Science 24 Tutorial – September 30th, 2003
Overview of what is due this week. U1 test is on Oct. 8th.
Begin with information from the last lesson on global warming.
One of the concerns that we have identified that are associated with the burning of fossil
fuels is global climate change resulting from the greenhouse effect.
Many other chemicals get released into the air that are considered to be pollutants and
can be harmful to living things.
What are the sources of some of these pollutants?
Ans. Refer to pages 64 and 65 in text.
(volcanoes, forest fires, cars, industrial smokestacks.
What is acid deposition?
Ans. The result of air pollutants combining with each other to produce acid precipitation
or rainwater that has become more acidic.
Refer to the pH scale at the top of page 67. The pH scale measures acidity.
Acid = pH lower than 7
Base = pH higher than 7
Neutral = pH of 7
Where does acid deposition fall on the pH scale?
Ans. pH of less than 5.6
How can acid deposition cause harm to the environment?
Ans. Kills vegetation, kills living things in a lake.
Lakes can be temporarily restored to an acceptable pH level to support life, but why
would liming not be a permanent solution to the effects of acid precipitation.
Ans. –Expensive…has to be done regularly. Liming does not solve the problems of
changes in soil chemistry, forest health, risk to human health etc.
Acid deposition penetrates deeply into the fabric of an ecosystem, changing the chemistry
of the soil as well as the chemistry of the streams and narrowing the space where certain
plants and animals can survive. It can take decades or centuries for the area to heal.
What other steps must be taken?
Ans. Prevent the acid deposition by:
- removing the sulphur from the fuel before the fuel is burned.
- Sulphur scrubbers installed in smokestacks (talk through the picture on page 68.)
What steps can you take to conserve energy and reduce emissions that can lead to acid
deposition.
Ans.
-turn off lights, computers etc when not in use.
-use energy efficient appliances
-Don’t keep your thermostat too high.
-insulate your home
-carpool, cycle
In lesson 11 (which is due on Thursday), you will revisit the neutralization reaction.
What is the general equation for a neutralization reaction?
Ans. Acid + base - salt and water.
Acids are formed when molecules containing extra hydrogen ions (H+) are dissolved in
water. Bases are formed when molecules containing extra hydroxide ions (OH-) are
dissolved in water. The two combine to form HOH or H2O. What is this compound?
Ans. Water.
One of the last topics that you will learn about in this unit is corrosion.
What is corrosion?
Ans. Any process that chemically breaks down or degrades metal eg. rusting. The rust
flakes off and exposes more metal which in turn rusts. This weakens structures such as
bridges. Corrosion is one type of oxidation-reduction. A metal will corrode whenever it
is exposed to a substance that will take electrons from it – oxidize it. Oxidation occurs
when a metal reacts chemically with oxygen in the presence of water to produce a new
material. The new material is called an oxide.
How is rusting prevented?
1. painting – a protective coat which prevents oxygen and water from reaching the
surface of the metal. However, paint can chip and then rusting occurs.
2. galvanizing – process of applying a zinc coating to iron or steel. To do this the
metal is immersed in a bath of molten zinc which leaves a barrier between the
metal and the environment.
3. sacrificial metal – a second metal attached to the one that you don’t want to rust.
Eg. magnesium bars attached to a pipe. The magnesium will corrode but the
pipeline will not. The magnesium would be the sacrificial metal.
*Import power pt slide on relative tendency to corrode.
Explain that this table helps you predict corrosion of metals in contact. For
example, zinc is coated on iron in galvanizing to protect iron from corroding. Any
metal above iron in the table would tend to protect iron because it would corrode first.