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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WJEC
CBAC
AS/A LEVEL
GCE in Chemistry
REVISION AID
CH5

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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 Chemistry of the p ­ block
16.2 Group 3 (13)
16.3 Group 4 (14)
16.4 Group 7 (17)
TOPIC 17 - d-block transition elements
TOPIC 18 - Chemical kinetics
TOPIC 19 - Energy changes
19.…read more

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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 as electron loss and reduction as electron gain.
The following equations represent examples of redox reactions and the half equations clearly show the
transfer of electrons.…read more

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Cl2(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.…read more

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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
MnO4 (aq) + 8H+(aq) + 5e Mn2+(aq) + 4H2O(l)
Colour change purple to almost colourless
Cr2O72 (aq) + 14H+(aq) + 6e 2Cr3+(aq) + 7H2O(l)
Colour change orange to green
I2(aq) + 2e 2I (aq)
Colour change brown to…read more

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S2O32 (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
the conical flask with an excess of aqueous sulfuric acid. These titrations require no external indicator.…read more

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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)
The use of potassium dichromate(VI) in volumetric analysis
Here the orange aqueous potassium dichromate(VI) is placed in the burette but this time an indicator is
required e.g. during the oxidation of aqueous iron(II) ions.…read more

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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 burette; the oxidising agent is pipetted into the conical flask which contains excess
aqueous potassium iodide.…read more

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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) + 2S2O32 (aq) S4O62 (aq) + 2I (aq)
1 mol IO3 (aq) requires 6 mol S2O32 (aq)
The specification requires, "use titration and other data to carry out appropriate calculations".
Examples of worked calculations
(i) 25.…read more

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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
was titrated against aqueous sodium thiosulfate of concentration 0.1000 mol dm 3, using starch as
indicator near the end-point.
The volume of aqueous sodium thiosulfate required was 24.95 cm3.
Calculate the percentage purity of the copper(II) ethanoate.…read more

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