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Determining a Chemical or Physical Change (1 Favorite)

LAB in Observations, Chemical Change, Physical Change, Molecular Structure. Last updated October 16, 2019.


Summary

In this lab, students will follow a laboratory procedure that instructs them how to heat a small sample of copper(II) sulfate pentahydrate. Students will make observations in order to determine if a chemical or physical change occurs.

Grade Level

Middle School and High 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.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data
    • Engaging in Argument from Evidence

Objectives

By the end of this lab, students should be able to

  • Differentiate between a chemical and physical change, identifying examples of each.
  • Justify a conclusion based on experimental results.

Chemistry Topics

This lab supports students’ understanding of

  • Physical Change
  • Chemical Changes
  • Observations
  • Molecular Structure

Time

Teacher Preparation: 20 minutes

Lesson: 50 Minutes

Materials (per group)

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.
  • Always use caution around open flames. Keep flames away from flammable substances.
  • Always be aware of an open flame. Avoid reaching over the open flame, tie back hair, and secure loose clothing.
  • If using a match to light the Bunsen burner, be cautious with the flame.
  • An operational fire extinguisher should be in the classroom.

Teacher Notes

  • For lab preparation, it may be best to place a few crystals of Copper(II) Sulfate Pentahydrate in small weight boats for each lab group. This will decrease the time needed to obtain supplies.
  • Students should set up and obtain all supplies prior to getting the crystals.
  • Dispose of crystals per your school’s chemical cleanup procedures, or allow wet crystals to re-crystallize. Use of distilled water to rehydrate in the lab activity is needed if reusing the crystals.
  • Warm up:
    • Ask students to identify the difference between a physical and chemical change. This will include a discussion of clues that show a chemical change has occurred. These could include bubbling (gas production), precipitate formation, energy change (exothermic/endothermic reactions, light production) and production of a new substance.
    • Students could be asked to first brainstorm their ideas individually and then discuss their thoughts with a partner.
    • Engage all students by compiling all student contributions on the board/smartboard/classroom display.
    • Examples of Physical/Chemical Changes may include:
      Physical Changes Chemical Changes
      Changing the size of an object
      Phase Changes
      Dissolving substances (salt into water)
      Changing the color of an object with a dye/marker
      Breaking an object into pieces
      Burning/Combustion
      Mixing acid and base
      Digesting food
      Cooking meat
      Baking bread
      Oxidation of metals
    • Define a hydrate: compounds, typically crystalline that weakly attract water molecules and retain them within the crystalline structure.
    • Show the image of Copper Sulfate.
  • Optional Extension:
    • View the YouTube video: Hydrated Ionic Compounds. The follow up lecture is very dependent on how you arrange your curriculum. If this activity follows basic naming of ionic compounds, it will work nicely to examine how hydrates are named.
    • Lectures or review of content could be as simple as discussing the type of change being physical (the removal of water molecules from a crystal), to a detailed examination of the number of moles of water removed from a sample of the compound.

For the Student

Lesson

Background

Matter can undergo both Physical and Chemical Changes.

Examples of these changes include:

Physical Changes Chemical Changes
Changing the size of an object
Phase Changes
Dissolving substances (salt into water)
Changing the color of an object with a dye/marker
Breaking an object into pieces
Burning/Combustion
Mixing acid and base
Digesting food
Cooking meat
Baking bread
Oxidation of metals

Prelab Questions

  1. In what case would heating a substance cause a physical change to occur? Explain how you would know.
  2. In what case would heating a substance cause a chemical change to occur? For each example, explain how you would know.

Purpose

To determine if a physical change or chemical change occurs as you heat copper(II) sulfate pentahydrate crystals in a test tube.

Hypothesis

I think heating Copper(II) Sulfate Pentahydrate crystals will:

  • Produce a physical change OR Produce a chemical change (circle your choice)
  • Because (explain why):

Materials

  • Copper(II) Sulfate Pentahydrate
  • Scoopula
  • Test Tube Rack
  • Test Tube
  • Test tube holder
  • Bunsen Burner
  • Striker/Matches

Procedure

  1. Place one or two crystals of Copper(II) Sulfate Pentahydrate in the bottom of a clean, dry test tube.
  2. Observe the crystals and record the color and appearance in the data table provided.
  3. Heat the crystals gently with a low flame while inclining the test tube on its side. *Your teacher will demonstrate this set-up.
  4. Record your observations of the crystals and the inside of the test tube while heating it.
  5. Heat the whole test tube until no more changes occur.
  6. Make a detailed observation of the remaining substance in the test tube.
  7. After the test tube has cooled, add 2 drops of water to the crystals and observe any changes that occur.

Data

Process Observations of crystals
Prior to heating
During heating
After heating has ended
Addition of water

Conclusion

Did the heating of the Copper(II) Sulfate Pentahydrate crystals produce a chemical or physical change? Give evidence for your conclusion:

Post-lab Questions

  1. Do you think that the amount of crystals would have an effect on what took place? WHY?
  2. What was the major change in the crystals that you observed?
  3. What do you think is the reason for the crystals changing colors (as a result of the heating)?
  4. Discuss how your conclusion addressed your hypothesis? Did you change your mind after adding water to the crystals in your test tube?
  5. What does it mean to have “dehydrated” milk (or other food) and how does this relate to the crystals in our lab activity?
  6. What is something new you learned when completing this activity?