ACS: Inquiry in Action - Substances Have Characteristic Properties (Lesson 2.2): Identifying an Unknown Liquid

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


Students will be able to plan and carry out an investigation to identify a liquid based on how it interacts on different paper surfaces. Students will also be able to explain that since different liquids are made of different atoms and molecules, they act in their own characteristic way.

Key Concepts

  • When observing different liquids, the way a liquid acts on paper is a characteristic property of the liquid and can be used to identify it.
  • For the test to be fair, the same amount of each liquid should be placed on the paper in the same way.
  • The different atoms and molecules in a liquid interact with the paper in a characteristic way.

NGSS Alignment

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


  • Students will test four known liquids and an unknown liquid on two different paper surfaces. They will use their observations to identify an unknown liquid.
  • Students will realize that by using a combination of results from two tests, they can successfully identify an unknown liquid.
  • Students will also add water and salt water to green food coloring on a coffee filter. They see a distinct difference in the way each liquid makes the colors in green food coloring separate.


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)

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