Teacher Notes
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Teacher Notes![]() Lead in SoilStudent Laboratory KitMaterials Included In Kit
Lead nitrate solution, 0.5 M, 75 mL
Lead nitrate solution, 1 M, 75 mL Sodium rhodizonate, 0.2 g (in a 100-mL bottle) Potting soil, 8 lbs Weighing dishes, large, 3 Additional Materials Required
Water, distilled or deionized*†
Balance, 0.1-g precision* Beakers, 50-mL, 6* Beakers, 500-mL, 3† Filter paper (size to fit funnel), 3* Funnels, polypropylene or borosilicate glass, 3* Funnel support* Graduated cylinder, 50-mL* Graduated cylinders, 100-mL, 3† Marker or wax pencil* Pipet, graduated* Soil, lead-free, 500 g* Stirring rods, 3*† Support stand* Weighing dishes, medium, 3* *for each lab group †for Prelab Preparation Prelab PreparationSeveral days in advance
Safety PrecautionsLead nitrate is moderately toxic by inhalation and ingestion, a body tissue irritant and a possible carcinogen. 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. DisposalPlease 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 waste lead nitrate, filtrate and contaminated soil may be disposed of by a licensed hazardous waste disposal company according to Flinn Suggested Disposal Method #27f. Excess sodium rhodizonate solution may be disposed of down the drain with an excess of water according to Flinn Suggested Disposal Method #26b. Lab Hints
Teacher Tips
Correlation to Next Generation Science Standards (NGSS)†Science & Engineering PracticesAsking questions and defining problemsDeveloping and using models Planning and carrying out investigations Analyzing and interpreting data Engaging in argument from evidence Disciplinary Core IdeasMS-PS1.A: Structure and Properties of MatterMS-LS2.A: Interdependent Relationships in Ecosystems MS-LS2.B: Cycle of Matter and Energy Transfer in Ecosystems MS-ESS3.C: Human Impacts on Earth Systems HS-LS2.A: Interdependent Relationships in Ecosystems HS-LS2.B: Cycle of Matter and Energy Transfer in Ecosystems Crosscutting ConceptsPatternsCause and effect Systems and system models Performance ExpectationsMS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. Answers to Prelab Questions
Sample Data{10927_Data_Table_1}
Answers to Questions
ReferencesEnvironmental Protection Agency website http://www.epa.gov/lead/ (accessed April 2008). Recommended Products
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Student Pages
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Student Pages![]() Lead in SoilIntroductionLead is a naturally-occurring element. It is a heavy, soft, bluish-gray metal. Lead is a stable element; it does not decompose over time. Instead, lead accumulates in the soil and sediment around areas where lead is an airborne particulate byproduct of manufacturing or where deteriorating lead paint settles. Concepts
BackgroundThe processes of life are a series of chemical reactions that occur in the body of the living organism. Living things eat or absorb compounds composed of elements from the environment surrounding them. Many elements are beneficial while other elements can be harmful to the organism. Lead is an example of an element that is harmful to human beings. The body absorbs lead into the bloodstream. From the bloodstream, lead mimics calcium and bioaccumulates in bones where it can slowly leach out into the bloodstream for an entire lifetime. Lead also affects other systems that depend on calcium such as nerves, muscles and kidneys. Lead is able to cross the blood–brain barrier where it causes damage to all areas of the brain. Lead exposure can lead to learning disabilities, behavioral problems, decreased intelligence, as well as speech, language, hearing, and muscle coordination issues (see Figure 1). Children are especially vulnerable to lead poisoning. Children need a lot of calcium for both bone and brain growth. If not enough calcium is available, lead will be absorbed instead. Children tend to absorb larger doses of lead due to both their smaller size and the habit of putting objects or hands into their mouths. Very high doses of lead can cause mental retardation, coma and even death. In adults, lead exposure can cause nerve, muscle and memory problems, increased blood pressure and even fertility problems. {10927_Background_Figure_1}
Lead exposure can come from a work environment or from around the house. Adults who work around lead should be aware of the hazard and take precautions to ensure the lead does not come home with them. Sources of lead around the house are deteriorating lead paint, lead in water or lead in soil around the home. Lead was added to paint to brighten colors and as an additive to provide longevity for the paint. As lead paint deteriorates due to age or abrasion, small particles of paint become airborne before settling as dust over surfaces such as the floor or the soil around the outside of the house. Lead house paint was manufactured until 1978. Also until 1978, lead was added to gasoline to help stop engine knocking and created a more efficient combustion engine. The lead was not consumed in the combustion reaction however. Instead it was expelled as small particles into the atmosphere as part of the exhaust. Precipitation caused the small lead particles, called particulate, to wash off buildings into the soil or storm drains where it ran into streams, rivers and lakes. Due to the persistence of lead, most children have their blood tested for lead before the age of two. If a high level of lead in the blood is discovered, the child will undergo medical treatment and the parents are advised to determine the source of the lead so that the lead exposure can be diminished. If the blood lead levels are high enough the doctor may prescribe treatment to reduce the level of lead in the body as well as changing the diet of the affected individuals. A diet high in calcium, iron, zinc and vitamin C will reduce the amount of lead absorbed by the body. Analytical testing of toys, water, paint and soil all involve acid extraction of lead from the substrate followed by analysis using an analytical instrument such as an atomic absorption spectrophotometer (AA) or an inductively coupled plasma mass spectrometer (ICP-MS). These analytical instruments capitalize on the physical and chemical properties of the lead. Lead becomes soluble at low pH so treatment with acid will leach lead from the non-lead matrix. The analytical instrument converts lead ions into an atomic state where they absorb light at a specific wavelength. The light absorbed by the lead in the unknown samples are compared to the amount of light absorbed by samples with a known amount of lead. These analytical tests are very accurate and the labs that perform the tests are often certified by a national accreditation organization. It would be very expensive to test all areas around a house for lead using laboratory testing. A field screening process is often used to decrease the number of samples that must be sent to the laboratory for analysis. Two common methods are portable X-ray fluorescence (XRF) and rhodizonate testing. A portable lead-testing XRF looks similar to a radar speed detector. The XRF is pressed against a painted surface and the trigger is pulled causing a shielded radioactive source to be exposed. The source excites any lead atoms which are sensed by the detector and a reading appears on the data screen. Lead paint located below several layers of lead-free paint will still yield a positive result. Because it employs a radioactive source, portable XRF instruments may only be used by highly trained individuals. The second screening test for lead is rhodizonate testing. Rhodizonate testing uses a simple colorimetric method. The yellow-orange colored sodium rhodizonate reacts with lead to form a pink complex. The lead testing swabs that are commercially available are often rhodizonate tests. There are limits with rhodizonate screening tests. First, other metals such as cadmium, silver, tin, and barium give a false positive response by also reacting with sodium rhodizonate to form a pink complex. Second, rhodizonate tests are qualitative, not quantitative. Third, the rhodizonate solution degrades quickly; commercial products must be used within a few minutes of mixing. Experiment OverviewThe purpose of this experiment is to determine the presence or absence of lead in a sample of soil using the sodium rhodizonate screening procedure. Materials
Sodium rhodizonate, 0.2%, 3 mL
Water, distilled or deionized Balance, 0.1-g precision Beakers, 50-mL, 6 Filter paper (size to fit funnel), 3 Funnel support Funnels, polypropylene or borosilicate glass, 3 Graduated cylinder, 50-mL Marker or wax pencil Pipet, graduated Soil sample A, 10 g Soil sample B, 10 g Soil sample C, 10 g Stirring rods, 3 Support stand Weighing dishes, medium, 3 Prelab Questions
Safety PrecautionsLead nitrate is moderately toxic by inhalation and ingestion, a body tissue irritant and a possible carcinogen. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines. Procedure
Student Worksheet PDF |