SummaryIn this activity, students explore the effect of chemical erosion on statues and monuments. They use chalk to see what happens when limestone is placed in liquids with different pH values. They also learn several things that engineers are doing to reduce the effects of acid rain.
Engineers consider the possible effects of acid rain on the health of humans and the environment when they investigate damage to bodies of water, wildlife, forests, crops and contamination of the drinking water supply. Engineers have helped to develop laws that prevent or limit large factories and industries from burning fossil fuels or that require them to minimize their pollutant output. And, they have also developed many useful technologies to help reduce the harmful pollutants in the air, including better air cleaners and air filtration systems for industry and energy-efficient cars and appliances.
After this activity, students should be able to:
- Give examples of common acids and bases.
- Describe acid rain and chemical erosion and how they affect the environment.
- List several things that engineers are doing to reduce acid rain and its effects.
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Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
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For each group:
- ½ cup tap water
- ½ cup lemon juice
- ½ cup white vinegar
- 3 pieces white chalk (larger chalk pieces with a flat surface, if possible, these are easier for the students to decorate)
- 3 small cups labeled with group names (clear plastic cups work best)
- 3 nails (or other sharp objects that could scratch chalk)
- 3 strips litmus paper
- 3 copies of the Attack Worksheet and Acid KWL Chart
For the teacher/instructor:
- Waterproof marker
- Watch/clock, stopwatch or timer
What do you know about acids and bases? Did you know that almost every liquid you see is an acid or a base (with the exception of distilled water, which is just water)? The amount of tiny particles — called ions — in a liquid decide if something is an acid or a base. We use something called pH to measure whether a liquid is an acid or a base. There are many acids and bases around your own home. Bleach and household cleaners are examples of bases. Did you know that a really strong acid or base can break something apart? If you add straight bleach to a piece of clothing, it can take the color away or even put a hole in the item. An example of an acid around your home is lemon juice, vinegar and cola. Very strong acids can put holes in items as well. Today we are going to see what an acid can do to a basic building material, limestone.
Acids can also be found in the air around us — specifically in polluted air. Acid rain happens when air pollution chemicals, which come from fuel-burning factories or cars, react to form acids in the air. The acids from burning fuel in the air attach to water molecules in the air and fall as rain or snow. We call the breakdown caused by acid rain, chemical erosion. The effects of acid rain (chemical erosion) include: damage to statues and buildings; weakening of the exposed metal on bridges and playground equipment; damage to wildlife, plants, forests and crops; and the contamination of drinking water supplies.
Two materials used often in building countertops and floors are limestone and marble, which both contain calcium carbonate. In fact, many historical buildings and monuments are built out of limestone and marble as it was readily available at the time of their construction. For example, many of the monuments in Washington D.C. are made of marble. Acid rain is harmful to many of these monuments and buildings because the acid breaks down the calcium carbonate in them more quickly than with other building materials. Figures 1 and 2 illustrates chemical erosion.
Acid rain is formed by complex chemical reactions involving air pollution. The two main pollutants in acid rain are oxides of nitrogen and sulfur that react with rain moisture to form nitric and sulfuric acid. Mainly, these erosive pollutants come from manmade sources such as cars or fossil fuel-burning plants. Acid rain contaminates the environment not just through rain, but also through snow, fog, dew and dust.
Lemon juice and vinegar are the acids used in this activity to simulate acid rain. Chalk is made up of limestone, which will simulate a statue. Limestone contains calcium carbonate (CaCO3), which will react chemically with the acid, causing it to deteriorate or erode. This happens because the acid causes the calcium (Ca) and carbonate (CO3) in the limestone to separate into calcium and carbon dioxide gas (CO2).
Although the lemon juice and vinegar acids used in this activity are actually more concentrated than acid rain, they successfully demonstrate the erosive effects of acid rain over time.
Before the lesson
- Gather supplies.
- Prepare three cups for each group, one containing tap water, one with lemon juice and one with vinegar. Clearly label each cup using a waterproof maker with the group name and the liquid each cup contains.
- Make copies of the Attack Worksheet.
With the students
- Pass out Attack Worksheet and Acid KWL chart. Have students fill in "Know" section of KWL chart (optional).
- Discuss how and why acid rain occurs and how acid rain can chemically erode many limestone statues and monuments. Explain that engineers work to stop acid rain by finding cleaner ways to create energy as well as modifying existing technologies (cars, industrial plants, etc.) so that they create less air pollution and acid rain.
- Show pictures of chemical weathering. Explain to students that rain is normally a little acidic to begin with, but sometimes it can become even more acidic because of pollution. The amount of damage that acid rain causes depends on how acidic it is. Also explain that damage can occur with just a little bit of acidity over long periods of time. Have students complete the "Want to Know" section of their KWL charts (optional).
- Pass out the prepared cups of liquid, three nails and three pieces of chalk to each group.
- Have each student use a nail to carve a picture in one piece of chalk. Then, have students draw a picture of their chalk on their worksheets. Tell them the picture does not have to be exact; it can just be a quick sketch.
- When finished, each group member should put their piece of chalk in a container of liquid (as shown on Figure 3: one piece of chalk in each of the cups of water, lemon juice or vinegar) and wait 10 minutes. (Note: it is suggested that the teacher set a timer or stopwatch to monitor the time.)
- While students are waiting, have them measure the pH of each of the three liquids with litmus paper.
- After ten minutes, have students remove the chalk from the liquid and draw a new picture of the changed chalk on their worksheets.
- Finally, students should compare their chalk with the other members in their group and fill out the remainder of the worksheet. Have students complete the "Learned" section of the Acid KWL chart (optional).
Students should not eat or drink any of the liquid or other materials used during activity.
If using nails, remind students to use them ONLY for carving their chalk; they should not poke or scratch their classmates, tabletops or walls.
If necessary, the tip of a ballpoint pen or pencil may be used instead of nails to carve into the piece of chalk; please keep in mind, however, that it may ruin the writing implement.
What should happen: The chalk in the lemon juice and vinegar should dissolve such that students should not be able to see their pictures. If this does not happen:
- Try leaving the chalk in each liquid longer (or the specific liquid that did not dissolve the chalk).
- Try using more concentrated vinegar or lemon juice.
Discussion Questions: Solicit, integrate and summarize student responses.
- What do you know about acids? (Possible answers: it is a substance that has a high pH, often tastes sour, turns litmus paper blue and can break things apart.)
- Can you name any acids? (Possible answers: lemons, vinegar, cola, car battery acid, and hydrochloric acid.)
Know / Want to Know / Learn (KWL) Chart: Before the lesson, ask students to write down on their Acid KWL Chart (or in the top left corner of a piece of paper or as a group on the board) under the title, Know, all the things they know about acid rain. Next, in the top right corner under the title, Want to Know, ask students to write down anything they want to know about acid rain. After the lesson, ask students to list in the bottom half of the page under the title, Learned, all of the things that they have learned about acid rain. Ask students to name a few items and write them on the board.
Activity Embedded Assessment
Prediction: Have the students predict what will happen when they put their chalk into the liquid and record predictions on their worksheet.
Attack Worksheet: Have the students complete the activity worksheet; review their answers to gauge their mastery of the subject.
Question/Answer: Ask the students and discuss as a class:
- What causes acid rain? (Answer: Acid rain happens when air pollution — from fossil fuel-burning plants or cars — chemicals react to form acids in the air. The acids in the air then attach to water molecules and fall as rain or snow.)
- What effects does acid rain have on statues and monuments? (Answer: Acid rain can dissolve away statues, monuments and buildings over time.)
- How do engineers try to clean up acid rain? (Answer: Engineers work to find ways other than burning fossil fuels to get energy, such as electric cars. Engineers also design filters for smoke stacks so less air pollution is released into the atmosphere from industrial factories.)
Know / Want to Know / Learn (KWL) Chart: Finish the remaining section of the KWL Chart as described in the Pre-Lesson Assessment section. After the lesson, ask students to list in the bottom half of the page under the title, Learned, all of the things that they have learned about acid rain. Ask students to name a few items and write them on the board.
Extend the activity by leaving the chalk in the containers of liquid and wait a few days to see when/if the chalk completely dissolves. Students can record how many days it took the chalk to dissolve for each liquid and make a representative line graph of the data. This simulates the effect of acid rain over a longer period of time. Try adding other items to the liquid, such as leaves, metals or plastic.
Try other common acids and bases and see what affect they have on chalk, leaves or other common items. For example, use cola (acid) or oven cleaner (base).
Make a flyer or poster about why engineers care about acid rain. For example, students can express that acid rain damages building, car paint and ecosystems. Have students draw a picture of something an engineer could do to help reduce acid rain.
ContributorsJessica Todd; Melissa Straten; Malinda Schaefer Zarske; Janet Yowell
Copyright© 2006 by Regents of the University of Colorado.
Supporting ProgramIntegrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.