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The Diffusion of Gases Chemical Demonstration Kit reveals the motion of ammonia and hydrochloric acid gas molecules by their colorful reactions with acid–base indicators. Molecules are moving. Discover proof of this incredible statement.

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Molecules are moving! What proof is there for this incredible statement, and what factors influence the kinetic energy of moving molecules? Demonstrate the motion of invisible ammonia and hydrochloric acid gas molecules by their colorful reactions with acid–base indicators. Then compare the rates of diffusion of different size molecules by reacting the two gases together in the ammonium chloride “ring test.” Finally, show the effect of temperature and use the teaching analogy provided with the kit instructions to illustrate the relationship between temperature and kinetic energy. Large, 14 mm x 30 cm glass demonstration tubes are a perfect size for viewing by all students.

Concepts: Diffusion, kinetic-molecular theory.
Time Required: 15 minutes
Materials Provided: Ammonium hydroxide, hydrochloric acid, phenolphthalein, thymol blue, Beral pipets, cotton balls, two glass diffusion tubes, medicine droppers, rubber stoppers.

Note: Perform this demonstration in a fume hood or well-ventilated lab.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Developing and using models
Analyzing and interpreting data
Constructing explanations and designing solutions

Disciplinary Core Ideas

MS-PS1.B: Chemical Reactions
MS-PS1.A: Structure and Properties of Matter
MS-PS3.A: Definitions of Energy
HS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter

Crosscutting Concepts

Systems and system models

Performance Expectations

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.