The Chemistry Of Natural Water


The purpose of this experiment is to explore the hardness of the water on campus. Hard water has been a
problem for hundreds of years. One of the earliest references to the hardness or softness of water is in
Hippocrates discourse on water quality in Fifth century B.C. Hard water causes many problems in both in
the household and in the industrial world. One of the largest problems with hard water is that it tends to
leave a residue when it evaporates. Aside from being aesthetically unpleasing to look at, the build up of
hard water residue can result in the clogging of valves, drains and piping. This build up is merely the
accumulation of the minerals dissolved in natural water and is commonly called scale.

Other than clogging plumbing, the build up of scale poses a large problem in the industrial world. Many
things that are heated are often cooled by water running thru piping. The build up of scale in these pipes
can greatly reduce the amount of heat the cooling unit can draw away from the source it is trying to heat.
This poses a potentially dangerous situation. The build up of excess heat can do a lot of damage; boilers
can explode, containers can melt etc. On the flip side of the coin, a build up of scale on an object being
heated, a kettle for example, can greatly reduce the heat efficiency of the kettle. Because of this, it takes
much more energy to heat the kettle to the necessary temperature. In the industrial world, this could
amount to large sums of money being thrown into wasted heat.

In addition to clogging plumbing and reducing heating efficiency, the build up of hard water also
adversely affects the efficiency of many soaps and cleansers. The reason for this is because hard water
contains many divalent or sometimes even polyvalent ions. These ions react with the soap and although
they do not form precipitates, they prevent the soap from doing it\'s job. When the polyvalent ions react
with the soap, they form an insoluble soap scum. This is once again quite unpleasing to look at and stains
many surfaces.

The sole reason for all these problems arising from hard water is because hard water tends to have higher
than normal concentrations of these minerals, and hence it leaves a considerable amount more residue
than normal water. The concentration of these minerals is what is known as the water\'s Total Dissolved
Solids or TDS for short. This is merely a way of expressing how many particles are dissolved in water.
The TDS vary from waters of different sources, however they are present in at least some quantity in all
water, unless it has been passed through a special distillation filter. The relative TDS is easily measured
by placing two drops of water, one distilled and one experimental on a hotplate and evaporating the two
drops. You will notice that the experimental drop will leave a white residue. This can be compared to
samples from other sources, and can be used as a crude way of measuring the relative TDS of water from a
specific area. The more residue that is left behind, the more dissolved solids were present in that
particular sample of water. The residue that is left, is in fact, the solids that were in the water.

Another, perhaps more quantitative way of determining hardness of water is by calculating the actual
concentrations of divalent ions held in solution. This can be done one of two ways. One is by serially
titrating the water with increasing concentrations of indicator for Mg++ and Ca++ (we will be using
EDTA). This will tell us the approximate concentration of all divalent ions. This method of serial
titrations is accurate to within 10 parts per million (ppm) .

Another possible method for determining the hardness of water is by using Atomic Absorption
Spectrophotometry or AA for short. AA is a method of determining the concentrations of individual
metallic ions dissolved in the water. This is accomplished by sending small amounts of energy thru the
water sample. This causes the electrons to assume excited states. When the electrons drop back to their
ground states, they release a photon of energy. This photon