Water Chemistry
Water is an incredibly unique molecule. There is really nothing
like in the universe and it makes life on our planet possible. 71% of the Earth is covered by water and 97% of this water is
in the oceans. Water is made up of two atoms of hydrogen and one atom
of oxygen. Because of water's electronic structure, the oxygen atom
has a slight negative charge on it and the hydrogen atoms are slightly
positive... to read more click here. To learn more about seawater composition click here.
Special Properties of water
- Water has unusual changes in state
- Water is the only natural substance that is found as a gas
(water vapor), a liquid and a solid (ice) on Earth. To learn
more about water's three states click here. This same link will also tell you:
- Water has a high heat of vaporization (meaning it takes a lot of
heat to evaporate) and a high heat capacity (meaning it can store a lot
of heat).
- Water tends to stick to itself (cohesion) and other surfaces (adhesion)
- Water is a universal solvent
- Water molecules form hydrogen bonds with each other. To see a flash demo of this click here.
- Water (liquid water) is very viscous. It is 800 times more difficult to move through than air.
- (image from: Prentice Hall)
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Water pH
One of the properties of water is that it acts as a universal solvent.
This means is dissolves most things readily. When water
dissolves things that produce an excess of hydrogen or hydronium ions
it will change its pH. pH is a measure of the acidity or alkalinity
of a solution. Aqueous solutions with a pH less than seven are
considered acidic, while those with a pH greater than seven are
considered basic (alkaline). Much of the the increase in global
carbon dioxide emissions has been absorbed by the oceans. Sea
water easily dissolves carbon dioxide gas. However it does have
an impact on sea water. (image from: Wikipedia Commons)
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Questions to Research:
- Go to: http://ga.water.usgs.gov/edu/sc3.html take
the true or false quiz (before you begin the rest of this assignment.
Record your answers as well as which answers were correct and
which were false.
- Using the link in the first paragraph. Draw a picture of a water molecule. Label the oxygen and hydrogens.
- From the same link, copy down the graph density vs temperature
graph for water. Explain why water is not most dense when it is
frozen.
- The picture of the iceberg demonstrates the fact that liquid
water is more dense than solid water (Ice floats.) Explain how this property
makes life in the arctic possible for marine organisms like polar bears or ring seals.
- Using the high heat capacity of water in your explanation, explain how oceans moderate temperature.
- Using the two links under water chemistry explain what is the
average salinity of sea water. How does the addition of salt changes
the density of water.
- Why and how does changes in salinity affect living organisms?
- Write down the following sentence, adding the words adhesion and cohesion
in the correct places. "________________ is the property of water
that allows plankton to float near the water's surface.
________________ is the property of water that allows trees to easily
draw water up to their leaves."
- Read Article 1 or Article 2 and describe potential problems that
may be caused by ocean acidification. Explain how increases in
green house gases affect ocean pH.
- In your opinion, is ocean acidification a real threat? Support your opinion with at least two facts.
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