Investigation: Plop Plop Fizz Fizz


Do you remember the old commercials from Alka-Seltzer? You probably remember catchy jingle: “Plop plop fiz fiz …. oh what a relief it is!”

Your young students probably won’t remember the commercial, but this lab can be fun. Students observe tablets dissolving in water. They release bubbles as they dissolve in the chemical reaction. The tablets are made with sodium bicarbonate (baking soda) and citric acid.

Sodium bicarbonate reacts spontaneously with acids, releasing CO2 gas as a reaction product. The bubbles you see are carbon dioxide. In the stomach, the sodium bicarbonate will neutralize stomach acids.

This lab explores variables that would make the tablet dissolve faster. Students place the tablets in warm or cold water, vinegar, and salt water. They record the time it takes for the tablet to dissolve. You can speed this lab up if you break tablets into halves (this saves money too!). You could also substitute with other dissolving materials, like sugar cubes or candies. Test first! Some candies are coated in material that slows down how fast they dissolve.

If you’re not afraid they might inject it, you could also use laundry detergent pods. If you’ve never watched one dissolve, check out this video. The colors are fun!

Introduction to the Scientific Method

This lab works well with introductory units on the scientific method. Students must develop a hypothesis, collect data, and draw conclusions. The results are often mixed, with students having a wide range of observations. This can lead to good discussions on experimental errors and reproducibility.

A data table is included that for students to complete and a final question asks students to write in a complete sentence, what happened in the experiment and specify which variables affect the speed the tablet dissolves.

This lab is intended for beginners. Students can easily follow the instructions and collect data.   Plus, the experiment doesn’t take very long and doesn’t require a lot of prep.

Advanced students explore the scientific method and surface tension.

Grade Level:  6-9  | Time Required 35-45 min