CH5 Revision Aid

This is provided by WJEC on their website but I'm sure it links in with topics done by other exam boards. I find this a very useful tool when revising, I like to make notes and it helps me give my notes a very good structure. There are a few mistakes in there so I use it after I know the topics and I'm confident about the chemistry behind it. Hope you enjoy it!

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  • Created by: lava-mite
  • Created on: 21-02-13 18:21
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GCE in Chemistry



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UNIT CH5 Physical and inorganic chemistry
This unit develops ideas of redox, kinetics, energy changes and equilibria.
The inorganic chemistry of some elements in various sections of the Periodic Table is studied.

Topic 15
15.1 Redox and standard electrode potential

15.2 Redox reactions

15.3 Applications

Topic 16

16.1 General…

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Topic 15
Topic 15.1 Redox and standard electrode potential
Topic 15.2 Redox reactions
(a) Redox
Candidates should be able to:
describe redox in terms of electron transfer, use oxidation states (numbers) to identify
redox reactions and decide which species have been oxidised and which reduced;

Oxidation may be defined…

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3Cl2(g) + 6NaOH(aq) 5NaCl(aq) + NaClO3(aq) + 3H2O

Oxidation state
0 -1 +5

Six chlorine atoms oxidation state zero change to five chloride ions oxidation state -1
and chlorine in one ClO3- ion with oxidation state +5
Chlorine is simultaneously oxidised and reduced. This is called disproportionation.


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(a) Ion-electron half equations

Candidates should be able to:

write ion-electron half equations for redox reactions for which stoichiometric information
is supplied, and use titration and other data to carry out appropriate calculations;

It is sensible that candidates should be familiar with the following reductions of oxidising agents


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2S2O32 (aq) S4O62 (aq) + 2e
Hence the overall reaction between iodine and sodium thiosulfate is
I2(aq) + 2S2O32 (aq) S4O62 (aq) + 2I (aq)

The use of potassium manganate(VII) in volumetric analysis
The aqueous potassium manganate(VII) is placed in the burette and the reducing agent pipetted into

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(ii) aqueous hydrogen peroxide
H2O2(aq) O2(g) + 2H+(aq) + 2e
(Note hydrogen peroxide is reacting as a reducing agent rather than as an oxidising agent)
The overall equation is:
2MnO4 (aq) + 6H+(aq) + 5H2O2(aq) 2Mn2+(aq) + 8H2O(l) + 5O2(g)

2 mol MnO4 (aq) reacts with 5 mol H2O2(aq)…

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The use of sodium thiosulfate(VI) in volumetric analysis
Aqueous sodium thiosulfate(VI) is oxidised by aqueous iodine.
The concentration of oxidising agents can be determined by reaction with excess aqueous iodide ions,
and then titrating the iodine released with aqueous sodium thiosulfate. The aqueous sodium thiosulfate
is placed in the…

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(iii) Aqueous potassium iodate(V)
As potassium iodate(V) can be obtained in a very pure state, it can be used to standardise aqueous
sodium thiosulfate.
In the presence of excess acid, potassium iodate(V) will oxidise aqueous iodide ions.
IO3 (aq) + 5I (aq) + 6H+(aq) 3I2(aq) + 3H2O(l)

I2(aq) +…

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(ii) 10.200 g of the contents of a bottle labelled "copper(II) ethanoate, Cu(CH3COO)2.H2O", were
dissolved in water and the solution made up to 500 cm3 in a volumetric flask. 25.0 cm3 of this solution
were pipetted into a conical flask containing excess aqueous potassium iodide. The liberated iodine


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