1.1 What is Chemistry?

23.3. Electrolysis http://www.ck12.org

One common approach to minimize the corrosion of metals is to attach a strip of a more active metal, sometimes
called a sacrificial metal, to the structure. For example, putting aluminum rings on iron or steel structures helps
prevent rusting. Since aluminum is higher than iron in the activity series, it can be used to reduce iron cations back
to neutral Fe. Eventually, the aluminum will all be converted to Al^3 +cations and must be replaced.

Lesson Summary

• Electrolysis uses an external source of electricity to drive nonspontaneous redox reactions.


• Several metals (including sodium and aluminum) are manufactured using electrolytic processes.


• Corrosion involves the deterioration of a neutral metal into an oxidized form, which exists as an ionic complex
  with oxide, sulfide, carbonate, or other anions.


• Attaching strips of neutral metals that are higher in the activity series can protect a structure from corrosion.

Lesson Review Questions

1. How does an electrolytic cell differ from a galvanic cell?


2. Explain how to produce sodium from sodium chloride.


3. Define electrometallurgy and explain some of its primary uses.


4. Why is cryolite used to dissolve aluminum oxide in the refining of aluminum?


5. Why is fluoride contamination a problem in the refining of aluminum?


6. Write the molecular equation and the half-reactions for each of the following processes:
   a. copper + carbonic acid
   b. silver + hydrogen sulfide


7. You want to build a boat with a tin bottom. You can use screws made out of either iron or copper. Which
   metal would be best for fastening the tin to the bottom of the boat?


8. In order to prevent iron storage tanks from rusting, they have magnesium attached to them. Explain why this
   process minimizes rusting of the iron.

Further Reading/Supplementary Links

• Electrolysis of molten salts: http://www.youtube.com/watch?v=l0V4MBKQXjs


• Mining and refining aluminum: http://science.howstuffworks.com/aluminum2.htm


• Chemistry of corrosion: http://www.ce.sc.edu/deptinfo/members/faculty/ray/web1/Ugrad/ECIV%20303/Corr
  osion/Set2%20Chemistry%20of%20corrosion.pdf

Points to Consider

• Oxidation-reduction calculations play important roles in other areas of chemistry.


• Cell potentials in biology are another useful application of electrochemistry.