Experiment 2: The Copper Mirror

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Background
Copper is widely distributed in Nature as metal, in sulfides, arsenides, chlorides, carbonates, etc. Copper is also the third most abundant metallic element in the human body, following iron and zinc, and it is important in all other life forms. Copper-containing biomolecules like azurin and plastocyanin found in algae and green leaves, participate in electron transfer reactions. Hemocyanin, found in molluscs, is functions as an oxygen carrier. Cytochrome c oxidase, found in mitochondria, participates in the interconversion between water and oxygen. The
biochemistry of copper relies primarily in its oxidation-reduction chemistry. \(Cu^{2+}\) in solution can be reduced to metallic copper by the addition of a strong reducing agent, such as hydrazine (\(N_2H_4\)). The oxidation products of hydrazine are strongly dependent on the pH of the solution, the temperature, the oxidizing agent used, and the catalytic impurities present.

Materials:

One large test tube
5 mL of 1M copper sulfate (\(CuSO_4\)) solution
1 mL of 85% hydrazine hydrate solution

SAFETY

Hydrazine hydrate solutions are toxic, a suspected carcinogen, highly reactive and highly flammable. Symptoms of exposure include burning sensation, coughing, shortness of breath, headache, nausea. Carry out the experiment in a well-ventilated hood.

Procedure

Rinse the test tube with distilled water, nitric acid, distilled water, acetone, and distilled water in that order.
Add 5 mL of copper solution to the test tube, followed by 1 mL of hydrazine hydrate solution. Swirl once. The blue solution will immediately turn to a brownish-green.
Immediately place the test tube in a hot water bath.
Swirl the tube lightly and record your observations.
To remove copper from the test tube walls use 1 mL (20 drops) concentrated nitric acid. Record your observations. Add 3 mL of water. Record your observations.

Clean-Up: The chemical waste should be disposed in the designated containers.
Discussion: Write the balanced chemical equations for all processes.