The simulated ore in step 1 is copper. In step 1, after adding ethylenediamine,

Question

The simulated ore in step 1 is copper. In step 1, after adding ethylenediamine, the solution turns into purple colour.

I) In step 3 of procedure, what do you think the residue consists predominantly of?

Detailed procedure 1. Weigh about 5 g of the "simulated" ore into a 100 mL conical flask, then add about 20 mL of a 5% aqueous solution of ethylenediamine. 2. In the fume hood, with continuous swirling, add successive portions of about 0.5 mL of 3% (10 volume) hydrogen peroxide solution. Allow bubbling to subside between additions. The bubbling is due to evolution of oxygen produced by decomposition of hydrogen peroxide Care should be exercised when handling the ethylenediamine solution and hydrogen peroxide solution. Effervescence may be observed due to evolution of oxygen gas produced by the decomposition of hydrogen peroxide. If this occurs too vigorously, the bubbles of gas may cause splashing of unreacted hamful ethylenediamine. Continue to add the small portions of the hydrogen peroxide solution until a total of 20 mL is added. Swirl for another 5 minutes, then allow the mixture to settle 3. . Decant the slurry into a clean beaker and wash the residue several times with a small volume of water. Add these ensure that all the copper-complex is collected. Add a pea-sized sample of powdered zinc and stir the solution until all the copper has been displaced. If the displacement is not complete after a short while, more zinc may be added Do NOT add too much zinc powder as rinsings into the clean beaker to 5. this may make the recovery of the pure copper more difficult. 6. Decant the solution. Wash the residue with deionised water and decant the liquid at least twice. 7. The black residue is a mixture of copper metal and surplus (unreacted) zinc. In the fumehood, remove the zinc by adding about 4 mL of 3 M sulfuric acid solution. Take care as this is a vigorous and exothermic reaction. 8. The residue should now be pure copper. Decant the solution from the residue and wash the residue (decanting the wash liquid) at least twice with deionised water 9. Dry the residue (your demonstrator will guide you through this step) and record the mass of your recovered product.

Explanation / Answer

1)Copper and ethylenediamine give a copper ethylenediamine complex which on reaction with hydrogen peroxide gives a superoxide of copper ethylenediamine.The residue is thus the superoxide of copper ethylenediamine.

2)The superoxide then reacts with zinc and pure copper is obtained.The residue contains a complex of zinc, pure copper and unreacted zinc.

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