In this lab, students will be given a test tube with four substances with unknown identities to the students. They will mix the substances in the test tube and recreate the original four layers through chemical and physical means.
Middle School, High School
This activity will help prepare your students to meet the following scientific and engineering practices:
- Scientific and Engineering Practices:
- Analyzing and Interpreting Data
- Planning and Carrying Out Investigations
By the end of this lesson, students will:
- Record observations and use chemical and physical properties to separate a mixture.
This lesson supports students’ understanding of:
- Chemical properties
- Physical properties
- Separating mixtures
Teacher Preparation: 30 minutes
Lesson: 45-60 minutes
For each group:
- Test tube with four (unknown) layers
- Empty test tube
- Hot plate
- Stirring rod
- Filter paper
- Other materials as students request
- Always wear safety goggles when working 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.
- Students should exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
- The following substances are possible layers, but other substances can be substituted: sodium chloride, iron filings, sand, and wood shavings.
- I do not tell the students what the substances are.
- This is a relatively simple lab to prepare. The lab is inquiry and students can be given very little prompt to successfully separate the mixture and return it to its original state within the test tube.
For the Student
- Obtain a test tube. It should have four distinct layers.
- Record observations about each layer. Be sure your observations are organized and easy to follow.
- Mix the substances by holding the stopper with your thumb and tilt the test tube back and forth.
- Record additional observations after mixing.
- Now separate the mixture. Record the steps you take in the space provided below. Identify whether the process used to separate a particular layer was based on a physical or chemical property.
- Using the separated components, recreate the original test tube.
- Based on your observations and the properties you used to separate the mixture, suggest a possible identity for each part of the mixture.
Organize and record your observations of the layers and the mixture in the space below.
List the procedures you used to separate the mixture in the space below. Identify whether each step used a physical or chemical property to separate the mixture.
Did you separate the mixture and recreate the test tube using chemical changes, physical changes, or both kinds of changes? Explain. What do you think each of the substances in the test tube might be? Justify your conclusions based on the properties you used to separate them.