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 500cm 3 ?

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) + 4HNO 3(aq)  Cu(NO 3 ) 2(aq) + 2NO 2(g) + H 2 O (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 Cu 2+ ions are reduced by iodide ions to Cu + and form a precipitate of CuI. 2Cu 2+ (aq) + 4I - (aq)  2 CuI (s) + I 2(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 I 2(aq) + 2S 2 O 3 2- (aq)  S 4 O 6 2- (s) + 2 I - (aq)

Method 2 EDTA titration EDTA will form a complex ion with transition metals such as Copper to form a Cu(EDTA) 2- A titration with a standard concentration of EDTA can be used to determine the concentration of Cu 2+ 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)

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 Cu 2+ ions into Cu + ions as 2Cu 2+ (aq) +HSO 3 - (aq) + H 2 O  2Cu + (aq) + HSO 4 - (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) 3. Gravimetric determination of copper

Method 4. Copper Colorimetry 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 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