Introductory Concepts in Soil Chemistry
Summary
Students will collect data and display that data using Microsoft Excel. The data will graphically illustrate the relationship between mass and volume in determining density. Based on density, students will seek to determine a relationship between density and soil water holding capacity.
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Learning Goals
Objectives:
· Students will know the relationship of mass and volume in determining density in chemistry.
· Students will demonstrate adequate skills in designing data tables and graphs.
· Students will use statistical analysis for interpreting the significance of data.
Terms:
· Density
· Probability
· Null Hypothesis
· Chi Square
· Students will know the relationship of mass and volume in determining density in chemistry.
· Students will demonstrate adequate skills in designing data tables and graphs.
· Students will use statistical analysis for interpreting the significance of data.
Terms:
· Density
· Probability
· Null Hypothesis
· Chi Square
Context for Use
This is an introductory lab activity for high school Environmental Science students. Students should be reinforcing their understanding of density, data tables, and graphs. Statistical analysis using chi-square tests should be a new, unfamiliar concept to students. This activity takes place early in the course, as the concepts will be continually referred to in future lessons. It should be easy to adapt this to any classroom that has access to soil samples, balances, graduated cylinders, and computer access to Microsoft Excel (or some other spreadsheet/graphing program).
Description and Teaching Materials
Introduction:
What relationship exists between soil density and water holding capacity? This is the guiding question for this activity. Students will work to find the bulk density of a soil sample. Each lab group will be working with the same soil sample, so group data can be compared for accuracy and a discussion on human error. Using a given volume of soil, they will determine its mass, recording their findings on a data table. A number of other samples will be measured (greater volumes) and massed out. Using a scatter plot and trend line slope, students will determine the soil's bulk density.
Using some more of the soil, students will determine its water carrying capacity. Upon completion of that, each lab group will get another "unknown" sample (several different densities), which they must determine its bulk density and water carrying capacity. Pooling our data from the various groups, we'll look for a graphic relationship between density and water holding capacity.
We'll finish by introducing the chi-square test for significance, to determine if any trends we noticed were statistically significant.
Materials:
· 100-200 grams of soil for each lab group (sample A all the same for each group)
· Soil sample B (100-200 grams), using varying densities for each group
· Paper or cookie sheet for spreading out soil samples on counters (enough for all samples)
· Mortar & pestle
· Balance
· 2- 150-200 mL beakers per group
· distilled water (200 mL per group)
· Graduated cylinder (10, 25, 50, or 100 mL will work)
· Time in advance for soil to dry out (varies depending on initial soil moisture, fan help, or heat sources available)
· Scoopula or spoon
· Shovel & freezer bags (for collecting soil)-instructor
Methods:
1. Teacher should collect samples based on the number of lab groups. To take a sample, cut out a roughly 6" by 6" square through the sod layer. Scoop out the sod, to be replaced into the site after sampling. In the square, dig from the edge of your square down about 6 inches, angling toward the center of your square. Do this on the opposite side of the sampling square, so that the sod free sample you've dug out is shaped like the top of a paper milk carton. Cut a slice (about 2 cm thick) on one of the angled sides to be placed in your freezer bag. *Note, the technique itself isn't as critical as sampler being consistent in procedure, especially concerning depth.
2. Each lab group should get a sample A, coming from the same sampling area. The teacher will then have to determine different soil sampling sites that would offer a variety of soil densities. Each lab group needs a sample B, which should vary in density from group to group.
3. Upon getting samples, set soil samples out on flat sheets of paper, tin foil, or flat baking pans. Be sure different samples get clearly marked in advance. Allow them to dry thoroughly.
4. When soil is dry, students can begin their density determination.
5. Have students get a mortar & pestle, and 100-200 grams of sample A soil (perhaps pre-separated by teacher).
6. Students should begin using the mortar & pestle, to break up soil clumps, so it becomes as fine as they can get it, pulling out organic matter that they notice.
7. Using a graduated cylinder, have them measure out 10 mL of soil & then record its mass. They should do this for 20, 30, 40, and 50 mL of soil as well, recording the new mass each time.
8. Using Microsoft Excel, students should type in their data and use the chart wizard to develop a scatter plot. Table and graphing formats will vary among teachers. Students should be able to determine the density of the soil using the slope of the trendline on their scatter plot.
9. Group data can be collectively shared, leading into a discussion on human error (especially if some groups were way off).
10. Each group should have a second (B) soil sample to determine density (procedures as above).
11. Knowing the soil density of A & B, students should then work on determining the water holding capacity of their soil.
12. Each sample should be finely ground (mortar & pestle).
13. Measure out 100 mL of each sample and put into a clean beaker of appropriate size.
14. Measure out 100 mL of water in a graduated cylinder.
15. Little by little, add water to the soil in the beakers. Do this until the soil no longer absorbs the water & it begins pooling on top. Note how much water is left in the cylinder and subtract to find out how many mL are in 100 mL of soil.
16. Group data for soil density should be displayed on a classroom data table (whiteboard) going smallest to largest. Then, as water holding capacity is determined, have students add their findings.
17. Each group should determine a method for graphing the class data, looking at density and water holding capacity.
18. Teacher can then decide to use a chi-square test on the data, to determine if there is a significant difference between these sample sites & their water holding capacity.
What relationship exists between soil density and water holding capacity? This is the guiding question for this activity. Students will work to find the bulk density of a soil sample. Each lab group will be working with the same soil sample, so group data can be compared for accuracy and a discussion on human error. Using a given volume of soil, they will determine its mass, recording their findings on a data table. A number of other samples will be measured (greater volumes) and massed out. Using a scatter plot and trend line slope, students will determine the soil's bulk density.
Using some more of the soil, students will determine its water carrying capacity. Upon completion of that, each lab group will get another "unknown" sample (several different densities), which they must determine its bulk density and water carrying capacity. Pooling our data from the various groups, we'll look for a graphic relationship between density and water holding capacity.
We'll finish by introducing the chi-square test for significance, to determine if any trends we noticed were statistically significant.
Materials:
· 100-200 grams of soil for each lab group (sample A all the same for each group)
· Soil sample B (100-200 grams), using varying densities for each group
· Paper or cookie sheet for spreading out soil samples on counters (enough for all samples)
· Mortar & pestle
· Balance
· 2- 150-200 mL beakers per group
· distilled water (200 mL per group)
· Graduated cylinder (10, 25, 50, or 100 mL will work)
· Time in advance for soil to dry out (varies depending on initial soil moisture, fan help, or heat sources available)
· Scoopula or spoon
· Shovel & freezer bags (for collecting soil)-instructor
Methods:
1. Teacher should collect samples based on the number of lab groups. To take a sample, cut out a roughly 6" by 6" square through the sod layer. Scoop out the sod, to be replaced into the site after sampling. In the square, dig from the edge of your square down about 6 inches, angling toward the center of your square. Do this on the opposite side of the sampling square, so that the sod free sample you've dug out is shaped like the top of a paper milk carton. Cut a slice (about 2 cm thick) on one of the angled sides to be placed in your freezer bag. *Note, the technique itself isn't as critical as sampler being consistent in procedure, especially concerning depth.
2. Each lab group should get a sample A, coming from the same sampling area. The teacher will then have to determine different soil sampling sites that would offer a variety of soil densities. Each lab group needs a sample B, which should vary in density from group to group.
3. Upon getting samples, set soil samples out on flat sheets of paper, tin foil, or flat baking pans. Be sure different samples get clearly marked in advance. Allow them to dry thoroughly.
4. When soil is dry, students can begin their density determination.
5. Have students get a mortar & pestle, and 100-200 grams of sample A soil (perhaps pre-separated by teacher).
6. Students should begin using the mortar & pestle, to break up soil clumps, so it becomes as fine as they can get it, pulling out organic matter that they notice.
7. Using a graduated cylinder, have them measure out 10 mL of soil & then record its mass. They should do this for 20, 30, 40, and 50 mL of soil as well, recording the new mass each time.
8. Using Microsoft Excel, students should type in their data and use the chart wizard to develop a scatter plot. Table and graphing formats will vary among teachers. Students should be able to determine the density of the soil using the slope of the trendline on their scatter plot.
9. Group data can be collectively shared, leading into a discussion on human error (especially if some groups were way off).
10. Each group should have a second (B) soil sample to determine density (procedures as above).
11. Knowing the soil density of A & B, students should then work on determining the water holding capacity of their soil.
12. Each sample should be finely ground (mortar & pestle).
13. Measure out 100 mL of each sample and put into a clean beaker of appropriate size.
14. Measure out 100 mL of water in a graduated cylinder.
15. Little by little, add water to the soil in the beakers. Do this until the soil no longer absorbs the water & it begins pooling on top. Note how much water is left in the cylinder and subtract to find out how many mL are in 100 mL of soil.
16. Group data for soil density should be displayed on a classroom data table (whiteboard) going smallest to largest. Then, as water holding capacity is determined, have students add their findings.
17. Each group should determine a method for graphing the class data, looking at density and water holding capacity.
18. Teacher can then decide to use a chi-square test on the data, to determine if there is a significant difference between these sample sites & their water holding capacity.
Teaching Notes and Tips
Assessment
The primary source of assessment will be their science lab notebook, looking for work shown, raw data, and calculations. They should have included the lab procedures in some form, and taped in print versions of data tables & graphs. They will have answered posed questions in their notebook as well, specifically focusing on the initial lab question.
Standards
I.B.1. analyzing data
I.B.3. applying mathematics to analyze data
I.B.3. applying mathematics to analyze data