Creating and Destroying Limestone
Demonstration
The whole lab can be demonstrated in a short amount of time. This is an "eye-opener" for most students when they witness that the tiny amount of CO2 can, and does affect, the test-tube marine environment.
Abstract
Students pour 2 cm of limewater into a test tube. Using straws they blow into the limewater making a calcite precipitate (Part 1). After discussion, they repeat the process and the calcite disappears (Part 2).
Faculty led discussion is a key component.
Part 1. What happened and why? What are you adding to the limewater? Where is the CO2 coming from? Where is the C coming from? What is a precipitate? How are limestone, chalk, and calcite shells formed?
Part 2. What are you still adding to the limewater? Why did the calcite dissolve?
Connections and Additions.
Human, plant life, and photosynthesis at many levels. Most students do not know where or how the C is added to CO2. Relevance to climate change, acid rain and limestone dissolution. How CO2 in the atmosphere affects the ocean and causes ocean acidification. How will this affect shells, corals, crabs? The chemistry, including formulae can be added at many levels, and discussions of pH, acids and bases.
Outcome: Students can visualize and articulate a complex sequence of chemical reactions that have a profound effect on the current world environments. Students can extrapolate what they see today into past ecosystems (fossils and sedimentary processes).
Context
Discussion can be adapted to any target audience from middle school to college level. This exercise can be used in classes on paleontology and climate change, and in sedimentology and mineralogy. It has also been successfully used in a STEM camp for middle school girls.
It is a way of enabling the students to think about what is happening in their environment today. Many students know of the term "climate change" but not ocean acidification. They are surprised CO2 in the atmosphere can affect marine life. The activity builds connections and relevance.
Why It Works
It is effective and innovative because the students actually cause a significant change with just a little CO2. They then make connections between seemingly disparate pieces of information that they have been taught, but do not usually connect. It is surprising how many students do not know why they breath out CO2, or can rationalize where the C comes from.
This lab can be used over a wide range of disciplines. It is safe, easy to do, and visible results can be achieved quickly.