Grade Level: 3rd – 5th grades
Duration: One 60 minute class period
Location: Classroom or laboratory
Vocabulary: non-clastic sedimentary rock, sinkhole, carbonic acid, chemical change
When any type of precipitation occurs, water droplets combine with gases, such as carbon dioxide, in the air to form a dilute acidic solution. Some rocks are more sensitive to acidic solutions than others. Limestone or calcite
(CaCO3), the most abundant of the non-clastic sedimentary rock types, can be easily dissolved by acids, increasing the likelihood of a sinkhole or other karst formation.
After reviewing the steps of the rock cycle, ask students if they have ever been inside a cave. Have them describe the inside of the cave. Was it damp or dry? What caused the cave to form? What would happen if the cave ceiling collapsed? What would happen to the landscape above the collapsed cave? Explain to students that the surface depression would be called a sinkhole. Explain to students that this activity will involve using chalk, a compound similar to limestone. At one time, chalk was made of natural rock chalk dust and a compound such as starch or gum which held the particles together. Modern chalk sticks are made of other calcium compounds such as calcium silicate or calcium sulfate (better known as Plaster of Paris). If time permits, let students make their own sidewalk chalk for use in this activity.
• Dropper
• Several pieces of different types of chalk
- Dustless chalk
- Pastel chalk
- Sidewalk chalk
• Vinegar (a weak solution of acetic acid that reacts similarly to carbonic acid)
• Water (rainwater preferred, but tap water will also work)
• Tray or saucer
• Hand lens
• Nail or similar item for carving chalk
• Clear container large enough for all the group’s chalk pieces
1. Divide the students into Groups A, B, and C.
2. Give Group A several pieces of dustless chalk, Group B several pieces of pastel chalk, and Group C several pieces of sidewalk chalk.
3. Distribute the remaining materials evenly between the groups.
4. Ask the students to predict what will happen when the water is added to the chalk.
5. Have each group place one piece of chalk on their tray.
6. Fill a dropper with water and slowly add drops of water to the surface of the chalk. Describe any reactions that occur.
7. Once finished, have students share predictions and observations from the chalk test.
8. Repeat steps 3-6 using vinegar instead of water.
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1. Have the students compare their predictions and their observations.
2. Explain to students that the observed reaction is a type of chemical change similar to chemical weathering.
3. What observations confirmed the presence of a chemical reaction?
1. It is important to explain that not all chalk is made of the same materials and therefore will react at different rates. Why? (Chalk sticks are made of different compounds and different binders to hold the particles together.)
2. Have students explain what would happen to the chalk after years of exposure to acidic solutions. (It would gradually be worn away.)
1. Have each student use a nail or similar item to carve images into a small piece of chalk.
2. Label the containers for each group.
3. Fill the clear containers with vinegar
4. Drop the chalk carving into the vinegar.
5. Observe the reaction.
6. Observe changes the next day.
1. Conduct research on the formation of limestone and prepare a pictorial essay on the types and uses of limestone.
2. Using data collected from this activity, describe the limitations to using limestone rock as a building material.
(Susceptible to chemical weathering in acidic environments.)
Social Studies
• 4-ESS2.A: Rainfall helps to shape the land and affects the types of living things found in a region. Water, ice, wind, living organisms, and gravity break rocks, soils, and sediments into smaller particles and move them around.
• 3-5-ETS1-2: Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.
• 3-5-ETS1.B: Developing possible solutions
• 3-5-ETS1-3: Plan and carry out fair test
• W.5.7: Conduct short research projects that use several sources to build knowledge through investigation of different aspects of a topic.
Suggested Reading/Resources
1. Water Pollution by Rhonda Lucas Donald
2. Air and Water Pollution by Gerald Leinwand
3. Cracking Up: A Story About Erosion by Jacqui Bailey
4. Spring Waters, Gathering Places by Sandra DeYonge
5. A Drop Around the World by Barbara S. McKinney
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