1.1: Carbon Fizz
How can I monitor and model the movement of carbon in a system?
Carbon: It is vital for life. In your body, carbon makes up about 50 percent of your tissues and about 28 percent of your bones. In plants, carbon forms roughly half of tissues.
Carbon is also a natural part of the air that you breathe. Maybe you have learned about photosynthesis in science. Photosynthesis transfers carbon from the air to plants or other photosynthesizing organisms that are growing. As you can see, carbon connects to life in many ways.
Carbon is also a key part of non-living systems (abiotic), such as minerals like diamond or graphite. It is found in rocks, too, including limestone and rocks with fossil fuels, such as petroleum, coal, and natural gas. These are forms of carbon that you use and rely on.
Think about this: How might you describe carbon to a friend who was not in your science class? Would you describe a color for carbon? How many forms of carbon can you think of? How does carbon relate to your energy needs? Carbon Connections will help you answer questions like these. You will start thinking about carbon and how it moves around Earth.
In this lesson, you will learn that:
For Lesson 1.1, consider the focus question. It will help to guide your thinking about how carbon moves in the Earth system. This question, along with two experiments, will help you model carbon in the Earth system.
Start with this investigation to simulate the movement of carbon in a system. Have you heard of dry ice? It's a solid form of carbon dioxide (CO2), just as ice is the solid form of water (H2O). CO2 must be much colder than ice to be a solid, however. Also, CO2 does not melt to a liquid and become "wet" like water. It changes from solid CO2 directly to CO2 gas. That is why it's "dry."
Dry ice is a good source of CO2 for science class. Your goal is to monitor and observe how CO2 gas interacts with water. How will you be able to tell if the CO2 is interacting with the water? To do this, you will use a chemical indicator that changes the color of water as carbon moves in the system. Do the following steps to investigate this process.
You may wonder why CO2 makes water change color. Watch the Carbon In time lapse video of this reaction. The reaction takes approximately one hour in real time. This relates to some very important reactions. These reactions are a key part of all marine and aquatic systems. You can learn some more details about the reaction by clicking on Explore More: Carbon Indicators—Responding to Reactions.
Carbon Indicators—Responding to Reactions
You may think that science is about measuring values, or getting the "answer." While that can be a part of science, indicators—in science or any other field — can tell you important things about systems. Besides giving you values, indicators tell you whether something has changed, and whether it's changed by a lot or just a little.
You used bromthymol blue (BTB) as an indicator in Lesson 1.1. In your investigation, the color of the solution with BTB changed as carbon moved, but the molecule with the carbon also changed. The reactions showing those changes are in the equations below. These reactions are a fundamental part of carbon cycling in all freshwater and marine environments.
The two equations below show CO2 moving in and out of water. The subscript "aq" refers to aqueous for the substance that is dissolved in water. The subscript "gas" refers to the substance in a gas state. This CO2 is also an important part of air. You should be able to tell which reaction represents Carbon In for the air, and which one represents Carbon Out of the air. If you are not positive that you know, check with a partner.
CO2(gas) → CO2(aq)CO2(aq) → CO2(gas)
Once a CO2 molecule has entered the water, it can react with the water, H2O. A CO2 molecule can join with a water to make carbonic acid, H2CO3.
H2CO3 + H2O(l) → H2CO3(aq)
It is called an acid because of the next change. Carbonic acid in water separates (dissociates) to the ions H+ and (HCO3)-1, the bicarbonate ion. An excess of hydrogen ions (H+) leads to a solution that is acidic. The reaction is:
H2CO3(aq) → (HCO3)-1(aq) + H+1(aq)
By combining the equations, you get a full reaction sequence that connects CO2 to H+. The full reaction is:
CO2(aq) + H2O(l) ↔ H2CO3(aq) ↔ (HCO3)-1(aq) + H+1(aq)
What happens when you increase CO2 in this system? Adding more CO2 to water forces the reaction to the products in the image. This creates more H+, and the system becomes more acidic. The image shows color changes for BTB that go with that change in acidity. It also shows that H+ and color also relate to a numerical scale. This is the pH scale for the amount of H+ in solution. A change from blue to yellow for BTB indicates a change to lower values of pH.
What if you decreased CO2? The color change to green then blue indicated pH at 7, and then going slightly higher than 7. In this case, CO2 leaving the water is the reaction going to the left, with a decrease in the H+. The system then becomes more basic.
CO2(aq) + H2O(l) ← H2CO3(aq) ← (HCO3)-1(aq) + H+1(aq)
Bromthymol blue is very useful because it displays a rapid color change, right in the middle of the scale (pH=7).
In this section, you will investigate another model of carbon moving in the Earth system. Keep the model in mind as you learn more about the carbon cycle and climate in Unit 1. You will use bromthymol blue (BTB) again.
Carbon Out Activity
Materials per Team
Process and Procedure
Leave the control tightly closed. You will shake the experimental bottle only.