The Balloon Valve Test at Riverbend Bike Co-op

A Safe Inflation Model

The Riverbend Bike Co-op runs a science table during a community repair night. The team wants to investigate whether mixing substances can make a new substance. They do not connect anything to a bicycle. Instead, they use small plastic bottles and balloons as a safe model for noticing a gas. An adult measures 40 milliliters of warm water into each bottle. The water is warm, not hot.

The written model diagram shows four bottles. Bottle A contains warm water, one teaspoon of dry yeast, and one teaspoon of sugar. Bottle B contains warm water and yeast. Bottle C contains warm water and sugar. Bottle D contains warm water and salt. A balloon is fitted over each bottle opening. The team uses the same bottle size, water amount, balloon type, and room location for every bottle. They gently swirl each bottle for 10 seconds.

At 5, 10, and 15 minutes, the team measures each balloon's circumference. A circumference of 0 means the balloon is not expanded. The team repeats the setup three times with fresh materials. The results are shown below.

Balloon circumference after 15 minutes (cm): Bottle A: Trial 1 = 8, Trial 2 = 7, Trial 3 = 9. Bottle B: Trial 1 = 0, Trial 2 = 0, Trial 3 = 1. Bottle C: Trial 1 = 0, Trial 2 = 0, Trial 3 = 0. Bottle D: Trial 1 = 0, Trial 2 = 0, Trial 3 = 0.

Additional observations: Bottle A had bubbles and foam inside the bottle. Bottle B's liquid stayed cloudy from the yeast, but the balloon stayed nearly flat. Bottle C's sugar grains disappeared into the water, and the balloon stayed flat. Bottle D's salt grains disappeared into the water, and white grains appeared again after some water evaporated.