• 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

• Waterproof marker
• Watch/clock, stopwatch or timer

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.

1. Gather supplies.
2. 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.
3. Make copies of the Attack Worksheet.

1. Pass out Attack Worksheet and Acid KWL chart. Have students fill in "Know" section of KWL chart (optional).
2. 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.
3. 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).
4. Pass out the prepared cups of liquid, three nails and three pieces of chalk to each group.
5. 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.
6. 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.)

Figure 3. Activity set up: testing for acidity. click for copyright

1. While students are waiting, have them measure the pH of each of the three liquids with litmus paper.
2. After ten minutes, have students remove the chalk from the liquid and draw a new picture of the changed chalk on their worksheets.
3. 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).

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.

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.