Water Quality Testing
An experiment for CHEM 1212K.
Introduction
Water and Analytical Chemistry
The use of analytical chemistry to determine the concentrations of certain substances in water is
an important aspect of municipal and industrial water management. In wastewater treatment
plants, analysis of the water exiting the plant provides
end
―
-of-
pipe? metrics that verify the
safety of the water for human consumption. Analytical testing of environmental water can reveal
problematic contamination of natural lakes, rivers, or streams. Industrial companies that use
large amounts of water depend on measures of water quality to ensure that their products are safe
and consistent.
Whether in a natural or man-made environment, analytical water testing often relies on the
conversion of aqueous species to known forms that are easily measured, such as colored
compounds or solids. Each analytical method involves a particular chemical transformation that
is
specific
for the species of interest and
quantitative
(i.e., the species is converted completely to
a measurable form). Although these ideals can never be achieved in practice, they provide a
standard to which all quantitative analytical chemists should aspire.
In this experiment, we will study some components of municipal and natural water, neither of
which are strictly considered pollutants. It is important to appreciate that the impact of pollutants
on environmental water can be complex and indirect. In the early days of pollution control,
environmental chemists focused on concentration as the major determinant of toxicity. Pollutant
concentrations were measured directly and efforts centered on lowering the concentrations of
pollutants in municipal water to minimally toxic levels. More recently, it has become clear that
some pollutants can cause harm indirectly by decreasing the concentrations of
beneficial
dissolved species. For example, dumping of organic material into a natural water system can
cause an increase in amounts of bacteria and algae in the water. These microorganisms in turn
deplete dissolved oxygen in the water, harming fish and other aquatic wildlife that depend on the
dissolved oxygen for respiration. In this context, climate change represents an important non-
traditional pollutant, as temperature
affects the concentration
of dissolved oxygen as well.
Some minerals dissolved in water provide demonstrated health benefits. Calcium and magnesium
ions that contribute to water
hardness
are two important examples. These ions are often
introduced to environmental water sources through natural rather than industrial means; for
example, hard water containing high calcium concentrations may be found in streams or springs
passing over limestone (calcium carbonate). Hardness has an important cosmetic impact on
water quality in that dissolved calcium and magnesium affect the taste of the water itself and the
perception of other flavor compounds in beverages made from the water.
