FINAL REPORT A Mini Grant for Redesigning Lab Experiments for "Chemistry in Society" (ACHM 105) - A General Education Course Kutty Pariyadath

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1 FINAL REPORT A Mini Grant for Redesigning Lab Experiments for "Chemistry in Society" (ACHM 105) - A General Education Course Kutty Pariyadath Introduction The primary purpose of the Mini Grant was to introduce tested, environmental chemistry laboratory exercises into the lab portion of CHEMISTRY IN SOCIETY, ACHM 105, a general education course that is currently offered by the chemistry department at the University of South Carolina Aiken. Funds from the mini grant were used to test several new lab exercises in Summer Most of these tested lab exercises (listed in Table 1) were initially added to the ACHM 105 syllabus in Fall It was apparent that some experiments were clearly more student-friendly than others. Students had little or no difficulty in using the programmable calculators since they were already introduced to these in their algebra classes. As a result, they were able to adapt to the use of Calculator-based lab exercises without much trouble. However, the fact remains that chemistry is not one of favorite subjects of most of those who take this course to fulfill their general education requirements. Therefore, it was decided that the exercises in Table 1 would be introduced is stages so that the instructor(s) could monitor the student response to each exercise. Accordingly, five exercises from Table 1, all involving the use of CBL were added to the Fall 2001 syllabus. These five were, ph measurements using CBL, determination of iron in vitamins using CBL, determination of chloride, nitrate and ammonium ion in water from the Hopeland Gardens using ion selective electrodes and CBL. Hopeland Gardens in Aiken has ponds which receive runoff water from nearby areas. Clearly, analyses of water from the Hopeland Gardens would give these students an example of application of chemistry in real life. Determination of iron in vitamin was chosen instead of iron in pond water, as was originally planned, because there is more measurable iron in multivitamin than in pond water. Implementation of Lab Exercises During the first round of implementation, water from the Hopeland Gardens was collected on the day of the experiment and its ph, chloride, ammonium and nitrate contents were measured using a calculator based lab interface (CBL) from Vernier Software, a TI-83 calculator and the appropriate Vernier-developed Ion Selective Electrodes (ISE). Though the experiments were done with some degree of success, the limited number of ISE probes made it difficult to conduct the experiment in a large class. Ion selective electrodes are sensitive to the way they are handled and both the students and the instructor needed more practice than time permitted in that semester. They were

2 tried during the summer session with more success and have been included in the current syllabus (Spring 2003). Iron content of a solid multivitamin tablet was determined using the CBL system including a Vernier-developed colorimetric probe. Filtration of the binding agent was difficult. This problem was solved by using a liquid sample of a multivitamin in place of the solid. Most of the students were able to get reasonably good data using the liquid vitamin. After being a part of the syllabus for the past 4 semesters, including summer 2002, this experiment has now become a permanent part of ACHM 105 lab. The determination of iron content in a multivitamin tablet worked well though filtering off the binding agent to get a clear liquid that was needed for analysis was difficult. A switch to a liquid vitamin in Spring 2002 worked well and this lab exercise has now become an integral part of this course. The exercises involving the ISE's were carried out in the Summer 2002 session which only had 11 students. In this smaller class environment these exercises were more successful. Yet, it was clear that these needed closer supervision than was available in a class with one instructor and 24 students. Table 1 Week Name 1. Weighing Air and Cooling Water 2. Comparison of the Energy Content of Fuels using CBL temperature probe 3. Chemical Bonds Molecular Models and Molecular Shapes 4. Measurement of Water Hardness with CBL calcium electrode probe 5. Measurement of Chloride in Tap Water with CBL chloride electrode probe 6. ph Measurement of Common Household Chemicals with CBL ph probe 7. Total Dissolved Solids with CBL conductivity probe 8. Analysis of Iron in Tap water with CBL colorimetric probe Analysis of Drinking Water for Iron, Hardness, Chloride, ph, Conductivity, Nitrate, and Dissolved Oxygen Analysis of Water from the Hopeland Gardens for Dissolved Oxygen, ph, Chloride, Nitrate, Hardness, Dissolved Solids

3 Future Implementation This mini grant has allowed the chemistry department at USCA to introduce some technology and experimental techniques relevant to environmental chemistry into its general chemistry course (ACHM 105) intended for nonscience majors. The department will continue to refine all of these lab exercises so that those that were not successful in the first round of implementation may be included at some time in the future. The department has been able to acquire more Ion Selective Electrodes more recently and this should make addition of this tool to the lab exercises in ACHM 105 a definite possibility. Acknowledgement The recipient of the mini grant, Kutty Pariyadath, thanks the Dr. Bruce Coull, Dean of School of the Environment

4 INTRODUCTION Ammonium Nitrogen The ammonium ion, NH 4 +, is an important member of the group of nitrogen-containing compounds that act as nutrients for aquatic plants and algae. In surface water, most of the ammonia, NH 3, is found in the form of the ammonium ion, NH 4 +. This fact allows us to approximate the concentration of all of the nitrogen in the form of ammonia and ammonium combined, commonly called ammonia nitrogen, by measuring only the concentration of the ammonium ions. All plants and animals require nitrogen as a nutrient to synthesize amino acids and proteins. Most nitrogen on earth is found in the atmosphere in the form of N 2, but plants and animals cannot utilize it in this form. The nitrogen must first be converted into a useable form, such as nitrate, NO 3. These conversions among the various forms of nitrogen form a complex cycle called the nitrogen cycle. In the nitrogen cycle, bacteria convert atmospheric nitrogen into ammonium in a process called nitrogen fixation. This process often occurs in the roots of leguminous plants such as alfalfa, beans, and peas. Bacteria can also convert the nitrogen in decaying plant and animal matter and waste products in the soil or water to ammonium in a process called ammonification. Other sources of organic matter for ammonification include industrial waste, agricultural runoff, and sewage treatment effluent. Sources of Ammonia Decaying plants and animals Animal waste Industrial waste effluent Agricultural runoff Atmospheric nitrogen Some trees and grasses are able to absorb ammonium ions directly, but most require their conversion to nitrate. This process, called nitrification, is usually accomplished by bacteria in the soil or water. In the first step of nitrification, ammonium ions are oxidized into nitrite. The nitrite is then converted into nitrate, which can subsequently be utilized by plants and algae. Animals require nitrogen as well. They obtain the nitrogen they need by eating plants or by eating other animals, which in turn have eaten plants. If ammonium nitrogen levels in surface waters are too high, they can be toxic to some aquatic organisms. If the levels are only moderately high, plant and algal growth will usually increase due to the abundance of nitrogen available as a nutrient. This will have a ripple effect on other attributes of water quality, such as increasing biochemical oxygen demand and lowering dissolved oxygen levels. Dissolved oxygen levels can also be lowered when ammonium nitrogen is high due to the increased amount of nitrification occurring. Effects of Ammonium Levels High levels - eutrophication - increased algal blooms - increased BOD - decreased DO - toxic to some organisms Low levels - limiting factor in plant and algal growth If enough nutrients are present, eutrophication may occur. Eutrophication occurs when there is such an abundance of nutrients available that there is

5 a significant increase in plant and algal growth. As these organisms die, they will accumulate on the bottom and decompose, releasing more nutrients and compounding the problem. In some cases, this process of eutrophication can become so advanced that the body of water may become a marsh, and eventually fill in completely. If too little ammonium nitrogen is present, it may be the limiting factor in the amount of plant and algal growth. Ammonium nitrogen can quickly be converted into nitrites or nitrates; therefore, a low level of ammonium-nitrogen does not necessarily indicate a low level of nitrogen in general. Expected Levels Ammonium-nitrogen levels are usually quite low in moving surface waters. This is because there is little decaying organic matter collecting on the bottom. If there is a high level of ammonium nitrogen in a moving stream, it may be an indication of pollution of some kind entering the water. Ponds and swamps usually have a higher ammonium nitrogen level than fast-flowing water. While levels of ammonium nitrogen in drinking water should not exceed 0.5 mg/l, streams or ponds near heavily fertilized fields may have higher concentrations of this ion. Fertilizers containing ammonium sulfate, (NH 4 ) 2 SO 4, or ammonium nitrate, NH 4 NO 3, may result in runoff from fields containing a high level of ammonium ions. Summary of Method Table 1: Ammonium Levels of Selected Rivers A Vernier Ammonium Ion-Selective Electrode (ISE) is used to measure the concentration of ammonium nitrogen in the water, either on site or after returning to the lab. Site Ammonium (mg/l NH 4 + -N) Mississippi River, Memphis, TN 0.07 Hudson River, Poughkeepsie, NY 0.08 Colorado River, Hoover Dam, AZ-NV 0.03 Willamette River, Portland, OR 0.09 Platte River, Louisville, NE 0.24 Materials Checklist CBL System TI Graphing Calculator CHEMBIO program Vernier adapter cable calculator-to-cbl link cable Ammonium Ion-Selective Electrode Vernier ISE Amplifier small paper or plastic cup (optional) tissue paper or paper towels wash bottle with distilled water Low Standard (1 mg/l NH + 4 -N) High Standard (100 mg/l NH + 4 -N)

6 Advanced Preparation The Vernier Ammonium Ion-Selective Electrode (ISE) should be soaked in the Ammonium High Standard solution (included with the ISE) for approximately 30 minutes. Important: Make sure the ISE is not resting on the bottom, and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the ISE. If the ISE needs to be transported to the field during the soaking process, use the ISE soaking bottle. Remove the cap from the ISE soaking bottle and fill the bottle ¾ full with High Standard. Slide the cap onto the ISE, insert it into the bottle, and tighten. Important: Do not leave the ISE soaking for more than 24 hours. Long-term storage should be in a dry environment. Collection and Storage of Samples 1. This test can be conducted on site or in the lab. A 100-mL water sample is required. 2. It is important to obtain the sample water from below the surface of the water and as far away from shore as is safe. If suitable areas of the stream appear to be unreachable, samplers consisting of a rod and container can be constructed for collection. 3. If the testing cannot be conducted within a few hours, place the samples in an ice chest or a refrigerator. Testing Procedure 1. Prepare the Ammonium Ion-Selective Electrode (ISE) for data collection. a. The ISE should be soaking in the High Standard. Make sure that it is not resting on the bottom of the container, and that the small white reference contacts are immersed. b. Plug the ISE Amplifier into the adapter cable in Channel 1 of the CBL System. Connect the Ammonium ISE to the ISE Amplifier. c. Connect the CBL System to the TI Graphing Calculator using the link cable. Firmly press in the cable ends. 2. Turn on the CBL and the calculator. Start CHEMBIO and proceed to the MAIN MENU. 3. Set up the calculator and CBL for the Ammonium ISE. a. Select SET UP PROBES from the MAIN MENU. b. Enter 1 as the number of probes. c. Select ION SELECTIVE from the SELECT PROBE menu. (This will require selecting MORE PROBES several times.) d. Select AMMONIUM ISE from the SELECT PROBE menu. e. Enter 1 as the channel number. 4. Calibrate the CBL and Ammonium ISE. To do this, select PERFORM NEW from the CALIBRATION menu. Follow the directions on the calculator screen to allow the system to warm up, then press ENTER.

7 First Calibration Point a. Make sure the voltage reading on the CBL is stable and press TRIGGER on the CBL. b. Enter 100 (the concentration of the standard) on the calculator. Second Calibration Point c. Rinse the ISE thoroughly with distilled water and gently blot it dry with a tissue. Be very gentle when blotting the membrane. Important: Failure to carefully rinse and dry the ISE will contaminate the standard. d. Place the tip of the ISE into the Low Standard (1 mg/l NH 4 + -N). Be sure that the ISE is not resting on the bottom of the bottle and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the ISE. e. After briefly swirling the solution, hold the ISE still and wait approximately 30 seconds for the voltage reading displayed on the CBL screen to stabilize. Press TRIGGER on the CBL. d. Enter 1 (the concentration) on the calculator. e. Press ENTER to return to the MAIN MENU. 5. Set up the calculator and CBL for data collection. a. Select COLLECT DATA from the MAIN MENU. b. Select MONITOR INPUT from the DATA COLLECTION menu. 6. To collect ammonium concentration data: a. Rinse the ISE with distilled water and gently blot dry. b. Place the tip of the ISE into the sample water. Make sure the ISE is not touching the bottom of the container and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the ISE. c. After briefly swirling the solution, hold the ISE still and wait until the voltage reading displayed on the CBL screen to stabilize. d. Record this value on the Data & Calculations sheet (round to the nearest 0.1 mg/l). Note: The sensor does not read accurately below 0.1 mg/l. If the reading is less than 0.1, write < 0.1 in the appropriate box on the Data & Calculations sheet. e. Remove the ISE from the test solution, rinse with plenty of deionized water, and pat it gently to dry the electrode. f. To get the ammonium nitrogen in a second test solution, place the ISE in that solution and wait till the number on the calculator has stabilized. g. Clean the ISE as before. h. Press ENTER, then select NO to return to the MAIN MENU. i. Move on to the next station.

8 DATA & CALCULATIONS Ammonium Nitrogen Column A Reading NH 4 + -N (mg/l) 1 2 Test Completed: Date: How the Ammonium Ion-Selective Electrode Works The Ammonium Ion-Selective Electrode is a membrane-based electrode that measures ammonium ions in an aqueous solution. The membrane is a porous plastic disk, permeable to the ion exchanger, but impermeable to water. When the membrane of the ISE is in contact with a solution containing the ammonium ion, a voltage, dependent on the level of ammonium in the solution, develops at the membrane. The CBL reads the voltage and calculates the ion concentration.

9 Determining the Quantity of Iron in Multivitamins Introduction Iron is an essential element present in several forms and participating in many crucial biochemical activities in the human and animal bodies. For example iron in the blood is necessary for transporting oxygen to different parts of the body. Iron is present in many of the foods, and often supplemented through the consumption of iron-fortified vitamin tablets. In this experiment you will determine the amount of iron present in multivitamin (supplied as a liquid) using a technique commonly used by analytical chemists: colorimetry. This technique employs the fact that colored materials absorb visible light. The amount of light absorbed is usually proportional to the amount of the colored compound in the solution. Since the iron-containing vitamin may or may not have color, it has to be mixed with chemicals that will combine with iron and create a distinct color, the intensity of which may then be measured using a colorimeter. The chemical used to develop the color is 1,10 phenanthroline, and all the iron is reduced to the +2 state by hydroxylamine hydrochloride and kept in that state by controlling the ph using sodium acetate. Colorimeter is a device that allows light to go through a solution and measures the light absorbed by collecting data either in the form of % of light transmitted or in the form of absorbance, which is a measure of light absorbed. This absorbance is directly proportional to the amount of iron in solution. What is usually done is to create a calibration curve using known amounts of iron and measuring the absorbance of these known amounts. One then generates a graph with the amount of iron on the x-axis and absorbance on the y-axis. One then measures the absorbance of the iron extract prepared from multivitamin tablets as described in step 2 below. MATERIALS CBL System TI Graphing Calculator Vernier Colorimeter Vernier adapter cable 1.0-mL plastic disposable pipets one cuvette six 20 X 150 mm test tubes test tube rack liquid multivitamin 20 mg/l iron (II) solution 1% hydroxylamine hydrochloride 1 M sodium acetate 1% 1,10 phenanthroline two 10-mL graduated cylinders Deionized water rubber stoppers PROCEDURE Groups of three students may work well for this experiment. 1. Obtain and wear goggles. 2. Your instructor would have the solution of the vitamin with iron ready for you to use. 3. Clean and dry 6 test tubes, and label them 1-6. Label four 1.0-mL plastic pipets A-D. Prepare a set of four standards and one blank solution in 5 test tubes using the following solutions: CAUTION: Handle the solutions with care.

10 A. 20 mg/l iron (II) solution B. 1% hydroxylamine hydrochloride C. 1 M sodium acetate D. 1% 1,10 phenanthroline Note: First add solutions B, C, and D into the numbered test tubes using the labeled plastic 1.0-mL disposable pipets. Volumes to be taken are given in the table below. Add distilled water using a graduate cylinder.. Then add solution A, using the plastic pipet labeled A. Important: Mix each solution thoroughly by closing the test tube with a rubber stopper and then shaking the solution. Use the same rubber stopper again after rinsing it with distilled water. test tube number A (ml) B (ml) C (ml) D (ml) (blank) distilled water (ml) 4. Plug the colorimeter into the adapter cable in Channel 1 of the CBL System (Look at the top end of the CBL unit). Use the link cable to connect the CBL System to the TI-83 Graphing Calculator. Firmly press in the cable ends. 5. Turn on the CBL unit and the calculator. 6. Start the CHEMBIO program by using the PRGM key and presiing the ENTER key. Press ENTER two more times and you should see the MAIN MENU. 7. To set up the calculator and CBL for the colorimeter. Select SET UP PROBES from the MAIN MENU. Enter 1 as the number of probes. Select COLORIMETER from the SELECT PROBE menu. Enter 1 as the channel number. The calculator screen reads "Calibration pt 1; monitor voltage on CBL; when stable push [TRIGGER] 8. You are now ready to calibrate the colorimeter. First prepare a blank by filling a cuvette 3/4 full with the Test Tube 5 solution. To calibrate the cuvette at 0% and 100% transmittance: Place the blank cuvette (using the ridged side of the cuvette to hold it)in the cuvette slot of the colorimeter and close the lid. The smooth side of the cuvette should always face the white line on the colorimeter. Turn the wavelength knob of the colorimeter to the 0% T position. In this position, the light source is turned off, so no light is received by the photocell. When the voltage reading displayed on the CBL screen stabilizes, press TRIGGER on the CBL and enter 0 (under the instruction "Enter reference") in the TI calculator and press ENTER. Turn the wavelength knob of the colorimeter to the Green LED position (565 nm). In this position, the colorimeter is calibrated to show 100% of the green light being transmitted through the blank cuvette. When the displayed voltage reading stabilizes, press TRIGGER and enter 100 (under the instruction "Enter reference") in the calculator and press ENTER. Leave the wavelength knob of the colorimeter set to the Green LED position for the remainder of the experiment. 9. Set up the calculator and CBL for data collection. Select COLLECT DATA from the MAIN MENU. 2

11 Select TRIGGER/PROMPT from the DATA COLLECTION menu. 10. You are now ready to collect absorbance-concentration data for the four standard solutions. Empty the 'blank' solution from the cuvette. Using the Test Tube 1 solution, rinse the cuvette twice with ~1-mL amounts and then fill it 3/4 full. Wipe the outside with a tissue and place it in the colorimeter. After closing the lid, wait for the percent transmittance value displayed on the CBL screen to stabilize. Then press TRIGGER and enter 2.00 (the iron concentration, in mg/l) in the TI calculator and press ENTER. The absorbance and concentration values have now been saved for the first solution. Select MORE DATA from the options on the calculator. 11. Pour the cuvette contents into the waste container at you work lab bench. Rinse the cuvette twice with the Test Tube 2 solution and fill the cuvette 3/4 full. Wipe the outside, place it in the colorimeter, and close the lid. When the percent transmittance value displayed on the CBL has stabilized, press TRIGGER and enter 4.00 in the calculator. 12 Repeat the Step 11 of procedure to save the absorbance and concentration values of the Test Tube 3 solution (6.00 mg/l) and Test Tube 4 (8.00 mg/l). When finished with Test Tube 4, select STOP and GRAPH from the DATA COLLECTION menu. Select STOP AND GRAPH from the DATA COLLECTION menu when you have finished collecting data. Examine the data points along the displayed graph of absorbance vs. concentration. As you move the cursor right or left, the concentration (X) and absorbance (Y) values of each data point are displayed below the graph. Record the absorbance and concentration data pairs in your data table. 13. Use Test Tube 6 to prepare the vitamin sample for absorbance measurement by following a procedure similar to step 3 above. Add 1.00 ml of the vitamin solution given to you with a fresh 1.0-mL plastic pipet and then add 1 ml each of solutions B, C, and D to the test tube using plastic pipets that were used for these solutions. Add 6.0 ml of deionized water with a graduate cylinder and stopper and mix the solution. Rinse the cuvette twice with the sample solution and fill it about 3/4 full. Wipe the outside of the cuvette, place it into the colorimeter, and close the lid. CAUTION: Handle the solutions with care. 14. To find the absorbance of the sample solution: Press ENTER The screen reads REPEAT 1. NO 2. Yes Select NO and press ENTER to return to the MAIN MENU. Important: Do not select SET UP PROBES on the MAIN MENU doing so will clear the data lists. Select COLLECT DATA from the MAIN MENU. Select MONITOR INPUT from the DATA COLLECTION MENU. Press ENTER to monitor the colorimeter. The absorbance value of the unknown is displayed on the screen of the TI calculator. When the absorbance reading stabilizes, record its value in the space provided in the Data and Calculations table (round to the nearest 0.001). Press + to quit MONITOR INPUT. 15. Discard the solutions as directed by your teacher. Proceed directly to Processing the Data. PROCESSING THE DATA 3

12 1. To determine the iron concentration of your sample, you can use your TI calculator and interpolate along the regression line on your Beer s law curve. Use the following method to convert the absorbance value of the unknown to concentration, in mg/l. Select FIT CURVE from the MAIN MENU. Select LINEAR L 1, L2. To display the linear-regression curve on the graph of absorbance vs. concentration, press ENTER, then select SCALE FROM 0 from the SCALE DATA menu. To interpolate along the regression line, press once. Move the cursor left or right along the regression line. A cursor is displayed on the regression line, along with its X and Y coordinates below the graph. Move the cursor to an absorbance value (Y value) that is equal or nearly equal to the absorbance reading of your unknown sample. Record the absorbance and the concentration of the sample in your data table.. 2. Determine the mass of iron in your sample: The sample solution in Step 13 was made by diluting 5.0 ml of the original liquid vitamin to a100-ml solution and then taking 2 ml of this solution into your test tube and diluting to 10 ml for measuring the concentration in mg/l. Your instructor will explain how to carry out these calculations After you have done your calculations, check the label on the vitamin bottle and compare your result what is on the label. DATA AND CALCULATIONS Test Tube Number Concentration (mg/l) Absorbance Sample solution Iron concentration in the sample solution mg/l 4

13 INTRODUCTION Nitrate The tests described here are used to measure the concentration of nitrate ions, NO 3, in a water sample. The concentration of nitrate will be expressed throughout this section in units of mg/l NO 3 -N. The unit, NO 3 - N, means simply nitrogen that is in the form of nitrate. Nitrate ions found in freshwater samples result from a variety of natural and manmade sources. Nitrates are an important source of nitrogen necessary for plants and animals to synthesize amino acids and proteins. Most nitrogen on earth is found in the atmosphere in the form of nitrogen gas, N 2. Through a process called the nitrogen cycle, nitrogen gas is changed into forms that are useable by plants and animals. These conversions include industrial production of fertilizers, as well as natural processes, such as legume-plant nitrogen fixation, plant and animal decomposition, and animal waste. Sources of Nitrate Ions Agriculture runoff Urban runoff Animal feedlots and barnyards Municipal and industrial wastewater Automobile and industrial emissions Decomposition of plants and animals Although nitrate levels in freshwater are usually less than 1 mg/l, manmade sources of nitrate may elevate levels above 3 mg/l. These sources include animal feedlots, runoff from fertilized fields, or treated municipal wastewater being returned to streams. Levels above 10 mg/l in drinking water can cause a potentially fatal disease in infants called methemoglobinemia, or Blue-Baby Syndrome. In this disease, nitrate converts hemoglobin into a form that can no longer transport oxygen. High nitrate concentrations also contribute to a condition in lakes and ponds called eutrophication, the excessive growth of aquatic plants and algae. Unpleasant odor and taste of water, as well as reduced clarity, often accompany this process. Eventually, dead biomass accumulates in the bottom of the lake, where it decays and compounds the problem by recycling nutrients. If other necessary nutrients are present, algal blooms can occur in a lake with as little as 0.50 mg/l NO 3 -N. Nitrate pollution of surface and groundwater has become a major ecological problem in some agricultural areas. Although fertilizer in runoff is most often blamed, there is evidence that concentration of livestock in feedlots is now the major source of agricultural nitrate pollution. Runoff from fertilized fields is still a significant source of nitrate, although fertilizer use peaked in 1981 and has remained fairly constant since. Expected Levels The nitrate level in freshwater is usually found in the range of 0.1 to 4 mg/l NO 3 -N. Unpolluted waters generally have nitrate levels below 1 mg/l. The effluent of some sewage treatment plants may have levels in excess of 20 mg/l. In a study based on 344 USGS sites throughout the United States, 1 80% of the sites reported nitrate levels less than 1 mg/l, 16% were in the range of 1 3 mg/l, and 4% were greater than 3 mg/l. The percentage of 1 U.S. Geological Survey, National Water Summary , Hydrologic Events and Stream Water Quality, Water- Supply Paper 2400, United States Government Printing Office, 1993,

14 various land types reporting greater than 1 mg/l of nitrate were range land <5%, forested land ~10%, urban areas ~30%, and agricultural land ~40%. Table 1: Nitrate Concentration in Selected Sites Site Nitrate spring level (mg/l NO3 -N) Nitrate fall level (mg/l NO3 -N) Mississippi River, Clinton, IA Mississippi River, Memphis, TN Rio Grande River, El Paso, TX Ohio River, Benwood, WV Willamette River, Portland, OR Missouri River, Garrison Dam, ND Hudson River, Poughkeepsie, NY Platte River, Sharpes Station, MO Summary of Methods A Vernier Nitrate Ion-Selective Electrode (ISE) is used to measure the nitrate-ion concentration in the water, in mg/l NO 3 -N, either on site or after returning to the lab. Materials Checklist CBL System TI Graphing Calculator CHEMBIO program Vernier adapter cable Vernier ISE Amplifier Nitrate Ion-Selective Electrode calculator-to-cbl link cable Low Standard (1 mg/l NO 3 -N) High Standard (100 mg/l NO 3 -N) distilled water tissues small paper or plastic cup (optional)

15 Advanced Preparation The Vernier Nitrate Ion-Selective Electrode (ISE) must be soaked in the Nitrate High Standard solution (included with the ISE) for approximately 30 minutes. Important: Make sure the electrode is not resting on the bottom of the container, and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the electrode. Collection and Storage of Samples 1. This test can be conducted on site or in the lab. 2. It is important to obtain the water sample from below the surface of the water and as far away from shore as is safe. If suitable areas of the stream appear to be unreachable, samplers consisting of a rod and container can be constructed for collection. 3. If the testing cannot be conducted within a few hours, store samples in an ice chest or refrigerator. Testing Procedure 1. Prepare the Nitrate Ion-Selective Electrode (ISE) for data collection. a. The ISE should be soaking in the High Standard. Make sure that it is not resting on the bottom of the container, and that the small white reference contacts are immersed. b. Plug the ISE Amplifier into the adapter cable in Channel 1 of the CBL System. Connect the Nitrate ISE to the ISE Amplifier. c. Connect the CBL System to the TI Graphing Calculator using the link cable. Firmly press in the cable ends. 2. Turn on the CBL unit and the calculator. Start the CHEMBIO program and proceed to the MAIN MENU. 3. Set up the calculator and CBL for the Nitrate ISE. a. Select SET UP PROBES from the MAIN MENU. b. Enter 1 as the number of probes. c. Select ION SELECTIVE from the SELECT PROBE menu. (This will require selecting MORE PROBES several times.) d. Select NITRATE ISE from the SELECT PROBE menu. e. Enter 1 as the channel number. 4. Calibrate the CBL and the Nitrate ISE. To do this, select PERFORM NEW from the CALIBRATION menu. Follow the directions on the calculator screen to allow the system to warm up, then press ENTER. First Calibration Point a. Make sure the voltage reading on the CBL is stable and press TRIGGER on the CBL. b. Enter 100 (the concentration of the standard) on the calculator. Second Calibration Point c. Rinse the ISE thoroughly with distilled water and gently blot it dry with a tissue. Be very gentle when blotting the membrane. Important: Failure to carefully rinse and dry the ISE will contaminate the standard. d. Place the tip of the ISE into the Low Standard (1 mg/l NO 3 -N). Be sure that the ISE is not resting on the bottom of the bottle and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the ISE.

16 e. After briefly swirling the solution, hold the ISE still and wait approximately 30 seconds for the voltage reading displayed on the CBL screen to stabilize. Press TRIGGER on the CBL. f. Enter 1 (the concentration of the standard) on the calculator. g. Press ENTER to return to the MAIN MENU. 5. Set up the calculator and CBL for data collection. a. Select COLLECT DATA from the MAIN MENU. b. Select MONITOR INPUT from the DATA COLLECTION menu 6. To collect the nitrate concentration data: a. Rinse the ISE with distilled water and gently blot it dry with a tissue. b. Pour the water to be tested into the vial provided (or test tube) and place the ISE into the vial/test tube with the sample. Make sure the small white reference contacts are immersed, and that the ISE is not resting on the bottom of the cup. Be sure no air bubbles are trapped below the ISE. c. After briefly swirling the solution, hold the ISE still and wait for the voltage reading displayed on the CBL screen to stabilize. d. Write down the number displayed on the calculator screen as mg Ca 2+ /L e. Take out the probe, rinse with deionized water, gently blot it dry and place it in the next solution to be measured. After the reading stabilizes, write the number on the calculator as mg Ca 2+ /L. f. Clean the electrode as before. g. Press ENTER, then select NO to return to the MAIN MENU. h. Proceed to the next station. DATA & CALCULATIONS Sample Nitrate (mg/l) Hopeland Gardens Tap Water

17 Chloride and Salinity INTRODUCTION Chloride Chloride, in the form of the Cl ion, is one of the major inorganic anions, or negative ions, in saltwater and freshwater. It originates from the dissociation of salts, such as sodium chloride or calcium chloride, in water. NaCl(s) Na + (aq) + Cl (aq) CaCl 2 (s) Ca 2+ (aq) + 2 Cl (aq) These salts, and their resulting chloride ions, originate from natural minerals, saltwater intrusion into estuaries, and industrial pollution. There are many possible sources of manmade salts that may contribute to elevated chloride readings. Sodium chloride and calcium chloride, used to salt roads, contribute to elevated chloride levels in streams. Chlorinated drinking water and sodiumchloride water softeners often increase chloride levels in wastewater of a community. In drinking water, the salty taste produced by chloride depends upon the concentration of the chloride ion. Water containing 250 mg/l of chloride may have a detectable salty taste if the chloride came from sodium chloride. The recommended maximum level of chloride in U.S. drinking water is 250 mg/l. Sources of Chloride Ions River streambeds with salt-containing minerals Runoff from salted roads Irrigation water returned to streams Mixing of seawater with freshwater Chlorinated drinking water Water softener regeneration Salinity Salinity is the total of all non-carbonate salts dissolved in water, usually expressed in parts per thousand (1 ppt = 1000 mg/l). Unlike chloride (Cl ) concentration, you can think of salinity as a measure of the total salt concentration, comprised mostly of Na + and Cl ions. Even though there are smaller quantities of other ions in seawater (e.g., K +, Mg 2+, or SO 2 4 ), sodium and chloride ions represent about 91% of all seawater ions. Salinity is an important measurement in seawater or in estuaries where freshwater from rivers and streams mixes with salty ocean water. The salinity level in seawater is fairly constant, at about 35 ppt (35,000 mg/l), while brackish estuaries may have salinity levels between 1 and 10 ppt. Since most anions in seawater or brackish water are chloride ions, salinity can be determined from chloride concentration. The following formula is used: salinity (ppt) = Cl (mg/l) A Chloride Ion-Selective Electrode can be used to determine the chloride concentration, which is converted to a salinity value using the above formula. Salinity can also be measured in freshwater. Compared to seawater or brackish water, freshwater has much lower levels of salt ions such as Na + and Cl ; in fact, these ions are often lower in concentration than hard-water ions such calcium (Ca 2+ ) and bicarbonate (HCO 3 ). Because

18 salinity readings in freshwater will be significantly lower than in seawater or brackish water, readings are often expressed in mg/l instead of ppt (1 ppt = 1000 mg/l). Increased salinity levels have been observed in the lower reaches of the Colorado and Rio Grande rivers, due to return of irrigation water (see Table 1). In these arid regions of the United States, water readily evaporates during irrigation, resulting in high concentrations of salt ions in the water returned to the rivers. Salinity is also of interest in bodies of water where seawater mixes with freshwater, since aquatic organisms have varying abilities to survive and thrive at different salinity levels. Saltwater organisms survive in salinity levels up to 40 ppt, yet many freshwater organisms cannot live in salinity levels above 1 ppt. Expected Levels Seawater has a chloride ion concentration of about 19,400 mg/l (a salinity of 35.0 ppt). Brackish water in tidal estuaries may have chloride levels between 500 and 5,000 mg/l (salinity of 1 to 10 ppt). Even freshwater streams and lakes have a significant chloride level that can range from 1 to 250 mg/l (salinity of to 0.5 ppt). Table 1: Chloride and Salinity in Selected Sites Site (fall season) Chloride (mg/l) Salinity (mg/l) Salinity (ppt) Columbia River, Newport, WA Mississippi River, Memphis, TN Rio Grande River, San Marcial, NM Rio Grande River, Brownsville, TX Colorado River, State Line, CO-UT Colorado River, Andrade, CA Chloride Concentration and Salinity (ISE) A Vernier Chloride Ion-Selective Electrode is used to measure the chloride ion concentration in the water (in mg/l) either on site or after returning to the lab. Salinity can be determined using the relationship, salinity (ppt) = Cl (mg/l). Materials Checklist CBL System Low Standard (10 mg/l Cl ) TI Graphing Calculator High Standard (1000 mg/l Cl ) CHEMBIO program Very High Standard (20,000 mg/l Cl ) Vernier adapter cable distilled water Vernier ISE Amplifier tissues Chloride Ion-Selective Electrode small paper or plastic cup (optional) calculator-to-cbl link cable

19 Advanced Preparation The Vernier Chloride Ion-Selective Electrode (ISE) must be soaked in the Chloride High Standard solution (included with the ISE) for approximately 30 minutes. Important: Make sure the electrode is not resting on the bottom, and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the electrode. If the electrode needs to be transported to the field during the soaking process, use the ISE soaking bottle. Remove the cap from the ISE soaking bottle and fill the bottle ¾ full with High Standard. Slide the cap onto the electrode, insert it into the bottle, and tighten. Important: Do not leave the electrode soaking for more than 24 hours. Long-term storage should be in a dry environment. Collection and Storage of Samples 1. This test can be conducted on site or in the lab. A 100-mL water sample is required. 2. It is important to obtain the water sample from below the surface of the water and as far away from shore as is safe. If suitable areas of the stream appear to be unreachable, samplers consisting of a rod and container can be constructed for collection. Refer to page Intro-2 of the Introduction of this book for more details. Testing Procedure 1. Prepare the Chloride Ion-Selective Electrode for data collection. a. The ISE should be soaking in the High Standard. Make sure that it is not resting on the bottom of the container, and that the small white reference contacts are immersed. b. Plug the ISE Amplifier into the adapter cable in Channel 1 of the CBL System. Connect the Chloride ISE to the ISE Amplifier. c. Connect the CBL System to the TI Graphing Calculator using the link cable. Firmly press in the cable ends. 2. Turn on the CBL unit and the calculator. Start the CHEMBIO program and proceed to the MAIN MENU. 3. Set up the calculator and CBL for the Chloride ISE. a. Select SET UP PROBES from the MAIN MENU. b. Enter 1 as the number of probes. c. Select ION SELECTIVE from the SELECT PROBE menu. (This will require selecting MORE PROBES several times.) d. Select CHLORIDE ISE from the SELECT PROBE menu. e. Enter 1 as the channel number. 4. Calibrate the CBL and Chloride ISE in units of mg/l Cl. To do this, select PERFORM NEW from the CALIBRATION menu. Follow the directions on the calculator screen to allow the system to warm up, then press ENTER.

20 First Calibration Point a. Make sure the voltage reading on the CBL is stable and press TRIGGER on the CBL. b. Enter 1000 (the concentration of the standard) on the calculator. Second Calibration Point c. Rinse the electrode thoroughly with distilled water and gently blot it dry with a tissue. Be very gentle when blotting the membrane. Important: Failure to carefully rinse and dry the electrode will contaminate the standard. d. If you are testing a freshwater sample, place the tip of the electrode into the Low Standard (10 mg/l Cl ). Be sure that the electrode is not resting on the bottom of the bottle and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the electrode. e. After briefly swirling the solution, hold the ISE still and wait approximately 30 seconds for the voltage reading displayed on the CBL screen to stabilize. Press TRIGGER on the CBL. f. Enter 10. g. Press ENTER to return to the MAIN MENU. 5. Set up the calculator and CBL for data collection. a. Select COLLECT DATA from the MAIN MENU. b. Select MONITOR INPUT from the DATA COLLECTION menu 6. To collect chloride concentration data in MONITOR INPUT mode: a. Rinse the electrode with distilled water and gently blot it dry with a tissue. b. Place the tip of the electrode into the container (bottle or test tube) with sample water. Make sure the small white reference contact is immersed, and that the electrode is not resting on the bottom of the container. Be sure no air bubbles are trapped below the electrode. c. After briefly swirling the solution, hold the ISE still and wait until the voltage reading displayed on the CBL screen to stabilize. d. Record this value on the Data & Calculations sheet (round to the nearest 0.1 mg/l). Note: The sensor does not read values accurately below 1.8 mg/l. If the reading is less than 1.8, write <1.8 mg/l on the Data & Calculations sheet. e. Remove the ISE from the solution, rinse with deionized water, pat dry gently and place it in the next test solution. After the reading has stabilized record the number shown on the calculator on the data sheet. Clean the electrode as before. f. Press ENTER, then select NO to return to the MAIN MENU. g. Go to the next station 7. Determine the salinity value of your sample (in ppt). Use this formula to calculate the salinity, based on the chloride concentration, Cl salinity (ppt) = Cl (mg/l) Record this value in the Data & Calculations table.

21 DATA & CALCULATIONS Column A B Reading Chloride (mg/l Cl ) Salinity (ppt) Hopeland Gardens Tap Water Column Procedure: A. Record the chloride concentration value (in mg/l Cl ) from the calculator. B. Calculate salinity, using the formula: salinity (ppt) = Cl (mg/l). Test Completed: Date: How the Conductivity Probe Works The Vernier Conductivity Probe measures the ability of a solution to conduct an electric current between two graphite electrodes. In water samples, the current flows by movement of dissolved ions. An increasing concentration of ions in the solution results in a greater current flow. The resulting voltage is read by the CBL System and converted to a salinity value (in ppt).

22 INTRODUCTION Calcium and Water Hardness Calcium, Ca 2+ Calcium, in the form of the Ca 2+ ion, is one of the major inorganic cations, or positive ions, in saltwater and freshwater. It can originate from the dissociation of salts, such as calcium chloride or calcium sulfate, in water. CaCl 2 (s) Ca 2+ (aq) + 2 Cl (aq) CaSO 4 (s) Ca 2+ (aq) + SO 2 4 (aq) Most calcium in surface water comes from streams flowing over limestone, CaCO 3, gypsum, CaSO 4 2H 2 O, Sources of Calcium Ions and other calcium-containing rocks and minerals. Groundwater and underground aquifers leach even higher Limestone: CaCO 3 concentrations of calcium ions from rocks and soil. Dolomite: CaCO Calcium carbonate is relatively insoluble in water, but 3 MgCO 3 dissolves more readily in water containing significant Gypsum: CaSO levels of dissolved carbon dioxide H 2 O The concentration of calcium ions (Ca 2+ ) in freshwater is found in a range of 0 to 100 mg/l, and usually has the highest concentration of any freshwater cation. A level of 50 mg/l is recommended as the upper limit for drinking water. High levels are not considered a health concern; however, levels above 50 mg/l can be problematic due to formation of excess calcium carbonate deposits in plumbing or in decreased cleansing action of soaps. If the calcium-ion concentration in freshwater drops below 5 mg/l, it can support only sparse plant and animal life, a condition known as oligotrophic. Typical seawater contains Ca 2+ levels of about 400 mg/l. Calcium Hardness as CaCO 3 When water passes through or over mineral deposits such as limestone, the levels of Ca 2+, Mg 2+, and HCO 3 ions present in the water greatly increase and cause the water to be classified as hard water. This term Calcium Hardness as CaCO 3 results from the fact that calcium or magnesium ions in (mg/l) water combine with soap molecules, forming a sticky Soft: 0-20 scum that interferes with soap action and makes it hard to get suds. One of the most obvious signs of water Moderately soft: hardness is a layer of white film left on the surface of Moderately hard: showers. Since most hard-water ions originate from calcium carbonate, levels of water hardness are often Hard: referred to in terms of hardness as CaCO 3. For example, if a water sample is found to have a Ca 2+ concentration of Very hard: > mg/l, then its calcium hardness as CaCO 3 can be calculated using the formula 2 (30 mg/l Ca 2+ ) (100 g CaCO 3 / 40 g Ca 2+ ) = 75 mg/l calcium hardness as CaCO The reaction occurring with limestone is: CaCO3(s) + CO2(aq) + H2O(l) Ca 2+ (aq) + 2HCO3 (aq). This formula takes into account that the molar mass of Ca is 40 g/mol, and of CaCO3 is 100 g/mol.

23 Note that 30 mg/l Ca 2+ and 75 mg/l calcium hardness as CaCO 3 are equivalent they are simply two different ways of expressing calcium levels. The value of calcium hardness as CaCO 3 can always be obtained by multiplying the Ca 2+ concentration by a factor of 100/40, or 2.5. Another common measurement of water hardness is known as total hardness as CaCO 3. This measurement takes into account both Ca 2+ and Mg 2+ ions. On average, magnesium hardness represents about 1/3 of total hardness and calcium hardness about 2/3. If you are comparing your own test results of calcium hardness as CaCO 3 with results in publications that use units of total hardness as CaCO 3, you can estimate total hardness by multiplying the calcium hardness by 1.5. Expected Levels The concentration of calcium ions (Ca 2+ ) in freshwater is found in a range of 4 to 100 mg/l ( mg/l of calcium hardness as CaCO 3 ). Seawater contains calcium levels of 400 mg/l Ca 2+ (1000 mg/l of calcium hardness as CaCO 3 ). Table 1: Calcium, Calcium Hardness, and Total Hardness in Selected Sites Site (fall season) Calcium (mg/l Ca 2+ ) Ca hardness (mg/l as CaCO3) Total hardness (mg/l as CaCO3) Merrimack River, Lowell, NH Mississippi River, Memphis, TN Rio Grande River, El Paso, TX Ohio River, Grand Chain, OH Willamette River, Portland, OR Missouri River, Garrison Dam, ND Sacramento River, Keswick, CA Hudson River, Poughkeepsie, NY Platte River, Louisville, NE Colorado River, Andrade, CA Summary of Method A Vernier Calcium Ion-Selective Electrode (ISE) is used to measure the calcium ion concentration in the water, in mg/l as Ca 2+, either on site or after returning to the lab. This value is then multiplied by a factor of 2.5 to obtain a value for calcium hardness as CaCO 3, in mg/l. CALCIUM ION-SELECTIVE ELECTRODE MATERIALS CHECKLIST CBL System calculator-to-cbl link cable TI Graphing Calculator Low Standard (10 mg/l Ca 2+ ) Vernier adapter cable High Standard (1000 mg/l Ca 2+

24 Vernier ISE Amplifier tissues Calcium Ion-Selective Electrode small paper or plastic cup (optional) Advanced Preparation The Vernier Calcium Ion-Selective Electrode (ISE) must be soaked in the Calcium High Standard solution (included with the ISE) for approximately 30 minutes. Important: Make sure the ISE is not resting on the bottom, and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the ISE. Testing Procedure 1. Prepare the Calcium Ion-Selective Electrode (ISE) for data collection. a. The ISE should be soaking in the High Standard. Make sure that it is not resting on the bottom of the container, and that the small white reference contacts are immersed. b. Plug the ISE Amplifier into the adapter cable in Channel 1 of the CBL System. Connect the Calcium ISE to the ISE Amplifier. c. Connect the CBL System to the TI Graphing Calculator using the link cable. Firmly press in the cable ends. 2. Turn on the CBL unit and the calculator. Start the CHEMBIO program and proceed to the MAIN MENU. 3. Set up the calculator and CBL for the Calcium ISE. a. Select SET UP PROBES from the MAIN MENU. b. Enter 1 as the number of probes. c. Select ION SELECTIVE from the SELECT PROBE menu. (This will require selecting MORE PROBES several times.) d. Select CALCIUM ISE from the SELECT PROBE menu. e. Enter 1 as the channel number. 4. Calibrate the CBL and Calcium ISE. To do this, select PERFORM NEW from the CALIBRATION menu. Follow the directions on the calculator screen to allow the system to warm up, then press ENTER. First Calibration Point a. Make sure the voltage reading on the CBL is stable and press TRIGGER on the CBL. b. Enter 1000 (the concentration of the standard) on the calculator. Second Calibration Point c. Rinse the ISE thoroughly with distilled water and gently blot it dry with a tissue. Be very gentle when blotting the membrane. Important: Failure to carefully clean and dry the ISE will contaminate the standard. d. Place the tip of the ISE into the Low Standard (10 mg/l Ca 2+ ). Be sure that the ISE is not resting on the bottom of the bottle and that the small white reference contacts are immersed. Make sure no air bubbles are trapped below the ISE. e. After briefly swirling the solution, hold the ISE still and wait approximately 30 seconds for the voltage reading displayed on the CBL screen to stabilize. Press TRIGGER on the CBL. f. Enter 10 (the concentration of the standard) on the calculator. g. Press ENTER to return to the MAIN MENU. 5. Set up the calculator and CBL for data collection. a. Select COLLECT DATA from the MAIN MENU. b. Select MONITOR INPUT from the DATA COLLECTION menu