ACS: Inquiry in Action - Substances Have Characteristic Properties (Lesson 2.3): Mixing Liquids to Identify an Unknown Liquid

Students test four known and one unknown liquid with water to investigate the question: Can you identify an unknown liquid based on how different liquids interact with water?


Students will be able to plan and carry out an investigation to identify a liquid based on how it interacts with water. Students will also be able to explain, on a molecular level, why different liquids act differently when mixed with water.

Key Concepts

  • The way a liquid mixes with water is a characteristic property of the liquid and can be used to identify the liquid.
  • For a “mixing test” to be fair, the same amount of each liquid should be mixed in the same way.
  •  The different atoms and molecules that make up a liquid cause it to mix with water in a characteristic way.

NGSS Alignment

  • NGSS 5-PS1-3: Make observations and measurements to identify materials based on their properties.
  • NGSS 5-PS1-1: Develop a model to describe that matter is made of particles too small to be seen.


  • Students will test the same liquids as in Lesson 2.2 – water, salt water, alcohol, and detergent solution.  But in this activity, all the liquids tested are colored yellow.
  • Students will mix these liquids with water that has been colored blue to see if the liquids have a characteristic way of mixing with water.
  • Students will use their results to identify an unknown liquid that is the same as one of the known yellow liquids. The unknown in this lesson is salt water.


Download the student activity sheet 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