Students place small amounts of scented liquids inside latex balloons, inflate them, and identify the scent over time. The activity models diffusion across a barrier and introduces terms like concentration gradient, semi-permeable membrane, and equilibrium.

1. Check for latex allergies in the class and choose alternative gloves/balloons if needed.
2. Gather several scents (e.g., flavor extracts, essential oils, perfume, or a spice slurry) and choose distinct balloon colors—one color per scent plus one empty control.
3. Using a clean dropper for each scent, place 3–4 mL of a single scent into a balloon, swirl to coat the inside, then inflate and tie it. Make two balloons of each scent if desired.
4. Prepare additional balloons of other colors with different scents. Inflate one balloon with no scent to serve as a control.
5. (Optional) Tie each balloon to a short string and tape to lab tables to keep them in place.
6. Have students rotate among balloons, gently wafting near the nose (no squeezing), and record their best guess for each scent.
7. Lead a discussion: How did the scent travel through the latex? Introduce diffusion, semi-permeable membrane, concentration gradient, and equilibrium.

Smelly Balloons - ASU Open Door:

O Wow Moment: Smelly Balloons - Children's Museum Houston:

📄 Introducing Diffusion with Smelly Balloons - Science Lessons that Rock: https://sciencelessonsthatrock.com/introducing-diffusion-with-smelly-balloons-html/

• Compare diffusion using thick vs. thin balloons or different brands.
• Test water-based extracts versus oil-based scents to see which diffuses faster.
• Place balloons in warm versus cool rooms to observe temperature effects on diffusion rate.
• Time how long it takes before most students can correctly identify each scent; graph class data.
• Replace latex with non-latex balloons to accommodate allergies and compare results.

• Screen for latex allergies; provide non-latex balloons if needed.
• Do not open or taste the scents; some extracts and essential oils can irritate skin or eyes.
• Use minimal amounts of strongly scented materials and maintain ventilation for sensitive students.
• Assign one scent per color and separate filling tools to avoid cross-contamination.
• Instruct students to waft odors rather than inhale directly from the balloon surface.

• Why can odor molecules pass through latex while liquids remain inside the balloon?
• How does a concentration gradient drive diffusion, and what happens when equilibrium is reached?
• Which variables (balloon thickness, temperature, molecule size, solvent type) most affect diffusion rate, and why?
• What is the purpose of the unscented control balloon?
• How is this model similar to and different from diffusion across cell membranes (e.g., phospholipid bilayers, transport proteins)?