Dust in the Wind; Chemicals in the Water

Adapted from:

By: Kirstin Bittel & Rachel Hughes

Time: 2-3 Periods
Preparation Time: 15-20 minutes

Station Direction list

Water (of varying temperatures)
Chalk (not dust-free)
Sugar cubes
Steel wool
Blow dryer
White Aquarium Sand
Pieces of granite and sandstone(or other rocks that are not too hard)
Jars and plastic baggies

Students explore mechanical and chemical weathering at stations. Using this information they then design and conduct an experiment to investigate the rate of erosion in different settings.

Purpose – Exploration of different types of weathering and explanation of the difference between types of erosion and erosion in different biomes.

Students will be able to:
1. Articulate some mechanisms of chemical and mechanical weathering through exploration in lab stations in a written statement in their notebooks.
2. Describe how chemical weathering differs from mechanical weathering in a class discussion.
3. Design and conduct an experiment that assesses rates of erosion in two simulated biomes.

National Science Education Standard:
CONTENT STANDARD D – Earth and Space Science
• The earth is a system containing essentially a fixed amount of each stable chemical atom or element. Each element can exist in several different chemical reservoirs. Each element on earth moves among reservoirs in the solid earth, oceans, atmosphere, and organisms as part of geochemical cycles.
• Movement of matter between reservoirs is driven by the earth's internal and external sources of energy. These movements are often accompanied by a change in the physical and chemical properties of the matter. Carbon, for example, occurs in carbonate rocks such as limestone, in the atmosphere as carbon dioxide gas, in water as dissolved carbon dioxide, and in all organisms as complex molecules that control the chemistry of life.
• Interactions among the solid earth, the oceans, the atmosphere, and organisms have resulted in the ongoing evolution of the earth system. We can observe some changes such as earthquakes and volcanic eruptions on a human time scale, but many processes such as mountain building and plate movements take place over hundreds of millions of years.

Teacher Background
Weathering is the process of breaking down large rocks (like mountain ranges) into increasingly smaller bits (sand and silt). There are essentially three types of weathering that dramatically change the surface of the Earth: chemical, mechanical, and biological. Chemical weathering is the process of breaking down rocks by altering them chemically, usually with heat, water, or acids. The resulting particles are often chemically altered and are rounded, often forming clays. Mechanical weathering is the process of breaking down rocks by fracturing or abrasion. The resulting particles are of the same composition and the original rock, and are angular or rounded. Biological weathering is caused by organic materials, like plants and animals. It can result in chemical or mechanical weathering. For example, when a plant root grows into a crack in a rock and splits it apart, it is considered mechanical weathering. However, when a root excretes acid to etch the rock so that it may better attach to the rock, it is considered chemical weathering.

Related and Resource Websites

Rates of Weathering Lab

Weathering Experiments: Sugar Cubes, Steel Wool and Gravel!!!

Prior to class, set up stations as listed on the Stations Direction list handout.

Day One
1. Place a pebble or a pile of sand on your desk or the students’ desks. Ask students “Who has ever been to a beach? Was it sandy or pebbly? Where does that sand or pebble come from?” Most likely students will respond that the pebbles and sand are the result of a larger rock breaking apart. If more appropriate pick a local example of weathering.

2. “Why or how do rocks break down?” Students may focus on factors associated with mechanical weathering; push them to think of other forms of weathering. Write down all variables identified.

3. Can students distinguish mechanical, chemical and biological weathering? As a class, divide the factors into groups. Have students identify how the factors differ once mechanical, chemical and biological weathering has been identified. Have students brainstorm variables that might affect each type of weathering. Record these ideas on the board.

4. Divide the class into groups, Tell students that, for the sake of time, they will exclude biological weathering as it encompasses both chemical and mechanical weathering. At each station they should follow the directions and determine whether it is chemical or mechanical weathering that is being demonstrated. Students should also provide a justification for their choice in their notebooks. They should describe the action and why it is chemical or mechanical weathering.

5. One all groups have rotated around the stations take this opportunity to check that they are able to distinguish between chemical and mechanical weathering. Discuss with the class which is chemical or mechanical at each station.

6. After the chemical and mechanical erosion station rotation ask students what are some of the factors that might change the rate of erosion in different biomes. Students have studied biomes a little in World Geography so they should be familiar with differing environments. List on the board the variables that they come up with. Differing temperatures and moisture levels will probably come up straight away. Students might also come up with different forces and temperatures of wind. Also establish that in some areas rocks might be different sizes.

7. Set students the following challenge: ”In your groups design an experiment which investigates different rates of one type of erosion in two different biomes. For example, how do the rates of chemical erosion on a specific type of rock differ in cold dry environments like the tundra as compared with a hot dry desert?” (Explain that in this activity you are trying to ‘model’ a situation) They are to use the materials available in the class (see the list above.)Students may well pick two situations which require that they manipulate multiple variants. Encourage students who are capable of this to isolate each variable as well as testing as a whole. For some students it is best to focus on just one variable.

8. When planning their experiment students should develop an “if”…”then” hypothesis based upon their earlier observations. If they have multiple variants they should develop multiple “if”…then” statements. They should create a data collection instrument that addresses the “if….then” statements and a protocol to test each one. Let them work on this for the remainder of class. They should be ready to work on this tomorrow.

Day Two
9. Before students proceed with their initial tests, groups should get approval for their experimental design and data collection sheet.
10. Allow students the rest of the day to complete their experiment.
11. Assign Homework – meet with your group to prepare a brief presentation sharing what you have found.

Day Three
12. Have students meet for a few minutes to finalize their presentations.
13. Have groups present their protocols (methods) and results.
14. As groups are presenting, the students in the audience need to record data from the other groups. Each student should be able to describe the general results for each of the other groups in their science notebook. How were the results different than theirs? The same? Why? Be sure to have students do more than just say that different results for different types of weathering are due to that fact alone.

Make sure that you leave enough time for this piece, as it is important. Remind students that they have been studying biomes in Social Studies. Ask the students in what type of biome might they see each type of weathering. Why? In a rain forest, there would be some chemical erosion due to rain dissolving the chemicals that make up the rocks, etc.)

Embedded Assessment
Can students identify the ways in which chemical and mechanical weatherings differ?
This is another opportunity to have students complete a formal laboratory report. An example of how to guide students in this can be found at: http://www.wilson.wnyric.org/t/drobison/labshare/davidrobison/weathering.pdf

Embedded Assessment






























PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

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Last update: November 10, 2009
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