2. Learning Objective
At the end of this unit you should be enable to:
• discuss the various properties of water that make it
unique than other liquids
• Define acidity and alkalinity
• Differentiate between alkalinity and basicity
• Calculate the alkalinity of a water body given the
required information on the concentrations of CO3
2-,
HCO3
- and pH.
• Describe the physical and chemical parameters used
to describe water quality
3. Aquatic Chemistry and Water Pollution
Aquatic Chemistry
• Properties of water
• Chemical Reactions in Water Bodies
• Dissolved gases in water
• Acid-base phenomena in water
Water Pollution
• Water Quality
• Nature and types of water pollutants
• Characterization of Waste Waters
• Water Pollution Control
• Water quality requirements
4. Properties of Water
Water is a vitally important substance in all parts of the
environment. It covers about 70% of Earth’s surface and
occurs in all spheres of the environment. It is an essential
part of all living systems. Water carries energy and matter
through various spheres of the environment. It carries plant
nutrients from soil into the bodies of plants by way of plant
roots.
The properties of water would best be understood by
considering the structure and bonding of the water molecule
6. A single water molecule we have two hydrogen atoms
bonded covalently to an oxygen atom. The three atoms are
arranged in a V-shape structure with an angle of 105°.
Because of its bent structure and the fact that the oxygen
atom attracts electrons more strongly than hydrogen atoms,
a water molecule behaves like a dipole having opposite
electrical charges at either end. The water dipole may be
attracted to either positively or negatively charged ions like
with Na+ and Cl- during the dissolution of NaCl.
8. Water has the ability to form hydrogen bonds.
Hydrogen bond is a special type of bond that can
form between the partially positively charged
hydrogen atoms in one water molecule and the
partially negatively changed oxygen atoms in
another water molecule. Hydrogen bond holds
water molecules together with strong and also help
to hold some solute molecules or ions in solutions.
10. To have a clear understanding of water pollution you should be
able to describe the chemical interactions taking place in the
large water bodies. In the following section of the module,
Chemical Reactions in Water bodies, the solubility of
atmospheric gases in open water bodies, chemical reactions
that are responsible for the acid–base characteristics of water,
complexation reactions and their equilibria, calculations of
stability constants and concentrations of species in equilibrium
are described. Water pollution and the physical and chemical
parameters used to describe pollution, the sources of water
pollution and water pollution control are also discussed in brief.
11. Chemical Reactions in Water
bodies
Chemical interactions in natural water
system are very complex and many
variables should be taken into account
to describe their chemistry.
