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

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
• Science and Engineering Practices:
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions

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.