Download Disappearing Rock

Grade Level: Duration: Location: Vocabulary: 6th -8th grades
One 60 minute class period
Classroom or laboratory
Chemical weathering
Disappearing Rock
Introduction:
Limestone is a soft sedimentary rock made of the mineral calcium carbonate. This mineral reacts quickly with
slightly acidic rainwater. This process is referred to as chemical weathering. The chemical reaction for the formation
of acid rain is:
Water + Carbon Dioxide → Carbonic Acid
H2O(l) + CO2(g) → H2CO3(aq)
The same reaction occurs between rain and the carbon dioxide found in soil.
The chemical reaction that occurs to cause the dissolution of limestone is:
Carbonic Acid + Calcium Carbonate → Calcium Oxide + Water + Carbon Dioxide
H2CO3(aq) + CaCO3(s) → CaO + H2O(l) + 2CO2(g)
Metamorphic and igneous rocks are made of harder materials and weather at a much slower rate – over thousands
of years versus just a few years for limestone.
Engage:
After reviewing the rock chart, show the students the rock samples they will be using in the activity. Based on the
rock chart, have the students attempt to classify the rocks. Have the students predict which rocks will react with the
acid. Ask the students how the limestone will affect the pH of water.
Materials for each group:
• Rock Chart
• Rock samples (3-5 of each type of rock)
•Vinegar
• Hand lens
•Dropper
• Bowl deep enough to cover the rock in vinegar
• Science notebook
•Scales
• Hydrion pH test strips
Explore:
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Distribute materials to each group.
Have students observe the rock with the hand lens and compare observations to descriptions on the Rock Chart.
Have students predict the reaction that will occur between their sample and the vinegar.
Using wide Hydrion pH test strips, test the pH of the vinegar.
Place the rock in the bowl and cover with vinegar. Allow to stand for 5 minutes.
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6. Remove the rock from the vinegar solution, rinse, and dry.
7. Check the pH of the used vinegar solution.
8. Repeat steps 2-7 with additional rock samples.
Explain:
1. Have students discuss their observations and conclusions.
2. Which type of rock would be most commonly found in areas with karst landscapes?
3. What happened to the pH of the vinegar solution?
Elaborate:
1. Which type of rock would be the best foundation for a house?
2. Which type of rock would be the best foundation for a lake?
3. Why are there no ponds, creeks, or other bodies of surface water in karst landscapes? (The exception would be
a sinkhole pond that is fed by part of an underground karst stream.)
Evaluate:
1. Develop a model to describe the processes in nature that act together to cause the rock cycle.
KENTUCKY CORE ACADEMIC STANDARDS ALIGNMENT
Mathematics
• 6.RP.A.1: Understand the concepts and use ratio language to describe a ratio relationship between two
quantities.
• 6.SP.B.4: Display numerical data in plots on a number line, including dot plots, histograms, and box plots.
• 7.SP.A.1: Understand that statistics can be used to gain information about a population.
Science
• MS-ESS2-1: Develop a model to describe the cycling of Earth’s materials and the flow of energy
that drives this process.
• MS-ESS2.C: The roles of water in earth’s surface processes.
Language Arts
• SL.8.5: Integrate multimedia and visual displays into presentations to clarify information, strengthen claims
and evidence, and add interest.
Suggested Reading/Resources
• Everything Rocks and Minerals by Steve Tomecek and Carsten Peter
• Sedimentary Rocks by Chris Oxlade
• The Complete Illustrated Guide to Rocks of the World: A Practical Directory of Over 150 Igneous,
Sedimentary and Metamorphic Rocks by John Farndon
• Weathering and Erosion: Wearing Down Rocks (Rock It!) by Steven M. Hoffman
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