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Hardness Of Water Essay, Research Paper
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.
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.
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 CaCO3×1000 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.
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:
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.
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.
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.
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.
5. Hardness and Water Quality. http://fluid.state.ky.us/ww/ramp/rmhard.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.
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