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The Disappearing Color (2 Favorites)

LAB in Mixtures, Reaction Rate, Chemical Change. Last updated December 20, 2018.


Summary

In this lab, students will create a solution to observe a chemical change between food coloring in water and bleach. They will also develop the process skills of predicting, observing, and measuring temperature.

Grade Level

Elementary School

Objectives

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

  • Create a solution of water, food coloring and bleach.
  • Predict and observe a chemical change.
  • Measure and record temperature change.

Chemistry Topics

This lab supports the students’ understanding of:

  • Chemical Reactions
  • Chemical Change
  • Solutions
  • Mixtures
  • Kinetics
  • Reaction Rate
  • Data collection
  • The Scientific Method

Time

Teacher Preparation: 10 minutes

Lesson: 30-40 minutes

Lab disappearingcolor photo1Materials

Per Group:

  • 1 bottle of food coloring
  • 100 ml of Bleach (place in container to start. Refill as needed.)
  • Water
  • 1 Eyedropper
  • 1 Small jar (The size of a baby food jar)
  • Thermometer
  • Metal spoon
  • Timer
  • Other:
    • Disposable gloves
    • Optional: swatches of dark fabric

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.
  • Do not consume lab solutions, even if they’re otherwise edible products.

Lab disappearingcolor photo2Teacher Notes

  • Prior to the demonstration students should have had instruction and experience with solutions.
  • Understanding the reaction: When the bleach mixes with the colored water the food coloring becomes colorless. This occurs because a chemical in the bleach contains oxygen. The oxygen combines with the chemicals in the dye to form a colorless compound. When you add more drops of food coloring the color seems to disappear because it is surrounded by bleach which reacts with it immediate, causing it to change to a colorless solution.
  • To add diversity to the investigation, give each group a different food color. Students will see that different colors will react with the bleach at different rates.
  • Students should determine if the rate to react and become colorless in the bleach solution will differ depending on the color.
  • This lab was inspired by the resource: “Chemistry for Every Kid: 101 Easy Experiments That Really Work”, written by Janice VanCleave (1989)
  • Helpful tips:
    • Prepare materials for pairs of students ahead of time.
    • Don’t assume students know how to operate an eye dropper. Take a moment to demonstrate and have the students practice with plain water.
    • Groups of 2-4 work best in my experience.
  • Optional extension, or for those who finish early: Bring in swatches of dark colored fabric. Create a mixture of water and bleach. Using an eyedropper add drops of the solution onto the swatch and observe any changes.
  • The photograph shows the water and food coloring solution on the left, and the same solution on the right with added bleach.

For the Student

Background

Chemical reactions produce a change in properties from the original materials. Chemical reactions may also produce a change in temperature.

Pre-lab Questions

  1. What is a chemical change? Give an everyday example.
  2. What are some indicators that a chemical change has occurred?

Problem

What is the effect of bleach on colored dye?

Materials

  • 1 bottle of food coloring
  • 100 ml of Bleach
  • Water
  • 1 Eyedropper
  • 1 Small jar
  • Thermometer
  • Metal spoon
  • Timer
  • Disposable gloves

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Clean up your materials and dispose of any chemicals according to your teacher’s instructions.
  • Do not consume lab solutions, even if they’re otherwise edible products.

Procedure

Part 1:

  1. Fill the jar halfway full with water.
  2. Add 1 drop of food coloring to the water and stir with a metal spoon.
  3. Record the temperature of the colored water in the data table below.
  4. Use the eyedropper to add drops of bleach until the solution turns colorless. Stir the solution after each drop.
  5. Measure the temperature again. Record it in the data table below.

Part 2:

  1. Record the color of your food coloring in the data table below.
  2. Add one drop of food coloring to the colorless solution. Start your timer immediately. Do not stir! Record the amount of time for the single drop of food coloring to become completely colorless.

Data

Part 1

Temperature (C)

Colored water

Colored Water + bleach

Part 2

Color of Food Coloring used

Time for color to change to colorless

Analysis

  1. Was there a temperature difference observed during part 1 of the experiment? Explain why or why not this is important.
  2. Describe what you observed when food coloring was added to the water and bleach solution in part 2.
  3. Can you think of a real world purpose for using a bleach solution?
  4. When the water and bleach solution is disposed of by pouring it down a drain from where will it go? Can you think of any problems it may cause the environment when it reaches a water source? Are there any benefits?

Conclusion

Summarize your findings regarding the effects of bleach on colors in a short paragraph below: