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Ben Torres 11/13/12Chem 111 Section103 Mike ShadeckExperiment 10The Chemistry of Natural WatersBen TorresAlicia WhiteRobert WertzMatt WertmanINTRODUCTIONWater hardness is a term often used to define how many ions can be found in a sample of water being tested1. The ions most often looked at are Calcium and Magnesium. The higher the concentration of the Ca2+ and Mg2+ ions in the water the higher the hardness is1. On the contrary, if water has a low concentration of these two ions it is labeled “soft”. The units to measure the hardness of water are as follows: molarity (M), parts per million (ppm), mg/L (which is equal to ppm), and grains per gallon. Ranges for determining if water is hard or soft have been established and are3:Mg/LClassificationLess than 17.1Soft17.1-60Slightly Hard60-120Moderately Hard120-180HardAbove 180Very HardThe quantity of these ions in the water is important in its use as both drinking water and industrial water. It’s important to study water hardness for many reasons but one major one is that studies show that higher levels of these two ions have been shown to reduce the chance of having diseases like cardiovascular and cerebrovascular1. The two major techniques used for determining the hardness of water are EDTA titration and Atomic Absorption Spectrophotometry2. EDTA titration analysis uses EBT indicator (eriochrome black) and the water samples together. When added together magnesium reacts with the EBT and forms a wine red color2. Next the EDTA solution is added in an increasing interval to the mixed solutions of the water sample and EBT indicator. The combination of EDTA, EBT, and magnesium ions react all together and turn the solution blue2. EDTA is successful when magnesium ions are present in the water sample and are chelated when EBT is added.The second process used is Atomic Absorption Spectrophotometry (AA). The basis for AA is the Beer-Lambert law. The Beer-Lambert law relates the absorption of light to the properties of the material through which the light is travelling. AA spectrophotometers shine a monochromatic light through a given atom and measure the amount of ions present in the water in this case. The AA spectrophotometer converts the water into an aerosol by heating it up via flame2. Then the spectrophotometer shoots a light through the flame where the sample is then atomized. The light will only be absorbed if there is a matching energy separation of electronic energy levels2. This energy separation or wavelength is specific to either calcium or magnesium. Then a computer in the AA spectrophotometer calculates the absorbance values of the Ca2+ and Mg2+ ions in the water.These two techniques are different but both useful. EDTA can analyze the water and all the cations present. EDTA is flawed in the fact that it cannot measure the separate the amounts of the ions. Thankfully AA spectrophotometry can accurately calculate the absorbance values of both the calcium and magnesium ions present. Due to the need to soften water different processes have arose. Some examples of these softening techniques are the addition of lime and soda, which precipitates the magnesium and calcium4,5. Other techniques are ion exchange, which is when sodium ions replace the ions in the water4. The water passes through a chamber containing resin beads and the sodium ions switch places with the calcium and magnesium4.For our experiment my group tested water from four different places on and off the Pennsylvania State University campus. My sample came from a water fountain in the Simmons residence hall. Alicia’s sample came from her off campus apartment sink7. Bobby’s sample came from the showers in the East residence halls9. Matt’s sample came from a puddle next to a sidewalk on the campus8. My hypothesis will be that Matt’s water will be the hardest. I believe this to be true because the water will have absorbed calcium and magnesium from the earth and thus it will have higher amounts of both these ions. I expect the second hardest to be Alicia’s water because her sink overtime can develop calcium and magnesium buildups on it and they make the water passing through it harder. Finally expect my sample to be the next hardest closely followed by Bobby’s. My water is drinking water and is made intentionally hard to eliminate some contaminants in it. Bobby’s showerhead water is not drinking water but I expect that it comes from a similar, if not the same, source as mine. PROCEDUREEach member of the group preformed their own experiments on their own water samples. The procedure for this experiment came from PSU version of Chemtrek2. All group members preformed the same steps.We started by testing our water samples using the AA spectrophotometer. We filled up two pipets with our water samples that we had diluted with a 1:1 ratio of distilled water to our water sample. We then brought our samples to the machines where we placed a tube into our samples, which turned the water into an aerosol. Then flame heats up the aerosol. This process was preformed twice because there was a machine that calculated the absorbance valuesFirst, a 1inch x 1inch aluminum foil square was cut out and one drop of distilled water, undistilled sample water, and 1x10-3 M Ca2+ were all dropped on the aluminum foil2. Then the residue of the total dissolved solids was observed and recorded. Then EDTA titration was preformed on the water samples. The water samples were organized in a 12-well strip provided. One drop of the water samples was placed in each well of the 12-well strip. Then a drop of the EBT indicator and one drop of NH3/NH4Cl/MgEDTA buffer was added in each well. Next serial titration was preformed with 2x10-4 EDTA. Once all the Ca2+ and Mg2+ reacted with the EDTA the wells went from the color pink the color blue2. The well used to find the total ion concentration was the well before the first blue well2.The final steps of our experiment were to attempt to make our water softer using two techniques. The first technique we used was water softening with a commercial water-conditioning agent. Our water sample was mixed with 20mg of the softening agent. The pH of the water was recorded before and after this occurred. The second softening technique used was divalent cation removal by ion exchange. This time we took our water samples and mixed them with some cation exchange resin. We shook the vial and mixed the two let them sit then removed the supernatant liquid using a pipet. Once again the pH of the water was tested before and after the process.RESULTSTABLE 1. Observations Of TDS residue after water evaporation from one-drop samplesSampleObservationA. Distilled WaterNo residueB. 1x10-3 M CaCl2 ReferenceFaint ringC. Simmons Water Fountain6Heavier White residue ring compared to referenceD. Apartment Sink7Similar to referenceE. Puddle8Heavier ring compared to referenceF. Shower9Similar to referenceTable 2: EDTA results from water samplesConcentration (M)Concentration (ppm)Grains per GallonSimmons Water fountain62.8x10-3 M280 ppm16.37Apartment Sink72.0x10-3 M200 ppm11.69Puddle84.0x10-3 M400 ppm23.4Shower93.2x10-3 M320 ppm18.7Equation1: Calculation of molarityMEDTA×VEDTA=MSAMPLE×VSAMPLECalculations with my numbers(2.0x10-4)(7 Drops)=MSAMPLE(1 Drop)MSAMPLE = 1.4x10-3 MThen multiply times two because of dilution ratio2.8x10-3 MEquation 2: Calculation of parts per million (ppm) = mg CaCO3/L of solutionMoles Divalent Cations X 100.0 g CaCO3 X 1000 mg CaCO3 = mg CaCO31 Liter of Solution 1 Mole CaCO3 1 g CaCO3 1 Liter of SolutionSimmons Water Fountain61.4x10-3 M X 100.0 g CaCO3 X 1000mg CaCO3 = 140 mg CaCO31 Liter of Solution 1 Mole CaCO3 1 g CaCO3 1 Liter of Solution140ppm* Equation 3: Calculations of Grains per GallonPpm of sample X 1 grain per gallon = grains/gallon 17.1 ppmSimmons Water Fountain6140 ppm X 1 grain per gallon= 8.18 grains/gallon 17.1 ppm* need to multiply by two because of diluting ratio 1:1Table 3: AA standards of Calcium and Magnesium, concentrations, and check standards6Concentration (ppm)Absorbance ValueCa @ 422.76 nmMg @ 202.5 nmCheck Standard(ppm)CalciumMagnesium 0001.000.006311.075.00.046704.9210.00.084879.8825.00.2010624.6450.00.3805450.040001.000.019090.895.00.095355.4110.00.173139.3225.00.3694424.9850.00.4501730.70Both the graphs above show a calibration equation that has been derived from the line of best fit on each graph6. The calibration equations are used to calculate the concentrations of both the ions. Table 3 shows all the data that was used to create the axis and points for the graph, which led to the creation of the calibration equation. Table 4: AA Absorbance and Hardness (ppm) resultsAbsorbance Value (nm)Concentration (ppm)Hardness (ppm)Simmons Water Fountain6Total Hardness-325.32Ca2+.217214.0863.54Mg2+.229431.77261.78Apartment Sink7Total Hardness- 245.45Ca2+.248931.28NAMg2+.172810.82NAPuddle8Total Hardness-282.4Ca2+.240630.72153.6Mg2+.254515.63128.64Shower Water9Total Hardness-294.76Ca2+NANANAMg2+NANANA*NA- Either the values were not given to me or I was not given enough information to calculate them myselfEquation 4: Calculation of Concentration (ppm) from Absorbance Value Using Calibration EquationX= concentrationY = Absorbance ValueCalibration equation Ca2+: y = .014x + .02Calibration equation Mg2+: y = .007x + .007Ca: .2172 = .014x + .02 x = 14.08Mg: .2294 = .007x + .007 x = 31.77Equation 5: Calculation of equivalent concentrationPpm Ca2+ x 100g CaCO3/mol = ppm CaCO3 (hardness) 40.0 g Ca2+/molPpm Mg2+ x 100g CaCO3/mole = ppm CaCO3 (hardness) 23.4 g Mg2+/moleCa2+: 14.08 x 100g CaCO3/mole = 35.2 ppm *multiply by 2 when finding total hardness 40.0 g Ca2+/moleMg2+: 31.77 x 100g CaCO3/mole = 130.89 *multiply by 2 when finding total hardness 23.4 g Mg2+/mole35.2(2) + 130.89(2) = 325.32 ppmTable 5: EDTA results of softened water samplesCommercial Softener (ppm)Resin Beads (ppm)pH of water treated with resinSimmons water fountain 6280205Apartment water724080NAPuddle828040NAShower Water928020NADISCUSSIONFirst we will start out by looking at table 1. The results from the TDS analysis suggest that the puddle and the Simmons drinking water will have the highest water hardness levels then followed by the apartment water and the shower water. Table 2 helps support this point by showing that the puddle had the highest grain per gallons at 23.4 then followed by the shower at 18.7, then the Simmons water fountain close behind at 16.37 and finally the apartment sink at 11. 69.Table 4 switches things up slightly and has the Simmons water fountain overall having the highest total hardness; Although it had the lowest Ca2+ hardness. One can see that the Mg2+ levels were very high in the Simmons water fountain.My hypothesis was correct in some aspects but incorrect in others. Overall I guessed the wrong order of hardness. But some of my predictions did end up being slightly true. I was right about the puddle gathering up calcium and magnesium because you can see that their hardness’s are very close to each other. I was also close in my prediction that the sample from the water fountain and the sample from the shower would be similar. There was only a difference of about 25 ppm, which is only a difference in in well in the 12 well tray6. The two samples with the highest hardness values ended up being the Simmons Hall water fountain and the East Halls showers. Now that I think about it, it makes sense because both the shower and the water fountain are used throughout the day everyday, which would account for a high amount of buildup, which would contribute to the hardness10.Next we have the results from the commercial water softener. The water softener worked for all the samples but some more than others. For both the puddle and the apartment sink the hardness with the softener compared to with out the softener was barely different. The apartment sinks hardness only dropped 5.45 ppm while the puddle only dropped 2.4 ppm. On the other hand the softener worked decently for the shower water dropping its hardness 14.76 ppm. The water softener worked best on the water fountain water though dropping it 45.32 ppm. The varied results could be two where the ideal range for ppm is. Three of the four members of the group got 280 as their ppm for after the softener was used. The fluctuation in the effectiveness of the softener could be a result of the softener attempting to reach an ideal hardness.Unfortunately Pennsylvania State University does not keep records of the water hardness of its shower water and drinking water and neither does the apartment complex that we received the sink water from. Also it is hard to tell what the actual hardness of the puddle water is because so many factors go into how much Ca2+ and Mg2+ got into the puddle water in that given amount of time. Of course without any of the actual values of hardness known it is hard to say what we did wrong if anything, although there is always room for error. Possible errors could have come from not being able to accurately pinpoint where the titration should have ended. In EDTA titration you are going of color change and where you believe the color changes enough to be considered the turning point. If you are off by a single well than your results will vary in all your calculations from there on because you are using an incorrect value. Another possible error could have come during the softener process. There were some significant changes in the hardness while there were some that were barely noticeable. This could be a result of everyone doing the experiment by themselves and each person using a slightly different amount of softener. As all chemists know, even a slight difference in mass can throw off you results. In the end, of the two methods we used AA spectrophotometry is the more precise technique. In almost every scenario a machine will work better in determining something than the human judgment. AA spectrophotometry is also much faster and more efficient. CONCLUSIONMost of the water samples we took were all from the same area and this might be one of the main factors that explain why all the measurements of hardness we got was similar. After all the results were in the hardest of all the waters was the Simmons Hall water fountain (325.52ppm) followed by the East Halls shower water (294.76ppm), then the puddle (282.4ppm) and finally the apartment sink water (245.45ppm) The results make sense as one would expect the shower water and water fountain water to be close because they both come from Penn State’s water source. All the samples ended up being above 180ppm, which made them very hard. This also makes sense because as previously stated research has shown drinking hard water is indeed better for you than drinking soft water.REFERENCES1. Ko?ak N, Güle? M, Tekba? ?F. [Water Hardness Level and It’s Health Effects]. ?mno=1566 [Access: November 7, 2012]. Turkish.?doi:10.5455/pmb.201011240534322. PSU Chemtrek; Stephen Thompson, Ed.; Prentice Hall: Englewood, NJ, 2012-2013 version Chapter 103. Fairfax County Water Authority. "Explanation of Water Hardness." NAV. Web. Nov 7. < Casiday, Rachel. "Water Hardness."?Water Hardness. Washington University, 1998. Web. 7 Nov. 2012. <. Brown, Lemay, and Buster.?Chemistry: the Central Science, 7th ed. Upper Saddle River, NJ: Prentice Hall, 1997. p. 681-36. Torres, Ben. Chem 111 Lab Notebook Pg 32-367. White, Alicia. Chem 111 Lab Notebook Pg 32-368. Wertman, Matt. Chem 111 Lab Notebook Exp 10 Notes9 Wertz, Bobby. Chem 111 Lab Notebook Exp 10 Notes10. "Hardness in Your Drinking Water."?Water Systems Council. N.p., July 2004. Web. 6 Nov. 2012. <. "Science Notes/Chemistry."?Lexis Nexis. The Buffalo News, 2011. Web. 7 Nov. 2012. <(Science+notes+%2F+Chemistry)+and+date+is+November+13%2C+2011>. ................
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