Acids, bases and solutions

Project - Raising Trout

Raising trout from eggs to fry in the classroom is a fabulous way for students to observe and study the life cycle of vertebrates and simultaneously learn about threatened species in local watersheds. Many states have programs where teachers and students raise trout in their classrooms in partnership with the Department of Fish and Wildlife for later release into a designated lake, creek or river. Described here is information for teachers on how to partner with state agencies, fish hatcheries, and local fly-fisher groups to raise rainbow trout in the classroom. A worksheet for the trout release field trip is provided. Best of all, many Trout in the Classroom Programs are fully supported by local fly-fisher groups and the California Department of Fish and Game (such as the California program that I participated in), and thus there is no materials cost to the teacher beyond the costs of organizing the trout release field trip at the end of the project.

6. Cell Energy - Colorful Respiration

Blow through a straw into bluish liquid and watch it turn green then yellow before your eyes. Put some plants into the yellow liquid, leave it in a sunny window, come back the next day and the liquid is green. What if you leave the plants in the dark? What if you put some pond snails in? What if you put both pond snails and plants? What’s going on?

The liquid is bromthymol blue (BTB) a non-toxic acid-base indicator that can be used to indirectly measure levels of dissolved carbon dioxide (CO2). The amount of CO2 in a solution changes the pH. An increase in CO2 makes a solution more acidic (the pH gets lower). A decrease in CO2 makes a solution more basic (the pH gets higher). The reason for this is that carbon dioxide that is dissolved in water is in equilibrium with carbonic acid (H2CO3).

CO2 + H2O ↔ H2CO3

In any solution, while the majority of CO2 stays as CO2, some of it is converted to H2CO3, turning the solution slightly acidic. If CO2 is added to the water, the level of H2CO3 will rise and the solution will become more acidic. If CO2 is removed from the water, the amount of H2CO3 falls and the solution becomes more basic. Thus, acid-base indicators such as BTB can indirectly measure the amount of CO2 in a solution.

For more than you ever wanted to know about carbonic acid, see the Wikipedia article on carbonic acid. For the example lesson plans developed by Bob Culler through Access Excellence at the National Health Museum. For a great time lapse video showing BTB color changes using elodea and snails, see Activity C13 from Addison-Wesley’s Science 10 curriculum.


  • Bromthymol blue (BTB can be ordered from any science supply company such as Flinn Scientific $9 for 1 liter 0.04% BTB solution).
  • Several 2 liter soda bottles
  • Test tubes
  • 500 ml beakers or disposable plastic or paper cups
  • Water (since the pH of tap water varies, you may wish to use distilled water for your master BTB solution)
  • Drinking straws
  • Plastic wrap
  • Elodea
  • Pond snails


  1. Before the lesson, the teacher should mix a master BTB solution in one or more 2 liter soda bottles. For each 2 liter bottle, mix 120 ml 0.04% BTB with 1800 ml water. The end result should be a medium blue master BTB solution, dilute enough to be safe for plants and snails but dark enough to see the color changes.
  2. Pour 200 ml diluted BTB in a beaker or cup.
  3. Take a deep breath then blow bubbles in the BTB solution through a drinking straw. What happened? Why?
  4. Set up a test tube rack with 3 tubes. In tube #1 put unbubbled BTB solution (blue). In tube #2 put bubbled BTB solution (yellow). Tubes #1 and #2 will be your comparison tubes. In tube #3 you have a choice of what to do. Choose one option from each of the following columns:
    BTB solution Living things
    Light conditions
    bubbled BTB (yellow) spring of Elodea Sunny window/bright light
    unbubbled BTB (blue) 5 pond snails Dark closet/drak heavy cloth
    both Elodea and 5 pond snails  
  5. Make a hypothesis about what will happen to your tube.
  6. After 24 hours, check the color of your tube. What happened? Why?

Going Further

6. Cell Energy (photosynthesis and respiration)

Here you will find a toolbox full of inquiry investigations on photosynthesis and respiration. Rather than the detailed lesson plans provided elsewhere at My Science Box, each experiment only contains a short background, materials, procedure, and going further section. It is up to you to decide which of the many experiments you wish to try with your students and how to sequence them. You will find everything from descriptions for how to extract chlorophyll, discover that plants “breathe”, recreate the experiments of Priestly and Ingenhousz, detect carbon dioxide production, and measure the rate of yeast respiration. None of these experiments require expensive equipment such as metabolism chambers or oxygen meters although those are great tools if you can afford them.

Assessment - Life on Mars

Mars Exploration Rovers: This special-effects image combines a model of the Mars rover Opportunity and 46 photogrpahs that Opportunity took of "Burns cliffs" near the edge of "Endurance Crater". Image courtesy of NASA/JPL-Caltech/Cornell.Mars Exploration Rovers: This special-effects image combines a model of the Mars rover Opportunity and 46 photogrpahs that Opportunity took of "Burns cliffs" near the edge of "Endurance Crater". Image courtesy of NASA/JPL-Caltech/Cornell.

In the summer of 2003, NASA’s Jet Propulsion Laboratory launched two Mars Exploration Rovers - Spirit and Opportunity - towards Mars. They landed on January 3rd and 4th, 2004. Their primary scientific goal was to study the geology of Mars and search for signs of water. Although they were expected to last only 3 months, they have been vigorously sending back data for over 2 years and are still going strong! In this activity, students receive simulated Martian soils and are given the task of designing 3 tests to determine whether the soil sample contains something alive or something that was once alive. They may use any of the tools from the previous lessons – agar plates, tests for organic molecules, microscopes, or something of their own design. This assignment allows students an opportunity to demonstrate what they have learned throughout the unit, both about scientific experimentation and about the special characteristics of living things.

Can describe the necessary characteristics of life.
Can categorize objects as alive or not alive using self-generated data.
Can demonstrate that all living things will grow and reproduce when provided with the proper nutrients and environmental conditions.
Can demonstrate that living things are made of organic molecules.
Can test for the presence of protein, glucose and starch.
Can design an experiment.
Can make observations and keep track of data over several days.
Can interpret the results of an experiment.

Organic molecule
Biuret solution
Benedict’s solution

3. Testing for Life's Molecules

All known life is made out of a small group of chemical compounds called organic molecules. Common organic molecules include proteins, glucose, starch, lipids, and nucleic acids. This lesson plan asks students to conduct tests for proteins, glucose, and starch. At the beginning of the activity, they choose 3 items to test: one known to be “never alive”, one known to be “once was alive”, and one mystery item. In addition, each station includes a positive control. By the end of the experiment, students should be familiar with some of the major organic molecules and should recognize that living things, and substances derived from them, are made of organic molecules. In addition, this is a chance to bring in topic surrounding nutrition, health, and digestion. Since our bodies are made up of organic molecules, we need each of these molecules as nutrients in our food.

Project - Terraqua Column Experiment

Once students have some experience working with a basic terraqua column (see the Terraqua Columns Lesson), they have an opportunity to design and conduct their own investigations with their mini-ecosystems. There are hundreds of variables students can manipulate with a minimum of materials – temperature, light, pollution, type of water, type of soil, etc. As a class, students brainstorm variables that might affect the plants, soil, and/or water in a terraqua column. In teams, students propose a project, and once approved, set about testing their ideas and observing the effects of their manipulations on their mini-ecosystem. If your school participates in a local science fair, this is a fantastic activity to introduce students to experimental design, variables, and control groups.

7. Habitat Survey


In this activity, students finally get to apply their skills of soil analysis and observation to a 1 meter by 1 meter area of the schoolyard, restoration site, or creek bank. Teams of students get down and dirty exploring the soil, vegetation, and insect life in their microhabitat. Students practice using the soil analysis tools they learned previously and also practice using field guides to identify plants and insects. Upon returning to the classroom, they compare their results with other groups to see the differences and similarities between their microhabitats. This is a superb activity to use before and after a habitat restoration project or simply to track changes in a habitat throughout the year. I used this investigation to introduce the idea of native vs. non-native species and to begin a debate about invasive species. My students really “got it” when they examined our adopted restoration area and discovered that there was a monoculture of invasive, non-native English ivy all across our site. They visited our adopted site 3-4 times throughout the year pulling ivy and planting native plants. When all was said and done, they repeated this investigation in the spring to discover exactly the magnitude of the change they made on the environment – and to find that the native plants recruited a wider variety of insects than they had seen at that site in the fall.

Field Trip - Point Reyes


This section will give you information to help you plan a field trip to Point Reyes National Seashore. My classes went to Point Reyes for an overnight camping trip between lessons 7 and 8. The first day, we went to the Bear Valley Visitor Center and did a ranger led program called Monitoring Creek Health. After creek monitoring, we played and hiked at Linmatour beach before retiring to our campsite. The following day, we took a kayaking tour of Tomales Bay. Our kayaking guides taught the students about the wildlife and geology of the area throughout the trip. The happy and exhausted students and teacher then made their way back to school.

3. Soil Analysis

Soil Profile from Tabott county, Tennessee

Students conduct 4 tests of soil quality in the classroom that can then be applied to their terraqua columns and to the outdoors: visual observation, soil separation, pH, and Tullgren Funnel (to isolate living things in the soil). They make comparisons between 2 different types of soil and draw conclusions about how "healthy" each soil is. Through this process, students discover the major "ingredients" of soil: clay, silt, sand, organic material, water, air, living things, and minerals. By recording information in their science journals, they learn how to keep good notes and share the information with others in the class during a concluding class discussion about what "healthy" soil might look like and why.

1. Terraqua Columns


Students discover what ecosystems are by exploring the relationships between him/herself, other living things, and the student's environment. Students create and study miniature ecosystems by building a terraqua column - a 2 story soda bottle tower with soil and plants on the top and a water source on the bottom. The terraqua columns will be used throughout the ecology unit for practice with water and soil quality monitoring and with making and recording observations. Later in the unit students can conduct independent investigations with their terraqua columns.