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Part E: Nitrates and Phosphates
Overview/Introduction:
Nitrogen and phosphorus are essential elements for all life. Human activity such as rinsing off sidewalks has caused many pollutants to be washed into ground water, flowing water, and bodies of water. Natural activities of organisms can also change the chemistry of these waters. Minerals and organic matter in high quantities can cause aquatic plant populations to proliferate and die. This can populations of consumers, such as fish, to crash due to lack of oxygen.
Purpose or Objective:
- To accurately measure and compare the concentrations of nitrates and phosphates in water samples collected from various zones of a river, stream, pond, or lake.
Time Required: Two periods
Materials, Tools, and Resources Needed: CBL, Graphing calculator or lap top, Colorimeter, Cups or beakers, Pipet pump or bulb, Cuvette, 125 ml Erlenmeyer flask; three 50 ml. Erlenmeyer flasks, two 10 ml pipets or graduated cylinders; 25 ml graduated cylinder, Low standard ( l mg/L NO3), Hight standard (100 mg/L NO3), Distilled water, Phosphate standard, .1 M HCl, PhosVer 3 Phosphate Powder Pillows
Teacher Preparation:
Be sure to have students wear goggles. You might choose to do the nitrate and phosphate tests separately. This would take one period each.
The Nitrate ion-selective electrode must be soaked in the Nitrate High Standard for approximated 30 minutes before use. Do not rest the electrode on the bottom of the container and the white reference contacts are immersed in the water. Make sure no air bubbles are trapped below the electrode. *Do not soak for more than 24 hours.
If samples cannot be tested within a few hours, store in an ice chest or refrigerator.
Concentration of nitrates is measured in mg/L NO3 and concentration of phosphates mg/L PO4.
Procedure:
Measure and record the concentrations of nitrates and phosphates in various zones of a body of water in the field.
- River or Stream: Upper reaches, middle reaches and mouth
- Pond or Lake: Littoral (close to shore) and limnetic (open water) zones at various depths.
- Ocean: Neritic including littoral (intertidal) zone and pelagic (surface).
Collect samples of water from the groups mentioned above as far away from shore as possible and below the surface of the water. Use the water sampler from the first activity. Collect 200 ml of water from each source.
Nitrate Test Procedure for CBL (see CBL manual for complete instructions):
- Connect the electrode while still immersed into the CBL interface. Use the link cable to connect the graphing calculator or lap top to the interface.
- Turn on the calculator or lap top and start the data program.
- Select and calibrate the nitrate electrode.
- Set up the data collection mode.
- Rinse the nitrate electrode with distilled water. Place tip into the sample. Make sure the white reference contacts are immersed and that the electrode is not resting on the bottom and that no air bubbles are trapped below the electrode.
- Swirl the solution, hold the electrode still, and wait 30 seconds.
- Select START to begin sampling; *hold electrode still for 10 seconds.
- The nitrate concentration will appear on the screen after 10 seconds.
Repeat steps 6-9 for additional sites and samples.
RECORD your data on the chart
Phosphate Test Procedure for CBL (see CBL manual for complete instructions):
- Label two Erlenmeyer flasks; measure 25 ml of sample water into each.
- Testing for orthophosphates. Label a third flask with an S for standard and add 25 ml of 10.9 mg/L Phosphate standard.
- Add a Phos Ver 3 Phosphate Pillow to the flask; swirl until the powder dissolves. It will take 2 minutes for the reaction to take place; continue with step 4.
- Connect the colorimeter into the CBL interface. Use the link cable to connect the graphing calculator or lap top to the interface.
- Prepare a blank by filling an empty cuvette 3/4 full of distilled water. Seal with a lid.
- Turn on the calculator or lap top and start the data program.
- Set up the calculator and interface for the colorimeter.
- Place the blank in the cuvette slot and close the lid.
- Calibrate the colorimeter.
- Set up the data collection mode.
- Collect absorbance-concentration data for the blank and the phosphate standard solution. This process will create a standard curve that will be used to determine the phosphate concentrations of the sampes.
- Repeat step 12 with the water samples that have reacted with the powder.
- Determine the concentration of phosphate by interpolating the absorbance value on the standard curve.
Student Handouts/ Record Sheets
- Data chart
Student Discussion Questions:
- Which of your samples has the highest amount of nitrates? Phosphates?
- What do you suppose was the source of the nitrates? Phosphates?
- Algal bloom may occur in fresh water bodies when there is a sudden rise in nitrates and phosphates. What role might temperature play? How will this large population of algae affect the amount of dissolved oxygen in the water? What happens when the algae population begins to die? How does this affect the amount of dissolved oxygen? What may happen to fish and other aquatic organisms?
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Grade 9-12
California Science Content Standards
Acids and Bases
5. Acids, bases, and salts are three classes of compounds that form ions in water solutions. As a basis for understanding this concept:
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Students know the observable properties of acids, bases, and salt solutions. |
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Students know acids are hydrogen-ion-donating and bases are hydrogen-ion-accepting substances. |
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Students know how to use the pH scale to characterize acid and base solutions. |
Solutions
6. Solutions are homogenous mixtures of two or more substances. As a basis for understanding this concept
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Students know the definitions of solute and solvent. |
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Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent compositions |
Ecology
6. Stability in an ecosystem is a balance between competing effects. As a basis for understanding this concept:
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Students know how to analyze changes in an ecosystem resulting from changes in climate, human activity, introduction of nonnative species, or changes in population size. |
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Students know how water, carbon, and nitrogen cycle between abiotic resources and organic matter in the ecoystem and how oxygen cycles through photosynthesis and respiration. |
Investigation and Experimentation
Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and to address the content in the other four strands, students should develop their own questions and perform investigations. Students will:
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select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data. |
National Education Technology Standards for All Students
3. Technology productivity tools
Students use technology tools to enhance learning, increase productivity, and promote creativity.
Technology research tools
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Students use technology to locate, evaluate, and collect information from a variety of sources. |
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Students use technology tools to process data and report results. |
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Students evaluate and select new information resources and technological innovations based on the appropriateness to specific tasks. |
Technology problem-solving and decision-making tools
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Students use technology resources for solving problems and making informed decisions. |
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Students employ technology in the development of strategies for solving problems in the real world.
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The Integrating Technology into Science Instruction webpages project is partially funded by grants from The Boeing Company and The Ralph M. Parsons Foundation. Integrating Technology into Instruction is a project of Target Science (target@laep.org) and is displayed on the Los Angeles Educational Partnership Learning Exchange. Target Science is an initiative of the Los Angeles Educational Partnership.