Seashell Shift Lab Activity

It’s summer and the beaches are full of explorers. As you gather sea shells, consider doing a lab activity connected to climate change and the beauty of the sea shell. The seashell shift lab is a good way to teach about chemical equilibrium and the negative impacts of climate change.

The seashell shift activity analyzes impacts of the change in pH in a water system and it’s impact on the shell of sea creatures. Within the experiment students observe a color change and see how slight changes in pH and cause for precipitate to form or dissolve. This too being an example of pH. The video below is a

Materials

3 beakers, DI water, Seashells, Sodium Bicarbonate (NaHCO3) , Vinegar, Calcium Chloride (CaCl2), and Sodium Hydroxide

Procedure

1. Place a shell in a cup and cover it with vinegar. What do you notice?

2. Make a sodium bicarbonate solution by adding one spoonful of baking soda to one cup of water. Make a separate calcium chloride solution by adding one spoonful of calcium chloride to one cup of water. Stir each solution well.
3. In a new cup, pour equivalent amounts of the NaHCO3 and CaCl2 solutions. Mix well.
4. Add small amounts of vinegar until you notice a change.
   Keep mixing the sample throughout.
5. Add small amounts of the NaOH solution until you notice
   a change. Keep mixing the sample throughout.

What Students Should Notice

After mixing the sodium bicarbonate and calcicum chloride we created calcium carbonate, and it was a fairly clear solution. Seashells are made mostly of Calcium carbonate. When pH levels drop, such as an acid being present, the calcium carbonate of the shell will break down. And form the following formula below.

CaCO3 + 2H+ –> Ca2+ + CO2 + H2O

When sodium hydroxide is aded it increases the pH and the carbonate formation. Therefore the precipitate begins the develop again. The carbon species exist in a dynamic equilibrium.

H₂CO₃ <–> HCO₃ ⁻ + H⁺ <–> CO3 ²⁻ + 2H⁺