Anode and cathode in the electrolysis ofCopper sheet with nickel
Answers
Answer:Experiment 8: Copper Electroplating and Faraday’s Law1
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) + Cu2+ (aq) → Zn2+ (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: Cu2+ (aq) + 2 e– → Cu (s) reduction
anode: Zn (s) → Zn2+ (aq) + 2 e–
oxidation
cell reaction: Zn(s) + Cu2+ (aq) → Zn2+ (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
solution in contact with the electrode is called the electrolyte of each half-reaction or half-cell.
The electrolytes conduct electrical current within the electrochemical cell. Wires attached to the
electrodes conduct the electrons between the cathode and anode through a voltmeter or current
source. An electrochemical cell that is spontaneous is called a galvanic cell. Batteries are
examples of galvanic cells. Galvanic cells are sources of energy, for example for running cell
phones. The cell voltage of a galvanic is measured with a voltmeter. A non-spontaneous
Explanation: