Materials Included In Kit

Additional Materials Required

Prelab Preparation

The Walker Quarry test samples should be prepared before class. Choose from the three scenarios below and follow the prep-aration instructions for each sample. Each test sample may be placed into a 1000-mL beaker or similar container. Add the sand and/or gravel up to the graduation marks listed below. Mix each sample well with a stirring rod.

Scenario 1: Swimming Pool Chemical Leakage

• Walker Quarry Test Sample 1: sand, 500 mL
• Walker Quarry Test Sample 2: gravel, 250 mL; sand, 250 mL; sodium hypochlorite solution, 1 mL
• Walker Quarry Test Sample 3: gravel, 500 mL; sodium hypochlorite solution, 5 drops

Scenario 2: Acidic Waste from Copper Kettle Co.

• Walker Quarry Test Sample 1: citric acid, 5 g; sand, 500 mL
• Walker Quarry Test Sample 2: citric acid, 5 g; Gravel, 250 mL; sand, 250 mL
• Walker Quarry Test Sample 3: gravel, 500 mL

Scenario 3: Steel Factory waste entering Walker Quarry and acidic waste from the Copper Kettle Co.

• Walker Quarry Test Sample 1: iron(III) sulfate, 2 g; sand, 500 mL
• Walker Quarry Test Sample 2: gravel, 250 mL; iron(III) sulfate, 2 g; sand, 250 mL
• Walker Quarry Test Sample 3: gravel, 500 mL

Safety Precautions

Chlorine DPD #4R TesTabs^® contain chemicals which may irritate skin or be harmful if swallowed. The TesTab reagents used in this kit were designed with safety in mind. The single-use, foil packaged TesTabs are easy to dispense. Store TesTabs in a cool, dry place and only open when ready to use the tablet. A single tablet, either alone or reacted with a sample, is not a health hazard. However, TesTabs should not be ingested. Sodium hypochlorite solution is a corrosive liquid that is moderately toxic by ingestion and inhalation and reacts with acid to evolve chlorine gas. Iron(III) sulfate is slightly toxic by ingestion. Potassium thiocyanate solution is moderately toxic by ingestion and may emit toxic cyanide gas if heated or in contact with concentrated acids. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The test samples may be disposed of according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period.
• Three Color Comparison Charts have been provided for the chlorine test. Divide the Color Comparison Charts among the student groups accordingly.
• The sand and gravel samples originally tested for this activity contained small traces of iron. This will not affect the three scenarios listed in this write-up. Results may vary with different sand and gravel samples.
• TesTabs are a vendor product of the LaMotte Company. SDSs are available through the manufacturer website.

Teacher Tips

• Have students write reports on soil contaminates, their sources and effects. Encourage students to use the Internet to explore the wide range of information available.

• Introduce and discuss real-life examples of pollution. A good example is the water pollution that occurred on the Cuyahoga River. The Cuyahoga (which eventually empties into Lake Erie) is a river that runs through Akron and Cleveland, Ohio. In the 1950s and 60s, chemical and steel factories dumped up to 155 tons a day of toxic chemicals, sludge and solvents into the river. The river was also bombarded with animal manure, pesticides, fertilizers and raw and poorly treated sewage. In 1959, oil slicks from these substances caught fire and burned for a total of eight days. Firefighting measures only complicated the situation. As water was sprayed from the fire hoses the blaze was spread even further. Ten years after this incident the river caught fire once again. These incidents were strong factors leading to the passage of the Clean Water Act in 1972.
• Take a field trip to a water treatment facility. Discuss the pollutants covered in this activity as well as other factors monitored by the treatment facility.
• Here are the reactions that take place for each sample:
  Chlorine: Chlorine DPD #4R TesTabs contain diethyl-p-phenylenediamine (DPD). When chlorine oxidizes DPD, a pink color is obtained. The color intensity is proportional to the chlorine concentration.
  Iron: Fe³⁺(aq) + SCN^–(aq) → Fe(SCN⁾²⁺(aq) Red Complex.
  pH: The rainbow acid indicator is a solution that uses a combination of indicators to obtain a rainbow spectrum of colors for acid solutions having values between 1 and 7.

Sample Data

Scenario 1—Swimming Pool Chemical Leakage

Answers to Questions

1. What pollutant(s) were identified in the test samples?

   Student answers will vary.

2. Who was most likely causing pollution at the Walker Quarry based on the test results gathered from the procedure?

   Student answers will vary.

3. What further testing could be done to determine the culprit?

   Take test samples closer to each company. Look for leakage of chemical near company buildings, etc.

4. What type of pollution most likely occurred—point or non-point pollution?

   Student answers will vary.

5. What adverse effects could occur from the pollution in Walker Quarry?

   High levels of chlorine can be harmful and possibly fatal to organisms. Iron could stain laundry and plumbing fixtures and cause food and water to taste and look peculiar. Soil that is too acidic or basic may be toxic to the roots of plants and nutrient availability to the plants may be altered.

Teacher Handouts

12765_Teacher1.pdf

Introduction

The land in and around the Walker Quarry has become contaminated. How did this happen? Use forensic problem solving skills to solve the problem.

Concepts

• Soil forensics

• pH
• Iron contamination
• Chlorine contamination

Background

Soil is not an easily defined substance. Farmers define soil as the top 6–12 inches of the Earth’s crust where crops are grown. Geologists define soil as the organic and mineral matter composing the Earth. Forensic geologists consider soil as Earth material that has been collected in a particular investigation. All natural and artificial objects on or near the surface of the Earth are considered part of the soil. These might include rocks, minerals, vegetation and other particles. In this activity, gravel and sand particles from the Walker Quarry will be tested to determine levels of chlorine, iron and copper in the soil.

Chlorine is added to municipal water systems and swimming pools as a bactericide. Large levels of chlorine introduced to streams, lakes, rivers and ponds can be harmful and possibly fatal to organisms. Chlorine in most drinking water is maintained under 0.75 parts per million.

Iron, in small amounts, is an essential mineral to human nutrition. It is present in nature from sources such as rocks and soil and is also present due to industrial waste and the corrosion of iron pipes. When the concentration of iron is above 0.1 parts per million, it will precipitate as iron oxide when it comes into contact with air. Iron oxides will stain laundry and plumbing fixtures. It will also cause food and drinks to taste and look peculiar. Iron concentrations in drinking water should not exceed 0.3 parts per million.

The pH test is a standard soil test. pH is a measure of the relative abundance of hydrogen ions in a water sample. In pure water, the hydrogen ion concentration [H⁺] is equal to 1.0 x 10^–7 moles per liter. Equation 1 shows how the pH value of a sample is calculated from the hydrogen ion concentration.

As soil becomes more acidic, the pH values decrease from 7 to 6 to 5 and so on. As the soil becomes more basic, the pH values increase from 7 to 8 to 9, etc. See Figure 1 for examples of everyday substances with different pH levels.

Soil pH ranges are typically between 4 and 8. The pH of soil is dependent upon the interactions between minerals, ions in solution and exchange of cations in the soil. Basic pH readings are found in soil due to the reaction of water, magnesium, calcium and sodium. When water and high amounts of calcium, magnesium or sodium carbonates and oxides are present in soil, hydroxide ions are formed (Equation 2).

Soils with a low pH (acidic soils) on the other hand are caused by the presence of slightly acidic water in soil (acid rain), respiration of organisms in soil, and also by crop production. Acidic water percolates through soil and exchanges the basic ions in soil with hydrogen ions and aluminum ions. This replacement of bases in soil is especially prevalent in humid areas where the amount of rainfall exceeds the natural amount of evaporation. The large amount of precipitation allows for a large amount of leeching of soil to occur.

Soil also becomes acidic during respiration of plant roots and other organisms that are present in soil. When respiration occurs, an excess of carbon dioxide is found in soil. When carbon dioxide (CO₂) reacts with water, carbonic acid (H₂CO₃) is formed. Carbonic acid then decomposes, releasing hydrogen ions into the soil and lowering the soil pH (Equation 3).

The pH of a soil affects both the soil, plants and organisms in the soil. Soil that is too acidic or basic may be toxic to the roots, but these conditions do not normally directly affect plants nearly as much as they affect nutrient availability. For example, in basic soils, minerals, such as copper, iron and manganese, become less available to plants, while acidic soils may inhibit the growth of nitrogen-fixing bacteria.

There are two main ways contaminants enter the soil. They are known as point-specific and nonpoint pollution. Point-specific pollution is contamination that comes from a specific location. An example would be a factory that has a chemical discharge pipe that leads directly to a water source. This type of contamination can be identified and controlled much more readily than nonpoint sources.

Nonpoint pollution does not come from a specific location. Some examples of nonpoint pollution are runoff of water from city areas, agricultural land or from poor forestry practices. This type of contamination occurs when runoff water such as snowmelt or rainfall travels over an area of land. As this water moves over the soil, it picks up or delivers waste and caries it to a body of water. This water will seep down through the soil and eventually reach ground water supplies. This type of pollution can be difficult to pinpoint and eliminate.

Experiment Overview

Recent soil sample studies at the Walker Quarry have shown very high amounts of pollutants. An all-out effort is being made to discover what is causing the pollution in the quarry. It is your job, as the forensic scientist, to determine the possible sources of contamination.

Materials

Safety Precautions

Chlorine DPD #4R TesTabs^® contain chemicals which may irritate skin or be harmful if swallowed. The TesTab reagents used in this kit were designed with safety in mind. The single-use, foil packaged TesTabs are easy to dispense. Store TesTabs in a cool, dry place and only open when ready to use the tablet. A single tablet, either alone or reacted with a sample, is not a health hazard. However, TesTabs should not be ingested. Potassium thiocyanate solution is moderately toxic by ingestion and may emit toxic cyanide gas if heated or in contact with concentrated acids. Wear chemical splash goggles and chemical-resistant gloves. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Three test samples were gathered from the Walker Quarry. See the Walker Quarry Master Map for the locations.
2. Obtain a Walker Quarry test sample container. Record the number of the test sample on the Soil Contamination Worksheet.
3. Place 20 mL of the first sand and/or gravel test sample into a Walker Quarry test sample container.
4. Add 25 mL of distilled water into the Walker Quarry test sample container.
5. Cap and swirl the container for 30 seconds.

Chlorine Test

6. Using a pipet, place 5 mL of the water from the Walker Quarry test sample container into a graduated soil sample tube.
7. Add one Chlorine DPD #4R TesTab to the soil sample tube.
8. Cap the tube and shake until the tablet has dissolved.
9. Wait for five minutes and compare the color of the sample to the Chlorine Color Comparison Chart. Record the amount of chlorine (as parts per million chlorine) on the Soil Contamination Forensics Worksheet.
10. Dispose of the sample according to the instructor and rinse the soil sample tube twice with distilled water. Save for future chlorine tests.

Iron Test

11. Place 5 mL of the water from the Walker Quarry test sample container into a plastic medicine cup.
12. Using a pipet, place 10 drops of 0.5 M potassium thiocyanate into the medicine cup.
13. Swirl and record any color change in the Soil Contamination Forensics Worksheet.
14. The presence of a dark red or orange color change indicates that the amount of iron is over the accepted value.
15. Dispose of the sample according to the instructor and rinse the medicine cup with distilled water. Save for future tests.

pH Test

16. Place 5 mL of the water from the Walker Quarry test sample container into a clean, plastic medicine cup.
17. Obtain and place 5 drops of universal indicator rainbow acid into the plastic medicine cup.
18. Compare the color of the test sample to the universal indicator rainbow acid chart. Record the pH of the test sample in the Soil Contamination Forensics Worksheet.
19. Dispose of the sample according to the instructor and rinse the medicine cup twice with distilled water. Save for future tests.
20. Rinse the Walker Quarry test sample container twice with distilled water.
21. Repeat steps 6–20 twice more using Walker Quarry Samples 2 and 3, respectively.
22. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

12765_Student1.pdf