ACS: Inquiry in Action - Substances Can Mix and React to Form New Substances (Lesson 3.3): Forming a Precipitate

Students combine an Ivory Soap solution with an Epsom salt solution to produce a solid “soap scum” to investigate the questions: What happens when you mix soap with hard water? and Is soap scum different from soap?


Students will be able to explain that mixing substances can cause a chemical reaction that results in the formation of a new substance. Students will be able to plan and carry out an investigation to compare the amount of bubbles produced by a solid “soap scum” precipitate with the bubbles produced from soap. Students will also be able to explain that different substances react in a characteristic way that can be used to identify a substance.

Key Concepts

  • Mixing substances can result in a chemical reaction that produces new substances.
  • Two liquids can chemically react to produce a solid.
  • Substances have characteristic chemical reactions that can be used to identify a substance.
  • Designing a fair test to study chemical reactions requires keeping everything the same except for the one thing you want to know about.

NGSS Alignment

  • NGSS 5-PS1-3: Make observations and measurements to identify materials based on their properties.
  • NGSS 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in new substances.


  • Students prepare a soap solution by dissolving Ivory soap in water.
  • Students also make an Epsom salt solution to simulate hard water.
  • Students combine the soap solution with the Epsom salt solution to produce a solid “soap scum” precipitate.
  • Students then carry out a bubble test on the solid soap scum and Ivory soap to determine if they are different.

The two main ideas for students to understand from this activity are that mixing substances can result in the formation of a new substance, and that the way different substances react is a characteristic property that can be used to identify a substance.


Download the student activity sheet (PDF) and distribute one per student when specified in the activity. The activity sheet will serve as the Evaluate component of the 5-E lesson plan.


Science Topics
Chemistry, Matter
K-6, Educator
5th Grade
Descriptions of PDFs

Lesson Plan (PDF) | Student Activity Sheet (PDF) | Student Reading (PDF) | Teacher Background (PDF) | Connections to NGSS (PDF)

What are you looking for?


ACS (American Chemical Society)

Website URL

Type of Resource

Lesson Plan
PDF File
Video (Instructional)

Assigned Categories