Ocean Acidification

Age

Elementary School, Middle School, High School

Format

Stage Show, Hands-on

Materials

   1 beaker (2 if doing the crystallization demo)
   Water (tap is probably okay, but DI water would be best)
   Dry ice (or HCl, to reduce pH faster?)
   Eyedropper
   1 molar NaOH (optional, for crystallization demo)
   Calcium chloride (optional, for crystallization demo)
   Club soda (carbonated water) (optional, for crystallization demo) 

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. HCl is a strong acid and NaOH is a strong base - they should be handled carefully and with gloves.

Dry Ice MSDS

1M Sodium Hydroxide MSDS

Calcium Chloride MSDS

Preparation

Assemble the materials. Fill a beaker about 2/3 with water.

If doing the crystallization demo, fill another beaker about 1/2 way full with water and dissolve some calcium chloride in it.

Demonstration

Crush a few pieces of chalk and add them to the water. Now begin to add HCl with the eyedropper. You should see CO2 bubbles forming on the chalk and then floating to the surface of the water.

For the crystallization demo, using the beaker with calcium chloride, add about 1/4 of the capacity of the beaker of club soda (1/2 the amount of the water). Now begin to add NaOH until the water becomes "milky." Stop adding NaOH once the water stops getting increasingly milky.

What to Say

Corals are animals that live on the sea floor and are an important part of the Earth's ecosystem. They're not like most of the animals you think of - they plant themselves in the sand and don't move around. They can grow to form enormous reefs large enough to see from space! These reefs are terrific habitats for many species of fish, so coral reefs help support many types of ocean life. They have very strong skeletons made of calcium carbonate, the same chemical that makes an eggshell or chalk.

But coral reefs are in danger from the increased levels of carbon dioxide in the atmosphere produced by human industrial activities. To demonstrate this, I will put some chalk in this water. The chalk is calcium carbonate, just like the coral skeleton.

What happens when we add CO2? Dry ice is simply CO2, in a solid form because it is kept so cold. If I drop dry ice in the water,