Rainbow pH Demonstration (Kathryn Smith)

Author

Kathryn M. Smith, William S. Hart High School

Principles

• Density

• Acid-Base Indicators

• Acid-Base Reactions

• The pH Scale

Standards

• HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

• PS1-B Chemical Reactions:

  • The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Materials needed

• A large graduated cylinder (250 mL to 500 mL)

• Sodium Carbonate (Na₂CO₃)

• 1.0 M Hydrochloric Acid (HCl)

• ~5 mL of Universal Indicator (Can order from Flinn ~$25 for 1000 mL)

Procedure

Provide a step by step procedure that explains how the demonstration equipment should be used.

Explanation

Provide a solid scientific explanation for the principles illustrated by the demonstration equipment.

Questions

It's very possible that after seeing the rainbow in the graduated cylinder, that students would be naturally curious about the following things. See if they can generate the questions before you ask them.

1. Why don't the layers mix?

2. What causes the colors?

3. What happens if you mix all the layers?

Everyday examples of the principles illustrated

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Photos

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Movies

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References

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