FREE ESSAY ON HARDNESS OF WATER

HARDNESS OF WATER

Water is the most important molecule that exists on the Earth. Without water living beings
would not be able to live. Water is used for an immeasurable number of things. There are
many properties of water, which makes this molecule so unique. One which people overlook
is hardness. Hardness is defined in the Chemistry: The Central Science by Prentice Hall's
as being "water that contains a relatively high concentration of Ca2+, Mg2+, and other
divalent cations." Water containing these ions is not a health hazard; however, it is a
problem for industries and households. Therefore, the hardness of water is vital to
understand in order to prevent the problems it could cause.
For one to have a better understanding of hardness, you must know how water becomes hard
or what causes water to become hard. All water that we use is freshwater which is
transported through many pipes. The ions Ca2+ and Mg2+ react with water and form
insoluble substances which causes blockage and deposits to form. Some examples of how
this affects industries and households are the insoluble substances that form and cause
soap scum, scaling in water heaters in factories, and clogging of pipes which transports
water places. There are many techniques in which water undergoes in order to decrease the
amount of ions in the water before the water comes to your faucet. Although people can
take most ions out of the water, not all ions can be removed. The following chart shows
the classifications of water and their hardness. In this chart, 1 ppm hardness is equal
to 1 part of CaCO3 per million parts water, which is also equal to 1 mg CaCO3 in 1 liter
of water.
Table A 
Concentration mg/L CaCO3 Description 
0 - 75 soft 
75 - 150 moderately hard 
150 - 300 hard 
300 and up very hard
This data is used as a guideline for people to determine how hard/soft the water is.
An experimental procedure in Penn State's version of Chemtrek August 2000-July 2001 on
pages 10-12 to 10-20, which was written by Stephen Thompson, is a good procedure to
determine the hardness of water. They used two different types of testing in order to
compare the different results, the EBT and atomic absorption analysis and EDTA titration.
The first procedure we did was the atomic absorption (AA) analysis. This was done by
using a AA spectroscopy. First the water sample was by atomized and then a beam of
monochromatic light is fired from a hollow cathrode lamp which emits a light that is set
at a certain frequency that has the same frequency energy as the element you are trying
to evaluate. The amount of light of the special frequency absorbed by the atomized sample
reflects the quantity of the element that is set for. The calibration of the AA
Spectroscope is found by putting samples with known concentrations into it and making a
graph of the absorptions recorded from them and then by finding a corresponding
regression line. The two following graphs A and B are the graphs with the plots that our
instructor, Bin Gu, gave to us in class. 
Graph A
Graph B
Therefore, values for samples with unknown concentrations can be derived from the
calibration graphs by plugging in the concentration into the equation. For example, with
the water sample from Panama City, FL, the Mg concentration found using the AA test was
29.04 mg/L. If we plug that number in then we get the number .5724 which we can compare
to the absorbance level which was .5773. It seems that the equation is pretty accurate.
Next, we conducted a Total Dissolved Solids (TDS) testing. This was done by evaporating
two drops of water, our sample water and distilled water. We then compared how much
residue was left over concluding that there is more ions that are insoluble in the same
water than distilled water. 
The next part of the experiment was to do the EDTA titration test. This test involved
adding agents to the water sample and then titrating that solution with EDTA. The first
time we did a titration with a known concentration of Ca ions. The next time we did the
titrations we used our water sample which gave us the calculation of the concentration of
the Ca ions in our sample. This is what we used to compare the hardness of our
sample.This titration test procedure consisted of adding a drop of EBT indicator and a
drop of NH3/NH4Cl/MgEDTA buffer to a drop of the water sample. The hard water sample is
then titrated with the EDTA. This experiment determines the hardness by first forming a
basic solution with the buffer and having the indicator show this. Then, when the EDTA is
added, it first reacts with the Ca and forms a colorless chelate, and then the Mg reacts
with it forming another colorless chelate. After all of the Mg has reacted with the EDTA,
the titration is complete and the indicator shows the solution as a clear blue. The
amount of ions in the solution can be determined by setting up a ratio between the drops
(volumes) of EDTA and the ions and equating it to the ratio of the concentrations of the
two. This is the formula you should use in order to find the unknown titration:
CEDTA VEDTA = CIONS VIONS
-Example of calculation 1 -(2.00 x 10-4 M) x 14 drops = CIONS x 1 drop CIONS = .0028 M
Since the concentration of the ions is known in Molars, it can be converted to parts
CaCO3 per million, the standard hardness unit. The following example is a guidline of how
to convert the units. 
Example of calculation 2-
3.2 x10-3 mol CaCO3 x100 g CaCO3x1000 mg CaCO3=320 mg =320 mg=320 ppm
liter mol CaCO3 1 g CaCO3 L 1000 g
The last part of the experiment was to do a EDTA titration with our water sample and an
added comerical agent water softener. This part of the procedure was to show the effect
that water softeners have on the ions in the water. The first softener used was baking
soda and the second softener was done by resin beads which reacted with the water by ion
exchange, which removed the Ca and Mg ions. This concluded the lab and with all this
information, we compared and made conclusions about our water samples. 
This experimental procedure was completed in order to find the hardness of samples of
water. My group has chosen three different types of tap water from three different areas
in order to show the comparison of the hardness of tap water. The samples were taken from
East Halls (Hastings) in State College, a house in Pittsburgh, PA (2418 Rolling Farm's
Road), and from a hotel room in Panama City, FL. We assumed for our hypothesis that the
water from East Halls would have been the hardest due to the size and the length of
travel of the water through the large pipes, which are underground. 
Through testing the water samples by AA and EDTA testing, we concluded that the water
from Florida was the hardest. Next came the sample from East Halls, State College, and
then the sample from Pittsburgh, PA. The following table is a summary of both tests, the
AA and EDTA titration testing.
Table 2
Source of Water Concentration of Ca from AA Test Absorbance Value for Ca from AA Test (at
422.7 nm) Concentration of Mg from AA Test Absorbance Value for Mg from AA Test (at 202.5
nm) Concentration of Ca from EDTA Titration
Tap in Dorm Room in East Halls 25.55 mg/L 0.429 18.75 mg/L 0.3771 140 ppm
Tap from House in Pittsburgh, PA 20.29 mg/L 0.3424 6.02 mg/L 0.154 120 ppm
Tap from Hotel Room in Panama City, FL 29.1 mg/L 0.4888 29.04 mg/L 0.5773 320 ppm
We have proven that our hypothesis was wrong. This hypothesis is wrong because of the
error of research. We thought since the system in the dorms would be the hardest because
of the large pipes underground which would have a greater change of letting ions enter
the water. However, the water from the hotel room was the hardest because for one reason
it was taken from a completely different state in the United States and therefore shows
that different areas have different ways to contribute tap water to citizens. The sources
of the water may differ depending on what location or what the surrounding geography is
like around the city (ex: ocean, river, large city). 
The results for the TDS testing proved that our water sample did contain ions which left
a residue. By comparing it to the distilled water drop, you could plainly see that the
distilled water had much less residue or ions. Next, our outcomes were slightly different
between the two different tests for our water samples. For example, in Table 2 the first
test on the dorm water seems to be pretty accurate (140 ppm EDTA and 140.9 ppm AA);
however, the other two samples vary between each test (120ppm EDTA and 75.4 ppm AA for
the second sample and 320 ppm EDTA and 192.5 ppm AA for the third sample). This occurred
because of human error. The EDTA testing is not as accurate as the AA testing because the
EDTA testing is completely done by human calculation and observation. During the
titration process, there could have been contamination in the wells and/or the pipets,
which we were using in the experiment. Also, the observations could have been affected by
this contamination. If the color changed too quickly/slowly, some of the chemical that
causes the color change could have been present/absent in value compared to what was to
be present/absent in value. However, even though the tests had different quantitative
values, the overall picture is accurate. They still fit into the categories in Table 1,
how hard/soft they are depending on how much ions are present in the water samples. Both
the two tap water samples from State College and Pittsburgh, PA were soft and the hotel
room water from Florida was hard as you can see in the following table:
Table 3
Source of Water Total hardness from AA test. Total hardness from EDTA test.
Tap in a dorm (East Halls) 140.9 ppm 140 ppm
Tap from House in Pittsburgh, PA 75.4 ppm 120 ppm
Tap from hotel room in Panama City, FL 192.5 ppm 320 ppm
The last result for the experiment was the water softening agents. The results of the
softening tests showed that the ion exchange resin reduce water hardness more than the
baking soda. The following table shows the difference. 
Table 4
Source of Water pH of Water pH of Water with Resin Beads
Tap in Dorm Room in East Halls 8 5
Tap from House in Pittsburgh, PA 7 3
Tap from Hotel Room in Panama City, FL 8 4
This table shows that with the resin beads the water became more acidic. The ion exchange
resin works to soften by exchanging 'soft' ions for 'hard' ions. After both procedures
with the water softening were completed, we did a EDTA titration test one the samples.
Through the equation I used earlier (example equation 1), we found that the data proved
the softener worked. By using the second equation (example equation 2) I found the total
hardness of the water with the softener and I reported the data in Table 5 below. As you
can see the baking soda did exactly what it was thought to do, it softened the sample
water. 
Table 5
Source of Water Total hardness from EDTA test with softener. Total hardness from EDTA
test without softener.
Tap in a dorm (East Halls) 80 ppm 140 ppm
Tap from House in Pittsburgh, PA 60 ppm 120 ppm
Tap from hotel room in Panama City, FL 280 ppm 320 ppm
The Baking soda agent was more effective than the resin beads. 
In conclusion, our hypothesis was proven false by the experiment. The reason for the fact
that the tap waters pick up many impurities in their travels from being rainwater to
coming out of the faucets. However, State College's water purification system has been
lately improved which is why the water here in State College is lower than the tap water
in FL. Also, due to the fact that both the water from State College and Pittsburgh, PA
comes from a near by water purifying company. Since there is so many residence in the
areas of where the tap water was taken, the demand for water is more than in Panama City,
FL where not as many residents live there . FL water purifying company is not as close to
the hotels and therefore, the water will collect more ions as it has a farther distance
to travel than the waters from the dorm and the house. This is the reason that the tests
in the lab gave data to support this new hypothesis: water from the tap in a residential
area is less hard then areas farther away from the water purifying company.
References 
1. Brown, Theodore L., H. Eugene LeMay Jr., Bruce E. Bursten. Chemistry: The Central
Science. Upper Saddle River: Prentice Hall, 2000.
2. Thompson, Stephen. PSU Version of Chemtrek: August 2000 to July 2001. Englewood
Cliffs: Prentice Hall, 2000.
3. http://courses.chem.psu.edu/chem14/water.pdf.
4. http://www.cciw.ca/gems/atlas-gwq/gems12.htm.
5. Hardness and Water Quality. http://fluid.state.ky.us/ww/ramp/rmhard.htm.
6. http://www.cciw.ca/gems/atlas-gwq/gems10.htm.
Additional credit is given...for their contributions from the dorm tap water, and the
house tap water. Also, for their data given from the same lab procedure.