Choose a Mixing Exhibit for the Lemur Learning Porch

A Visitor Exhibit Under Review

The zoo's Lemur Learning Porch is preparing a family science exhibit. Visitors will investigate whether mixing materials can produce a new substance. Before choosing a demonstration, the student exhibit team compares several mixtures. Their challenge is to show convincing evidence, not simply an interesting change in appearance.

An educator supervises the tests at a visitor worktable, away from animal food and habitats. Everyone wears safety goggles. The team uses small amounts of household vinegar, baking soda, table salt, and room-temperature water. They do not taste the materials, touch the mixtures, or close the cups.

First, the team labels matching clear cups A and B. They put 20 milliliters of water in A and 20 milliliters of vinegar in B. They add 1 gram of baking soda to each cup. They stir each mixture for five seconds with separate, matching spoons. The liquid type is different; the amounts, cups, stirring time, and starting temperature are the same.

Cup A becomes cloudy, with some white material near the bottom. A few bubbles appear during stirring, then quickly disappear. Cup B produces streams of bubbles that rise through the liquid and escape at the surface. These bubbles continue after the team stops stirring. The team also stirs vinegar without baking soda. Its few stirring bubbles stop when stirring ends.

The team repeats the A and B tests three times, using fresh materials and clean cups. In each round, they start a timer when stirring ends. They measure how long bubbling continues. They record zero seconds when no bubbling continues after stirring. The graph in the next section shows their results.

For another comparison, they stir 1 gram of salt into 20 milliliters of water. The salt grains disappear from view, and the liquid stays clear. No continuing bubbles appear. The team records what they see without deciding that a material is gone just because it is no longer visible. Their exhibit will need observations that help distinguish a new substance from a different-looking mixture.