Experiment 2 – Water Analysis I

| September 13, 2019

Experiment 2 – Water Analysis I. Purpose Analyze different water samples qualitatively and quantitatively. Use Vernier electrodes and sensors to digitally collect data and create plots. Practice physical methods of separation and purification, such as distillation. II. Introduction Although Earth has an abundance of water, about 97% is seawater. The high concentration of sodium chloride in seawater makes it unsuitable to consume. Drinking seawater typically causes dehydration and diarrhea since most of the body fluids move out of the cells and into the intestine. Most of the drinking water comes from lakes and rivers. But less than 0.01% of this water is naturally available. The quantity of drinking water becomes scarcer as lakes and rivers are polluted by biological and chemical contaminants. Polluted water was especially a controversy in London, 1854, when contaminated drinking water caused the death of many lives. It is important to be able to purify and analyze water. III. Materials Part 1. Water Distillation & Analysis Distillation Apparatus Boiling Chips Conductivity Device 0.1 M NaCl 0.1 M AgNO3 0.1 M SrCl2 Nichrome Wire 6 M HCl 50-mL Buret Standardized 0.005 M EDTA Ammonia-ammonium Chloride Buffer Eriochrome Black T Indicator Part 2. Water Analysis with Probes Conductivity Probe Vernier Turbidity Sensor Vernier pH Sensor Turbidity Cuvette pH 7 Buffer Solution Soft, Lint-free Cloth or Tissue pH 10 Buffer Solution Vernier Computer Interface Laptop Computer Vernier Temperature Probe Logger Pro Software Chloride Ion-Selective Electrode – Low Standard (10 mg/L Cl ) High Standard (1000 mg/L Cl–) Low Standard (10 mg/L Ca2+) High Standard (1000 mg/L Ca2+) Calcium Ion-Selective Electrode Turbidity Standard (StableCal® Formazin Standard 100 NTU) IV. Safety Precautions Be careful with the handling of acids and bases used in this experiment, especially 6M HCl. Normal precautions for dilution processes should be observed. 18 V. Experimental Procedure Part 1. Water Distillation & Analysis Thermometer Distillation Head Utility Clamp Condenser Distillation Adapter Distilling Flask Utility Clamp Water Out Water In Figure 2A: A distillation apparatus. A. Distillation 1. Assemble a distillation apparatus similar to the illustration above (Figure 2A). It is important to clamp the distilling flask and condenser to avoid dropping these expensive parts. 2. Once the distillation apparatus is set up, fill the distilling flask with tap water to about half full. Make sure to add several (about 3 – 5) boiling chips into the distilling flask to avoid bumping. 3. With the rubber hoses attached to the condenser, allow water to flow continuously in from the lower to the upper part of the condenser. From the upper part of the condenser, make sure that water flows smoothly out into the sink. 4. Begin heating the distilling flask with a flame from a Bunsen burner. 19 5. Discard the first 25 drops of distilled water collected as they may contain contaminates from the apparatus. 6. Monitor the water level in the distilling flask while collecting distilled water. When the water level is low in the distilling flask, add more tap water. B. Conductivity Test 1. Pour approximately 25 mL of the distilled water collected from the distillation into a clean and dry 50 mL beaker. 2. Into a different clean and dry 50 mL beaker, pour about 25 mL of tap water. 3. Repeat the same procedure with 0.1 M NaCl and deionized water. 4. Using a conductivity meter, test the conductivity of each of the 4 samples. Make sure to clean the electrodes of the conductivity meter with deionized water between each sample. C. Chloride Test 1. Pour approximately 1 mL of the distilled water collected from the distillation into a clean and dry test tube. 2. Into a different clean and dry test tube, pour about 1 mL of tap water. 3. Repeat the same procedure with 0.1 M NaCl and deionized water. 4. Into each of the 4 samples, add 2 drops of 0.1 M AgNO3 and mix. D. Flame Test 1. To prepare your sample, pour approximately 2 mL of the distilled water collected from the distillation into a clean and dry test tube. 2. Into a different clean and dry test tube, pour about 2 mL of tap water. 3. Repeat the same procedure with 0.1 M NaCl, deionized water, and 0.1 M SrCl2. 4. Dip a nichrome wire into a test tube containing approximately 3 mL of 6 M HCl. 5. Flame the nichrome wire using a Bunsen burner. Make sure to flame the nichrome wire at the top of the blue inner cone of the flame. 6. Repeat the dipping and flaming process at least two more times to make sure the nichrome wire is clean. 20 7. After cleaning, dip the nichrome wire into the test tube containing distilled water and insert the wire into the flame of a Bunsen burner. Make sure to flame the nichrome wire at the top of the blue inner cone of the flame. Observe the color of the flame. 8. Repeat the nichrome wire cleaning process and test the next test tube containing tap water. 9. Continue to perform a flame test on the remaining samples, but make sure to clean the nichrome wire between each sample. E. Water Hardness 1. To prepare your sample, rinse a 50-mL buret with tap water and fill the buret with tap water to nearly the markings of “0”. Do not fill the buret to “0”. 2. After recording the initial volume from the buret, dispense 25-mL of the tap water into a clean and dry 250-mL Erlenmeyer flask and record the final volume. The actual volume dispensed is equal to the final volume reading minus the initial volume reading. 3. Into the Erlenmeyer flask, add 20 drops of ammonia-ammonium chloride buffer, 2 drops of eriochrome Black T indicator, and swirl to mix the mixtures. 4. Rinse a 50-mL buret with approximately 5-mL of 0.005 M EDTA and allow the rinse to flow through the buret into a 150-mL beaker. The 150-mL beaker will serve as a waste container. 5. Repeat the rinse procedure once more. 6. After the second rinse, fill the buret with 0.005 M EDTA to nearly the markings of “0”. Again, do not fill the buret to “0”. Record the initial volume from the buret. 7. Add one drop at a time the EDTA solution from the buret into the 250-mL Erlenmeyer flask containing the sample prepared in steps 1-3. Make sure to swirl the Erlenmeyer flask while each drop enters the flask. It is recommended to place a white sheet of paper underneath the flask as this will aid in the observation of color changes. As the end point approaches, the red color begins to turn blue. It is important to slowly add one drop at a time, especially near the end point. The end point is reached when the red color changes to blue and remains blue for at least thirty seconds. 8. Record the final volume of the buret once the end point is achieved. 9. Repeat the procedure with the distilled water collected from the distillation as a different sample. 10. Perform another repeat with deionized water as the third sample. 21 F. Calculations Although calcium and magnesium ions can be present in the 3 samples, assume that only calcium ions are present to calculate the hardness of water in each sample. Use the following formula: hardness of water in ppm = (volume in mL of EDTA used) x 500 volume in mL of water sample used Part 2. Water Analysis with Probes A. Sample Preparation 1. Pour approximately 25 mL of the distilled water collected from the distillation into a clean and dry 50 mL beaker. 2. Into a different clean and dry 50 mL beaker, pour about 25 mL of tap water. 3. Repeat the same procedure with 0.1 M NaCl and deionized water. B. Total Dissolved Solid Measurement 1. Using a Conductivity Probe, measure one sample at a time the total dissolved solid (TDS) value of the 4 samples from the “Sample Preparation” procedure. 2. Into the 50 mL beaker of each sample, insert the Conductivity Probe and set the switch on the Conductivity Probe box to 0–2000 µS/cm (2000 µS/cm = 1000 mg/L TDS). Record the value in mg/L. (*Note: Make sure to rinse the Conductivity Probe with deionized water between each sample.) C. Temperature Measurement Make sure to position the computer as far away as possible from any liquids. 1. Plug the Temperature Probe into Channel 1 of the Vernier interface. 2. On the computer, open “01 Temperature” from the Water Quality with Vernier experiment folder of Logger Pro. 3. Using the Temperature Probe, measure one sample at a time the temperature of the 4 samples from the “Sample Preparation” procedure. 4. Into the 50 mL beaker of each sample, insert the Temperature Probe. 5. On the computer, click “collect” to begin data collection. Click “Keep” to begin a 10 second sampling run. 6. After 10 seconds, stop data collection and record the average temperature. (*Note: Make sure to rinse the Temperature Probe with deionized water between each sample.) 22 D. pH Analysis pH Sensor Setup 1. Plug the pH Sensor into Channel 1 of the Vernier interface. 2. On the computer, open “02 pH” from the Water Quality with Vernier experiment folder of Logger Pro. pH Sensor Calibration 3. On the computer, choose “Calibrate > CH1: pH” from the Experiment menu and then click “Calibrate Now.” 4. Remove the pH Sensor from the bottle by loosening the lid. 5. Rinse the pH Sensor with deionized water. Using “Kimwipe” or soft tissue, gently blot the pH Sensor dry. 6. Insert the pH Sensor tip into the pH-7 buffer solution. On the computer, type “7” in the edit box. This number represents the pH value of the buffer. When the voltage reading for Reading 1 stabilizes, click “Keep”. 7. Rinse the pH Sensor with deionized water. Using “Kimwipe” or soft tissue, gently blot the sensor dry. 8. Insert the pH Sensor into the pH-10 buffer solution. On the computer, type “10” in the edit box. When the voltage reading for Reading 2 stabilizes, click “Keep”, then click “Done”. pH Measurement 9. Remove the pH Sensor from the buffer solution and rinse it with deionized water. Using “Kimwipe” or soft tissue, gently blot the pH Sensor dry. 10. Using the pH Sensor, measure one sample at a time the pH of the 4 samples from the “Sample Preparation” procedure. Into the 50 mL beaker of each sample, insert the pH Sensor. On the computer, click “collect” to begin data collection. Click “Keep” to begin a 10 second sampling run. After 10 seconds, stop data collection and record the average pH. (*Note: Make sure to rinse the pH Sensor with deionized water between each sample.) E. Turbidity Analysis Turbidity Sensor Setup 1. Make sure to position the computer as far away as possible from any liquids. Plug the Turbidity Sensor into Channel 1 of the Vernier interface. 2. Allow the Turbidity Sensor to warm up for 2 minutes. 23 3. On the computer, open “03 Turbidity” from the Water Quality with Vernier experiment folder of Logger Pro. Turbidity Sensor Calibration 4. On the computer, choose “Calibrate > CH1: Turbidity (NTU)” from the Experiment menu and then click “Calibrate Now.” 5. Prepare a “blank” by rinsing the glass turbidity cuvette with deionized water. Fill the glass turbidity glass cuvette with deionized water until the bottom of the meniscus is exactly at the top of the white line. 6. Place the lid on the cuvette. Using “Kimwipe” or soft tissue, gently wipe the outside of the cuvette dry. If air bubbles are present in the cuvette, gently tap the bottom of the cuvette on a hard surface to remove the air bubbles. 7. Holding the cuvette by the lid, insert it into the Turbidity Sensor. Make sure that the mark on the cuvette is aligned with the mark on the Turbidity Sensor. 8. Close the lid on the Turbidity Sensor. 9. On the computer, type “0” in the edit box. When the voltage reading for Reading 1 stabilizes, click “Keep”. Remove the cuvette from the Turbidity Sensor. 10. Obtain the cuvette containing the Turbidity Standard (100 NTU) and gently invert it 5 times to mix any particles that may have settled to the bottom. (*Note: Do not shake the cuvette as air bubbles may appear!) Using “Kimwipe” or soft tissue, gently wipe the outside of the cuvette. 11. Holding the cuvette by the lid, insert it into the Turbidity Sensor. Make sure that the mark on the cuvette is aligned with the mark on the Turbidity Sensor. 12. Close the lid of the Turbidity Sensor. 13. On the computer, type “100” in the edit box. When the voltage reading for Reading 2 stabilizes, click “Keep”, then click “Done”. Remove the cuvette from the Turbidity Sensor. Turbidity Measurement 1. Pour out the deionized water from the cuvette used as a “blank.” 2. Rinse the cuvette with the distilled water collected from the distillation. 3. Fill the cuvette with the distilled water so that the bottom of the meniscus is exactly at the top of the white line. 4. Place the lid on the cuvette. 24 5. Using “Kimwipe” or soft tissue, gently wipe the outside of the cuvette dry. If air bubbles are present in the cuvette, gently tap the bottom of the cuvette on a hard surface to remove the air bubbles. 6. Holding the cuvette by the lid, insert it into the Turbidity Sensor. Make sure that the mark on the cuvette is aligned with the mark on the Turbidity Sensor. Close the lid on the Turbidity Sensor. 7. On the computer, click “Collect” to begin data collection. Click “Keep” to begin a 10 second sampling run. After 10 seconds, stop data collection and record the average turbidity. 8. Remove the cuvette from the Turbidity Sensor. 9. Rinse the cuvette with tap water and fill the cuvette with tap water so that the bottom of the meniscus is exactly at the top of the white line. 10. Repeat the procedures as before to measure the turbidity of tap water. F. Chloride and Salinity Analysis Chloride Ion-Selective Electrode (ISE) Setup 1. The ISE should be soaking in the High Standard (1000 mg/L Cl–). Make sure that it is not resting on the bottom of the container, but ensure that the small white reference contacts are immersed. 2. Plug the ISE Sensor into Channel 1 of the Vernier interface. 3. On the computer, open “15 Chloride ISE” from the Water Quality with Vernier experiment folder of Logger Pro. Chloride ISE Calibration 4. On the computer, choose “Calibrate > CH1: Chloride ISE” from the Experiment menu and then click “Calibrate Now”. 5. Type “1000” in the edit box. This represents the concentration in mg/L Cl–. When the voltage reading for Reading 1 stabilizes, click “Keep.” 6. Remove the electrode from the High Standard and rinse the electrode with deionized water. 7. Using “Kimwipe” or soft tissue, gently blot the electrode dry. Insert the tip of the electrode into the Low Standard (10 mg/L Cl–). Again, make sure that it is not resting on the bottom of the container but ensure that the small white reference contacts are immersed. 25 8. Make sure no air bubbles are trapped below the electrode. 9. After gently swirling the solution, hold the ISE still and wait about 30 seconds for the voltage reading on the computer to stabilize. 10. Type “10” in the edit box. When the voltage reading for Reading 2 stabilizes, click “Keep”, then click “Done”. Chloride Measurement 11. Remove the electrode from the Low Standard and rinse the electrode with deionized water. 12. Using “Kimwipe” or soft tissue, gently blot the electrode dry. 13. Insert the tip of the electrode into a 50 mL beaker containing distilled water collected from the distillation. Again, make sure that it is not resting on the bottom of the container but ensure that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the electrode. 14. On the computer, click “Collect” to begin data collection. 15. Click “Keep” to begin a 10 second sampling run. After 10 seconds, stop data collection and record the average chloride concentration. 16. Remove the electrode from the distilled water sample and rinse the electrode with deionized water. 17. Using “Kimwipe” or soft tissue, gently blot the electrode dry. Insert the tip of the electrode into a 50 mL beaker containing tap water. 18. Repeat the procedures as before to measure the chloride concentration in tap water. Salinity Value Determination 19. Use the following formula to calculate the salinity in ppt for each sample. salinity (ppt) = 0.0018066 x Cl– (mg/L) G. Water Hardness Calcium Ion-Selective Electrode (ISE) Setup 1. The ISE should be soaking in the High Standard (1000 mg/L Ca2+). 2. Plug the ISE Sensor into Channel 1 of the Vernier interface. 26 3. On the computer, open “13 Calcium & Hardness” from the Water Quality with Vernier experiment folder of Logger Pro. Calcium ISE Calibration 4. On the computer, choose “Calibrate > CH1: Calcium ISE (mg/L)” from the Experiment menu and then click “Calibrate Now”. 5. Type “1000” in the edit box. This represents the concentration in mg/L Ca2+. 6. When the voltage reading for Reading 1 stabilizes, click “Keep”. 7. Remove the electrode from the High Standard and rinse the electrode with deionized water. 8. Using “Kimwipe” or soft tissue, gently blot the electrode dry. 9. Insert the tip of the electrode into the Low Standard (10 mg/L Ca2+). Again, make sure no air bubbles are trapped below the electrode. 10. After gently swirling the solution, hold the ISE still and wait about 30 seconds for the voltage reading on the computer to stabilize. Type “10” in the edit box. When the voltage reading for Reading 2 stabilizes, click “Keep”, then click “Done”. Calcium Measurement 11. Remove the electrode from the Low Standard and rinse the electrode with deionized water. 12. Using “Kimwipe” or soft tissue, gently blot the electrode dry. 13. Insert the tip of the electrode into a 50 mL beaker containing distilled water collected from the distillation. 14. On the computer, click “Collect” to begin data collection. 15. Click “Keep” to begin a 10 second sampling run. After 10 seconds, stop data collection and record the average calcium concentration. 16. Remove the electrode from the distilled water sample and rinse the electrode with deionized water. Using “Kimwipe” or soft tissue, gently blot the electrode dry. 17. Insert the tip of the electrode into a 50 mL beaker containing tap water. 18. Repeat the procedures as before to measure the calcium concentration in tap water. 27 Water Hardness Determination 19. Convert the calcium concentration (mg/L Ca2+) to units of calcium hardness (mg/L as CaCO3). The calculation takes into account the molar mass for both Ca2+ and CaCO3. Use the following formula to calculate the calcium hardness as CaCO3 for each sample. calcium hardness as CaCO3 = (mg/L Ca2+) x (100 g CaCO3 / 40 g Ca2+) = (mg/L Ca2+) x 2.5 VI. Questions 1. If the endpoint is reached when 50.00 mL of a tap water sample is titrated with 12.00 mL of 5.00 x 10–3 M EDTA solution, what is the hardness of the water sample in ppm? VII. Discussion Questions 1. In part 1, “Water Distillation & Analysis”, is there a correlation between the various techniques used to analyze the samples of distilled water, tap water, deionized water, and 0.1 M NaCl? Explain. VIII. References 1. Baird, C. and M. Cann, Environmental Chemistry, The Chemistry of Natural Waters (2008) 4th ed., W.H. Freeman and Company. 2. Murov, S., Experiments in General Chemistry, Water Purification and Analysis, (2006) 5th Ed., Thomson Brooks/Cole 3. Paneth, N., Assessing the Contributions of John Snow to Epidemiology. Epidemiology, 2004. 15(5): p. 514-516. 4. Randall, J., Advanced Chemistry with Vernier (2007) 2nd Ed., Vernier Software & Technology, Beaverton, OR 5. Tro, N.J., Chemistry: A Molecular Approach, Thirsty Solutions: Why You Should Not Drink Seawater. (2011) 2nd ed., Prentice Hall. 28 …
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