses of metals * Electrochemistry * Rates of Reactions (e.g. metal–acid) * Easy KS3 science multiple choice quiz start on metal reactivity and KS3 word–fills and GCSE m/c QUIZ on metal reactivity : Foundation Level or Higher Level & GCSE/IGCSE reactivity word–fill or Rusting word–fill
Advanced Level Chemistry Redox Reaction
Notes (for Advanced level chemistry students only!)
chemistry revision notes:
basic school chemistry science GCSE chemistry, IGCSE chemistry, O level
& ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old
science students for national examinations in chemistry for topics including the
reactivity series of metals
chemistry revision notes: basic school chemistry science GCSE chemistry, IGCSE chemistry, O level & ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old science students for national examinations in chemistry for topics including the reactivity series of metals
2A METAL CORROSION and the RUSTING of IRON and its PREVENTION
Corrosion is the destruction of materials (metal, stone etc.) by chemical reactions with substances in the environment.
Most metals corrode - chemically attacked, when in contact with oxygen and water.
The rusting of iron is an example of corrosion.
Rusting, like any other corrosion, involves oxidation and reduction - redox reactions.
The more reactive a metal, the more easily it is oxidised - the more easily the metal atoms lose electrons to form a positive ion.
Both air (oxygen source) and water are necessary for iron to rust - need to know experiment to show this.
Corrosion by rusting can be prevented by applying a coating that acts as a barrier to air and water, such as greasing, painting or electroplating.
In the case of the metal aluminium, this has an oxide coating that protects the metal from further corrosion.
Some rust prevention coatings are reactive and may contain corrosion inhibitors or a more reactive metal
Magnesium blocks can be attached to steel ships to provide sacrificial protection, but the blocks have to replaced when corroded away.
The RUSTING PROCESS
An experiment to investigate sacrificial corrosion
Corrosion and the use of other metals
2B OXIDATION & REDUCTION – REDOX REACTIONS –
An INTRODUCTION for GCSE/IGCSE/O Level students
The oxidation reactions you are most likely to come across at first in your chemistry course are the reaction of metals with oxygen e.g. by heating a strip of metal in a strongly in a bunsen flame.
The metal is considered to be oxidised because the metal gains and combines with oxygen atoms from the oxygen molecules in air e.g.
(i) magnesium + oxygen ===> magnesium oxide
(ii) copper + oxygen ===> copper oxide
The opposite of oxidation is reduction and one simple definition of it is oxygen loss (opposite of oxidation above!).
You most likely to come cross this first when studying the extraction of metals from a metal oxide (maybe as an ore)
For example, if you strongly heat a mixture of copper oxide with carbon (charcoal or graphite powder) you find bits of brown–orange copper are formed.
For more details see of some of these reactions see notes on the
Advanced Level Chemistry Redox Reaction Notes (it repeats this introduction and then moves on!)
Definition reminders and lots more EXAMPLES of OXIDATION and REDUCTION
In the examples in the first double column section below, the equations are not meant to be complete or balanced.
What I've highlighted, is the chemical change that fits the definition of oxidation and reduction,
OXIDATION – definition and examples
(based on oxygen gain OR electron loss transfer)
REDUCTION – definition and examples
(based on oxygen loss OR electron gain transfer)
Oxidation is the gain or addition of oxygen by an atom, molecule or ion
(1) S ==> SO2 [burning sulphur – oxidised]
(2) CH4 ==> CO2 + H2O [burning (oxidation) of methane to water and carbon dioxide, C and H gain O]
(3) NO ==> NO2 [nitrogen monoxide oxidised to nitrogen dioxide]
(4) SO2 ==> SO3 [oxidising the sulphur dioxide to sulphur trioxide in the Contact Process for making sulphuric acid]
Reduction is the loss or removal of oxygen from a compound etc.
(1) CuO ==> Cu [loss of oxygen from copper(II) oxide to form copper atoms]
(2) Fe2O3 ==> Fe [iron(III) oxide reduced to iron in blast furnace]
(3) NO ==> N2 [nitrogen monoxide reduced to nitrogen, catalytic converter in car exhaust]
(4) SO3 ==> SO2 [sulphur trioxide reduced to sulphur dioxide]
Oxidation is the loss or removal of electrons from an atom, ion or molecule
the balanced half equations
(1) Fe ==> Fe2+ + 2e– [iron atom loses 2 electrons to form the iron(II) ion, start of rusting chemistry]
(2) Fe2+ ==> Fe3+ + e– [the iron(II) ion loses 1 electron to form the iron(III) ion, also part of rusting chemistry]
(3) 2Cl– ==> Cl2 + 2e– [the loss of electrons by chloride ions to form chlorine molecules e.g. in electrolysis]
Reduction is the gain or addition of electrons by an atom, ion or molecule
e.g. the balanced half equations
(1) Cu2+ + 2e– ==> Cu [the copper(II) ion gains 2 electrons to form neutral copper atoms, electroplating or displacement reaction)
(2) Fe3+ + e– ==> Fe2+ [the iron(III) ion gains an electron and is reduced to the iron(II) ion]
(3) 2H+ + 2e– ==> H2 [hydrogen ions gain electrons to form neutral hydrogen molecules, electrolysis of acids or metal–acid reactions]
oxidising agent is the species that gives the oxygen
to an atom, ion or molecule
an oxidising agent accepts electrons i.e. an oxidising agent removes electrons from some atom, ion or molecule.
In either process the oxidising agent gets reduced.
reducing agent is the species that removes the oxygen
from an atom, ion or molecule
a reducing agent acts as the electron donor i.e. it gives electrons to some atom, ion or molecule.
In either case the reducing agent gets oxidised.
REDOX REACTIONS – in a reaction overall, BOTH oxidation and reduction must go together
(g) Redox reaction analysis based on the oxygen definitions of oxidation and reduction
(h) Redox reaction analysis based on the electron definitions of oxidation and reduction
Miscellaneous Extra Redox Notes
Advanced Level Chemistry Redox Reaction Notes (it repeats this introduction and then moves on!)
OTHER ASSOCIATED PAGE LINKS
and GCSE/IGCSE m/c QUIZZES on metal reactivity
KS4 Science GCSE/IGCSE/O level Chemistry revision notes pages:
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