How to Teach Students about Acid and Acid Rain
How acidic is your rainwater? Use these lesson plans to get students thinking about how acids affect the environment in which we live.
By Jennifer Sinsel
As an elementary teacher specializing in math and science, I often work with others on my team to develop interdisciplinary units. Sometimes this happens purposefully; sometimes by accident! One such example of an accident occurred several months ago when all of our upper elementary students were studying the Civil War era. We took a field trip to a nearby cemetery so students could make rubbings of different headstones and research the lives of the people. Several students noticed that the older headstones were more difficult to read, and the lettering on some of the oldest was nearly impossible to make out. Their curiosity piqued, students wanted to understand how the headstones could be so dilapidated when they were made out of stone. This discussion led to an unplanned, yet high-interest, science unit on the acidic properties of rainwater!
Air pollution causes many environmental problems, including smog and depletion of the ozone layer. In addition, air pollution can cause a problem known as acid rain. However, what most people don’t realize is that all rainwater is slightly acidic in its natural form, which can cause weathering of rocks and man-made structures over time. This natural weathering is what my students noticed at the cemetery, and it is also the reason that monument engravers started using harder, more weather-resistant rock such as granite in place of limestone for grave markers. Areas with higher amounts of acid rain will see more weathering on buildings and monuments; locations with normal rainwater will see less.
To understand the concept of how acids dissolve substances, students must first learn about pH, the measure of how acidic or basic a substance is, and it is measured using a scale of 0 to 14. Any substance below 7.0 on the pH scale is an acid, while any substance above 7.0 is a base. A substance closer to either end of the scale is a stronger acid or base than substances that are closer to the middle of the scale. Substances of exactly 7.0 are considered neutral (neither an acid nor a base). It should also be explained that the pH scale is logarithmic, which means that a pH of 3 is ten times more acidic than a pH of 4, one hundred times more acidic than a pH of 5, one thousand times more acidic than a pH of 6, and so on.
To illustrate this point, I provide students with a number of substances to test. These might include distilled water, lemon juice, window cleaner, laundry detergent, soft drinks, milk, salt water, vinegar, and antacid tablets (dissolved in distilled water). Students should also collect precipitation (rain or snow) from the area. You can get pH paper from pool supply companies or scientific supply companies and give each group one vial to use in testing.
Students can test the pH by dipping the pH paper into a small amount of each substance and comparing the paper to the color chart on the side of the vial. The pH can then be recorded in science journals or on a teacher-generated chart. If no one mentions it, ask students about possible sources of error using this method (sometimes it is difficult to distinguish an exact color match, and this could result in disagreements or inaccurate data). To minimize error, I usually ask each group to record their results on the board, and we average that data to obtain our “final” pH. For those with higher budgets, accurate pH meters can be purchased from scientific supply companies. As an extension, students can collect precipitation throughout the year to track how acidity may or may not change with the seasons.
For more activities related to acids and acid rain, try one of the following lesson plans.
Acid Rain Lesson Plans:
It is important to not only discuss pH when exploring the weathering of buildings and monuments, it’s also vital to maintaining the health of our soils and water supply. In this lesson, students explore pH levels of different substances and learn about the importance of maintaining a balance between acid and base in soil.
In this excellent lesson, students study the life cycle of shrimp and how the pH levels of the water affect their hatching and survival.
Students conduct an experiment to explore how acid rain affects both living and nonliving objects. They then link this to the bigger picture, discussing how engineers examine the effects of acid rain and design technologies that reduce the amount of pollution released into the air.