Transcript Copper - School

What is the best method of
determining the amount of copper in a
coin and brass?
The aim of this investigation is to
investigate up to 5 different methods for
determining the amount of copper in a coin
and decide which is the best methods to
calculate the amount of copper in a brass
screw
Preparation of Copper Solutions
The concentration of your standard solution of
copper ions should match the concentration you are
likely to get from your copper coin.
What is the concentration of 3.5g of copper dissolved
in 500cm3?
Analysing copper in a coin
• To do this you must make up a large enough
reservoir of copper ions to do all your tests.
This will be about 500 cm3. If coins contain
97% copper you need to work out how much
coin is needed to make up an appropriate
concentration of copper ions
Making up the coin solution
• Copper is an unreactive metal will be
digested by concentrated nitric acid in an
oxidation reaction – This must be done in a
fume cupboard
• Cu(s) + 4HNO3(aq)  Cu(NO3)2(aq) + 2NO2(g) + H2O(l)
• You must be careful to remove excess nitric
acid with sodium carbonate followed by
ethanoic acid
Method 1 – Iodine/ thiosulfate titration
In this method the Cu2+ ions are reduced by
iodide ions to Cu+ and form a precipitate of CuI.
2Cu2+(aq) + 4I-(aq)  2 CuI(s) +
I2(aq)
The liberated iodine is then titrated against a
standard solution of sodium thiosulfate to
determine the amount of iodine and therefore
the original amount of copper ions
I2(aq) + 2S2O32-(aq)  S4O62-(s) + 2 I-(aq)
Method 2 EDTA titration
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EDTA will form a complex ion with transition
metals such as Copper to form a Cu(EDTA)2A titration with a standard concentration of
EDTA can be used to determine the
concentration of Cu2+ ions
Structure of Metal EDTA comples
3 . Gravimetric determination of copper
Theory – In this method a solid precipitate of a
copper salt is formed from copper ions. The
weight of the precipitate can be used to determine
the concentration of copper ions present in the
original solution
It is important that the precipitate produced is
very insoluble – you can show this by quoting the
solubility product – theory)
3 . Gravimetric determination of copper
The usual method of doing this is to form a precipitate of CuSCN –
Copper(1) thiocyanate
The first stage of this process is to convert Cu2+ ions into Cu+ ions as
2Cu2+(aq) +HSO3-(aq) + H2O  2Cu+(aq) + HSO4-(aq) + 2H+(aq)
You then add Ammonium thiocyanate solution as the thiocyanate
ions (SCN-(aq)) produce a precipitate of copper (I) thiocyanate
Cu+(aq) +SCN-(aq)  CuSCN(s)
Method 4. Copper Colorimetry
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Copper ions are able to absorb visible light as
this is a property of transition metals.
The amount of visible light absorbed can be
measured using a colorimeter
The amount of light
absorbed increases
as the concentration
of copper ions
increases
Calibration Curve
Make up solutions of known concentration of copper ions and
measure absorbance
Plot calibration curve
Then measure absorbance of your own sample and determine
concentration
5. Electrochemical Cell
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An electrochemical cell can be made using standard
solutions of Copper and Zinc.
The voltage of this cell should be 1.10V providing the it is
produced with 1.0 M solutions of Copper ions and Zinc ions.
As the concentration of copper varies so does the Voltage
of the cell according to the Nernst equation
Copper/Zinc Cell -
Analysing Copper in brass
• The results of this investigation can be to
select the best methods to determine the
amount of copper in brass.
• This is a more complex analysis because the
presence of zinc ions makes it more difficult
• You can analyse the amount of zinc as well as
copper in the sample
Copper Complex – Planning
• Read the articles provided to get some
background about aspirin and understand
the synthesis of it
• Read the practical methods and familiarise
yourself with the techniques
• Have a think about how complex you want
your project to be
Copper – Risk Assessment
• There are a number of chemicals need to
be carefully assessed for risks e.g.
• Conc Nitric acid
• EDTA
• Ammonia
• Ammonium thiocyannate
• Ethanol