Section 10.6: Corrosion
Research This: Corrosion and Health, page 661
A. Answers may vary. Sample answer: In older homes, lead can be found in paint used to
decorate the home, soil surrounding the home, and plumbing. Prior to the mid-1980s, most
commercial paints contained lead. Soil became contaminated by the absorption of combusted
leaded gasoline from cars. Plumbing pipes were made of metal containing lead or lead solder.
B. Answers may vary. Sample answer: Lead may enter the human body by drinking
contaminated water, by eating lead paint chips, or inhaling lead paint dust.
C. Answers may vary. Sample answer: Lead poisoning may cause persistent fatigue, irritability,
loss of appetite, stomach discomfort and/or constipation, reduced attention span, and insomnia.
Lead can also interfere in the metabolism of vitamin D and calcium. Long-term exposure can
lead to high blood pressure and peripheral vascular disease. Lead is a neurotoxicant, or brain
poison.
Children are most vulnerable to the negative effects of lead. Childhood lead poisoning can cause
brain damage and/or mental retardation, behavioural problems, anemia, liver and kidney damage,
hearing loss, hyperactivity, developmental delays, and in extreme cases, death. Children are most
vulnerable because they have a tendency to explore things using their mouths. They are more
likely to directly ingest paint chips and contaminated soil; because lead paint dust and
contaminated soil are at ground level, children can have greater exposure to lead than adults.
D. Answers may vary. Sample answer: Lead removal is sometimes impractical because of the
expense of removing and replacing the entire plumbing system of a house. Demolishing,
removing, and replacing walls decorated with lead paint may be dangerous for the construction
crew due to the amount of lead dust generated.
E. Answers may vary. Sample answer: Instead of removing the lead plumbing entirely from a
home, cold water should be used for drinking and cooking because it will contain little or less
lead than hot water. Soft metals, like lead, are somewhat soluble in hot water. Water should be
allowed to flow for 30 s before use. Rather than removing all lead, it may be less expensive to
coat the walls with a sealant to prevent lead paint from disintegrating into dust.
F. Answers may vary. Sample answer: If I were to build a home today, I would use only
environment-friendly materials--products that have been tested and are free of toxic metals such
as lead. Plumbing pipes should be made of polyvinyl chloride (PVC) because under extreme
temperatures, the plastic will not break down into solution. Galvanized metals should be used in
the house frame to prevent metal corrosion. I would use wood that was pressure treated with
non-toxic metal solutions. I would work with a builder who was knowledgeable about such
building materials and who uses them in home construction.
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Chapter 10: Electrochemical Cells 10.6-1
Section 10.6 Questions, page 662
1. (a) The standard reduction potential for tin is –0.14 V. The standard reduction potential for
zinc is –0.76. Zinc is the weaker oxidizing agent, so zinc best protects iron against corrosion
relative to tin.
(b) Iron corrodes readily in acidic solutions, while gold and silver do not, because iron is a
stronger reducing agent. Iron loses electrons more readily, compared to gold and silver, which
are strong oxidizing agents. Gold and silver retain electrons more readily.
2. Oxygen and water or another oxidizing agent must be present for iron to corrode.
3. (a) Answers may vary. Sample answer: Magnesium is used as a fire starter in the form of a
block or stick. Zinc is used in the outer metal layer of ships to prevent corrosion. Iron is used in
steel production. Gold is used in the manufacture of jewellery and electronics.
The tendency of these agents to oxidize from greatest to least is
magnesium > zinc > iron > gold
(b) Using the standard reduction potentials table for oxidizing ability:
magnesium > zinc > iron > gold
4. Many Canadians have the underside of their cars sprayed with oil before each winter to form a
moisture barrier that prevents water from corroding the metal components of the underside of the
car. It also provides another barrier between road salts and the metal of the car’s underside.
5. Galvanized steel nails are suitable for exterior use, while regular nails are not because
galvanized steel has a zinc-electroplated exterior. Outside, nails will be exposed to far more
moisture than nails used in the interior.
Zinc does not corrode as readily as the uncoated iron in regular nails.
6. (a)
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Chapter 10: Electrochemical Cells 10.6-2
(b) Answers may vary. Sample answer: The main limitations for the use of impressed current to
protect a steel structure are cost and continuity of the power supply. There is the cost of
maintaining and supplying the inert material that acts as an anode and providing the current.
There is also the problem of supplying a direct current. The current must be continuous. During a
prolonged power failure, corrosion of the steel structure could start, and could increase during
subsequent power failures.
7. Answers may vary. Sample answer: The steel nails in water and air (test tube A) and the steel
nails in salt water and air (test tube D) showed evidence of corrosion. The nails corroded because
they were exposed to both oxygen and water, conditions that cause the formation of rust (iron
oxide). The salt water caused more corrosion because the salt acts as an electrolyte and increases
the conductivity of the solution. The nails in the drying agent (test tube B) did not rust because
they were protected from moisture. The nails in the distilled water covered in oil (test tube C) did
not corrode because they were protected from oxygen gas and water vapour by the oil.
8. Answers may vary. Sample answer: Rusticles are deposits that grow from iron structures in
oceans, such as shipwrecks. They are formed by a symbiotic network of anaerobic, sulfatereducing bacteria and fungi that use the iron as a source of energy. As iron is extracted from
wrecks like the Titanic into rusticles, some of it is released into the ocean environment as “red
dust.” Rusticles are a cause for concern for scientists for many reasons. As the rusticles dissolve
in the water, they increase the acidity of the water. As the acidity of the water increases, more
metal corrodes and more hydrogen ions are produced, which increase the acidity of the water
even further. Carbon dioxide gas is increasingly soluble with sea depth, so deep waters are even
more acidic than shallow waters. The increasing acidity of the water could have harmful effects
on aquatic life. In addition to contributing to a more acid ocean environment, the bacteria that
form rusticles produce hydrogen sulfide from the sulfate ions that are plentiful in seawater. This
can also have harmful effects on aquatic life.
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Chapter 10: Electrochemical Cells 10.6-3