Chemistry Of Natural Water Essay, Research Paper

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 is

measured by a machine and matched up to the

corresponding element with the same E as was

released. This is in turn is related to the intensity of

the light emitted and the amount of light absorbed

and based on these calculations, a concentration

value is assigned. A quick overview of how the

atomic absorption spectrophotometer works

follows. First, the water sample is sucked up.

Then the water sample is atomized into a fine

aerosol mist. This is in turn sprayed into an

extremely high intensity flame of 2300 C which is

attained by burning a precise mix of air and

acetylene. This mixture burns hot enough to

atomize everything in the solution, solvent and

solute alike. A light is emitted from a hollow

cathode lamp. The light is then absorbed by the

atoms and an absorption spectrum is obtained.

This is matched with cataloged known values to

attain a reading on concentration. Because there

are so many problems with hard water, we

decided that perhaps the water on Penn State’s

campus should be examined. My partners and I

decided to test levels of divalent ions (specifically

Mg++ and Ca++ ) in successive floors of

dormitories. We hypothesized that the upper level

dormitories would have lower concentrations of

these divalent ions because seeing as how they are

both heavy metals, they would tend to settle out of

solution. The Ca++ should settle out first seeing

how it is heavier than the Mg++, but they will both

decrease in concentration as they climb to higher

floors in the dormitories. PROCEDURE We

collected samples from around Hamilton Halls,

West halls. In order to be systematic, we collected

samples in the morning from the water fountains

near the south end of the halls. We collected water

samples from each floor in order for comparison.

The reason we collected them in the morning was

so that the Mg++ and Ca++ would be in

noticeable quantities. We then went about and

tested and analyzed via serial titrations and via

Atomic Absorption Spectrophotometry. We also

obtained a TDS sample merely for the sake of

comparison, and to ensure that were in fact

dissolved solids in our water samples (without

which this lab would become moot). For the serial

titration, we merely mixed the water sample with

EBT, and then with increasing concentrations of

EDTA. The EBT served as an indicator to tell us

when the concentrations of the EDTA and the

divalent ions in solution were equal (actually it told

us when Mg++ was taken out of solution but that

served the same purpose). This allowed us to find

the concentration of the divalent ions dissolved in

solution. Based on this, we calculated the parts

per million and the grains per gallon for each water

sample. Finally, we took an AA reading for each

sample. This gave us absorption values and

concentration values for each of the two main

metals we were observing; Ca++ and Mg++. We

then plotted a graph of Atomic Absorption

Standards. These were values given to us by the

AA operator. These values helped us to calibrate

the machine. The parts per million that we find will

be based on plugging in the reported absorption

value into the resulting curve from the graph of

these values. The resulting concentration was used

as the final value for the hardness for that

particular sample. All calculations and conclusions

were done based on these final values obtained for

the concentration of Ca++ and Mg++.