Life on our planet would be impossible without water.
Approximately three-quarters
of the earth’s surface is covered with water, nearly all of
which (98%) is non-potable
seawater. There are over fifty million billion (5 x 10 12
) tons of sodium chloride and
numerous other salts dissolved in the oceans. The chemistry of
seawater is the
chemistry of a huge solution and can be largely understood in terms
of solution
chemistry. Drawing on previously covered material, this module will
demonstrate
how concepts such as colligative properties, pH, density, and
equilibrium can be
applied to the sea.
In many respects (density, pH, and salinity) seawater is similar
to human blood,
lending credence to the idea held by most scientists that life
evolved from the oceans.
This module, while it stands alone, could be used piecemeal to add
to or replace
portions of other modules. For instance, the freezing point and
melting point
activities could be done in the Solutions module, and the
conductivity measurements
described under demonstrations could be used when teaching the
Bonding module
to illustrate ionic substances. In turn, the Solutions module
contains demonstrations
of the Tyndall effect and the relationship between temperature and
gas solubility
that are suitable for inclusion in a discussion of seawater, and the
Biogeochemical
Cycles module details the carbon dioxide water equilibrium. This
module is a natural
extension of the module on Alkali Metals, since much of the chemistry
of seawater
revolves around the metal cations Na + and K + .
This is not a fundamental or core module so there are no concepts
that absolutely
“must be covered.” Instead, the central theme of this
module is that the chemistry
of the oceans is the same as that covered in many other units, but
applied to the
complex system of the sea. The sea, in turn, is one component of the
interaction
between land, air, and sea. The questions to be asked and partially
answered are:
1. What is seawater?
2. What are the physical and chemical properties of seawater?
3. Where do the components of seawater come from?
4. What are the uses of seawater?
1. Acids/bases
2. Equilibrium, particularly LeChatelier’s principle
3. Concentration units
4. Electrolytes and the conducting of electricity
5. Solubility
6. Thermochemistry
7. Colligative properties
1. pH calculations
2. Predictions of equilibrium shifts based on changing concentrations, pH, temperature, etc.
3. Unit conversions, particularly applied to concentrations (e.g., molarity, ppm,Êg/L)
After completing this module, students should be able to:
1. Define the components of seawater.
2. Describe and measure some of the important physical and chemical properties of seawater.
3. Discuss some of the important ramifications of the environment and seawater.
4. State some of the uses of seawater.