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Electroplating

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Brass astrolabe that was gold-plated

Does anybody know where we are?

The astrolabe (pictured above disassembled) was a device used to study the motions of planets and to do surveying. Most astrolabes were made of brass, but this one has been overlaid with gold which is wearing off. Persian mystics also used astrolabes for following the stars and making astrological predictions.

Electroplating

Many decorative objects like jewelry are manufactured with the aid of an electrolytic process. Electroplating is a process in which a metal ion is reduced in an electrolytic cell and the solid metal is deposited onto a surface. The Figure below shows a cell in which copper metal is to be plated onto a second metal.

Illustration of the electroplating of copper

Electroplating of second metal by copper.

The cell consists of a solution of copper sulfate and a strip of copper which acts as the anode. The metal (Me) is the cathode. The anode is connected to the positive electrode of a battery, while the metal is connected to the negative electrode.

When the circuit is closed, copper metal from the anode is oxidized, allowing copper ions to enter the solution.

\text{anode}: \ \text{Cu}^0 (s) \rightarrow \text{Cu}^{2+}(aq) + 2e^-

Meanwhile copper ions from the solution are reduced to copper metal on the surface of the cathode (the second metal):

\text{cathode}: \ \text{Cu}^{2+}(aq) + 2e^- \rightarrow \text{Cu}^0(s)

The concentration of copper ions in the solution is effectively constant. This is because the electroplating process transfers metal from the anode to the cathode of the cell. Other metals commonly plated onto objects include chromium, gold, silver, and platinum.

Summary

  • The process of electroplating is described.

Practice

Questions

Watch the video at the link below and answer the following questions:

http://www.youtube.com/watch?v=Q8Xo43sfLgY

  1. What is the solution used?
  2. How did he test the system?
  3. Why are batteries better than wall current for the electrical current?
  4. What was the anode?

Review

Questions

  1. In an electroplating process using copper, what is the anode?
  2. What supplies the electric current?
  3. What other metals can be coated onto objects?

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