CH142Exp8Electroplating.pdf - Faraday\u2019s Law 1 Experiment 8 Copper Electroplating and Faraday\u2019s Law1 Purpose An electrochemical cell is constructed

CH142Exp8Electroplating.pdf - Faraday’s Law 1 Experiment...

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Faraday’s Law 1 Experiment 8: Copper Electroplating and Faraday’s Law 1 Purpose: An electrochemical cell is constructed to determine the efficiency of copper electroplating. Chemical treatments are tested to produce a light green patina that is characteristic of aged copper. Introduction Copper roofing is a prominent part of campus architecture. While durable, copper roofing is very expensive. College architects have attempted to find cost effective alternative roofing materials. Aluminum or especially polymer coated steel roofing is significantly cheaper than copper. The characteristic color of aged copper is light green. The light green “patina” on oxidized copper is primarily a mixture of copper sulfates and oxides. Aluminum and steel roofing is commercially available with a painted green patina. However, previous college presidents have rejected the cheaper materials because the painted coatings do not resemble the aged patina on existing roofs. To make matters worse, newly installed copper roofing rapidly oxidizes to a dull dark brown, which also does not match the patina of aged copper. The dark brown patina on recently installed copper is primarily mixed copper sulfide and oxides. The color of copper oxides depends on the details of the crystal structure of the oxide, which is determined by the history of exposure of the metal to the atmosphere. The chemistry department has been asked for advice concerning treatments that produce a light green patina on copper or other roofing metals, particularly steel. The current college policy is to replace existing copper roofs with new copper and simply wait the dozen or so years that is required to produce the characteristic light green patina. In this lab exercise we consider the possibility of using a cheaper metal that has been electroplated with a thin layer of metallic copper that is subsequently treated to produce a light green patina. Electroplating is an energy intensive process. The scientific goal of this experiment is to determine the efficiency of copper electroplating on nickel coated steel or brass. The esthetic goal is to determine the suitability of several different commonly used coloring processes. These processes produce a thin layer of mixed copper salts that precipitate on the surface of the copper metal from aqueous solution. Electrochemistry: Oxidation/reduction reactions are often studied by running the reactions as electrochemical cells. For example the reaction, Zn (s) + Cu 2+ (aq) Zn 2+ (aq) + Cu (s), can be separated into two half-reactions that form the basis of the electrodes in an electrochemical cell. The electrodes in an electrochemical cell are called the cathode and anode : cathode: Cu 2+ (aq) + 2 e Cu ( s) reduction anode: Zn (s) Zn 2+ (aq) + 2 e oxidation cell reaction: Zn (s) + Cu 2+ (aq) Zn 2+ (aq) + Cu (s) The reduction occurs at the cathode. The oxidation occurs at the anode. The anode is always drawn on the left and the cathode is drawn on the right in cell diagrams, Figure 1. The cathode is the source of electrons for the reduction. The anode is the sink of electrons for the oxidation. The
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