« Return to AACT homepage

AACT Member-Only Content

You have to be an AACT member to access this content, but good news: anyone can join!


Need Help?

Break It Down! (3 Favorites)

LAB in Observations, Chemical Change, Chemical Change, Acid, Interdisciplinary, Physical Change, pH, Chemical Change. Last updated June 12, 2017.


Summary

In this lab, students will examine the physical and chemical changes that take place within a landfill by composting leftover fruits and vegetables from their lunches. They will also record pH and temperature measurements during the process.

Grade Level

Middle school

Objectives

By the end of this lab, students should be able to

  • Determine, through research and classroom discussions, what is necessary in order for composting to occur.
  • Measure and record data, including pH and temperature, to determine whether chemical reactions are occurring.
  • Record observations of physical and chemical changes that occur during composting.
  • Build and maintain a composting bin.

Chemistry Topic

  • Chemical Change
  • Physical Change
  • Observations

Time

Teacher Preparation: minimal

Lesson: one class period

Materials

  • Two liter soda bottles
  • Soil
  • Newspaper-shredded into small pieces
  • Utility knife
  • Food scraps (vegetables and fruits)
  • Worms (preferably red worms)
  • pH meter or paper with color-scale
  • Thermometer
  • Graph paper
  • Water

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Make sure your compost bin has vent holes, as these are necessary for the worms and decomposers to breathe.
  • Composting in a sealed bin can lead to accumulation of dangerous gases. Do not include meats or dairy products as they smell bad.

Teacher Notes

Background and Additional Safety Information:

  • The teacher should cut the bottles with a utility knife to avoid injury. Make sure there are air holes available as the worms will need oxygen. Do not use a closed or air-tight bin for composting as composting can combust. See the InterNACHI article regarding other composting hazards.
  • Show students this video on composting.
  • Do not use dairy or meat products in the composting bins. Adding meats and dairy products can produce very bad odors, can attract pests, and will lead to the production of more anaerobic bacteria, which can affect the composting process, leading to higher acidity. See this article for more explanation.
  • This is a great additional resource regarding composting in schools.
  • According to Cornell, compost microorganisms work best under slightly acidic to neutral conditions. As composting occurs, mature compost will register between 6 and 8 for the pH.
  • Allow students to create their own compost bin, choosing from a variety of materials. This will allow students to compare results with other groups to determine which items are best for composting.
  • The teacher should create a control bin, for students to compare their data and observations with during the composting time. Also, maintaining a similar data table for the control compost bin is advised.

Cross-Disciplinary Extensions

Connect to Math
Students can investigate the differences between the pH of their compost bins with the pH of soil around the school and determine how a change in pH could affect the types of plants that can live in that soil. Students can graph changes in pH.

Connect to Reading
Students can read about how factories and car exhaust can lead to acid rain, which contributes to soil acidity. They can investigate how acidic soil affects the organisms that can live there.

Connect to Writing
Students can write a RAFT-role, audience, format, and topic- to write a letter to people in the community encouraging them to compost.

Connect to Social Studies
Students can investigate landfill use and how recycling helps limit landfill growth. They can also look at things that other cities/states/countries are doing to help.

For the Student

Background

Composting occurs naturally as organisms work to break down organic substances. As these substances are broken down, nutrient-rich material, called compost, forms.

In this lab, you will be designing and building a compost bin. You will first research the necessary items for building it. Then, you will build it and monitor it over time. You will test the pH and the temperatures of the bins on Mondays and Thursdays and document your results. You will compare your results with other groups to determine which elements of the compost bins work the best.

Prelab Questions

You will watch a video about composting, based on your prior knowledge and the information shared in the video, answer the following questions:

  1. What is a landfill?
  2. What is composting? Why is it important?
  3. What is pH?
  4. What is an acid? What is a base? How is pH connected to each?
  5. What is the difference between a chemical and a physical change?
  6. What is a decomposer? How does it help the environment?

Problem

How can food waste be recycled into something beneficial to the environment?

Materials

  • Two liter soda bottle
  • Soil
  • Newspaper-shredded into small pieces
  • Food scraps (vegetables and fruits)
  • Worms
  • pH meter/paper
  • Thermometer
  • Water

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
  • Make sure your compost bin has vent holes, as these are necessary for the worms and decomposers to breathe.
  • Composting in a sealed bin can lead to accumulation of dangerous gases. Do not include meats or dairy products as they smell bad.

Procedure

  1. You will be creating a compost bin in class. Add the following ingredients to your soda bottle:
    a. A handful of soil
    b. Shredded newspaper
    c. Water – enough to make it damp.

  2. The following are independent variables that can be changed within your bin or added to your bin. Please only choose one:
    a. Heat added by placing it under a heat lamp
    b. Choice of vegetables or fruit
    c. Place your bin in a dark place
    d. Adding red worms
    e. Different amounts of components listed in the required section.

  3. Record your independent variable in the space provided below.
  4. Hypothesize what effect your variable will have on your compost bin. Write this in the space provided below.
  5. Design your compost bin. Draw a labeled sketch of the compost bin and its contents in the space provided below.
  6. Every Monday and Thursday, using a pH meter or paper and thermometer, measure the pH and temperature of your compost bin as well as your observations. Record this data in the table provided below.

Data

Independent variable:

Hypothesis Statement:

Labeled Sketch of Compost bin:

Date: pH: Temperature: Obeservations:

Analysis

  1. What changes did you see in the pH levels over time? Did your compost become more acidic, more basic, or is there no change? Why do you think changes in pH occurred?
  2. What changes did you see in the temperature over time? Why do you think these changes in temperature occurred?
  3. Compare the data collected from your compost bin to the data from the control bin. What was different between yours and the control?
  4. How did your independent variable cause a change that was different from the control? If no changes occurred, what might you have done differently to help your fruit or vegetable decompose?
  5. Inspect other compost bins in your classroom and compare the results to your own. Based on this, what do you think would be the best combination of variables to promote composting?

Conclusion

Describe how we can recycle our food waste into something useful to the environment.