CO₂ Extinguisher

Introduction & Motivation

A chemical reactor is a vessel designed to contain and facilitate chemical reactions. Materials and energy go in, useful products are created, and the mixture of product, waste, and un-reacted materials come out. This is the fundamental concept for chemical engineering. Chemical engineers design reactors to ensure that the reaction produces the most amount of desirable product while requiring the least amount of money and energy to purchase and operate. 

An important responsibility chemical engineers have is to design reactors responsibly, with the capacity to contain the reactions inside and the proper safety mechanisms, especially in cases of nuclear reactors. They also must plan how the reactor will be unloaded and reloaded in the case of batch reactors, or monitored and adjusted for continuous reactors. The goal of this experiment is to exemplify certain factors a chemical engineer must take into account when designing a reactor. 

Present this experiment as a means to solve a problem.  Carbon dioxide is a product of the below reaction. You want to put out a flame using CO₂, but how do you collect it?  How much baking soda and vinegar do you add you create the most about of CO₂ without popping the balloon?  Have the students design and build “reactors” for the reaction to take place while collecting CO₂ so that it could be transported and used to put out a small flame.

Reaction: NaHCO₃ (s) + CH₃COOH (l) → CO₂ (g) + H₂O (l) + Na⁺ (aq) + CH₃COO^– (aq)

Chemical Safety:

1. Vinegar and Baking Soda

Materials

• 2-liter plastic bottles
• Medium size plastic bottles
• Small plastic bottles
• Cups
• Plastic bags (different sizes)
• Duct tape, scotch tape, masking tape
• Funnels
• Balloons
• Tubing
• Straws
• Rubber bands
• Turkey Baster
• Baking soda (NaHCO₃)
• Vinegar (CH₃COOH)

Procedure

Before the activity, have students watch this video detailing the events of Chernobyl. Emphasize that chemical engineers work with very complex subjects which offer incredible solutions to problems, but also present sizable dangers. That being the case, they have a lot of responsibility to take their studies seriously and critically think about how to make sure every process is as safe as possible. Thankfully, there are many ways chemical engineers are trained to include safety and support from many different areas to keep everyone safe. When we become engineers of any field or study, we seriously promise we’ll do our best to be up to date with hazards and how to handle them.

1. Create two stations, one where students use a funnel with baking soda and one where they use a different funnel to with vinegar. (You may create more than just one set of these two stations to save time and make sure the students don’t get too impatient)
   
2. Have the students brainstorm ideas for their reactors.  Make sure to mention that their reactors shouldn’t just consist of mixing baking soda and vinegar in a cup and then covering the cup with a plastic bag; you want to collect the most and purest form of CO₂ possible and be able to transport it.  Try to create a closed system that both the baking soda and vinegar are present and then something is done to trigger the reaction without opening the system up.
   
3. After building the reactors, have students add equal amounts of vinegar and baking soda. Be sure to have them record the amounts and reflect on what happened. Did it seem successful? How fast did the gas-trapping mechanism inflate, if it did? Is there a better way to do it?
   
   This is a great problem solving activity! Let the students experiment with different amounts of baking powder and baking soda. Emphasize that the amount of reactants don’t only affect the amount of product, but also how fast the reaction takes place. 

**Do not exceed 1 cup baking soda and 1 cup vinegar, the balloon will pop!**

Ideal setup:

1. Use a funnel to add baking soda to the inside of a balloon.
2. Use a different funnel to fill a plastic bottle with vinegar.
3. Attach the balloon to the mouth of the plastic bottle making sure to keep the baking soda filled portion of the balloon to the side.
4. Lift the balloon upright so the baking soda falls into the vinegar and causes the reaction. 
5. Take the balloon off of the lip of the bottle and pinch or tie it up to preserve it/easily dispense CO₂

Discussion

1. Why do you think that the balloon inflated faster as we added more vinegar and baking soda? (More reactants, more surface area for the reaction to occur)
2. Make a point to bring up batch versus continuous reactors.  Point out which the students did and what the benefits of each are.
   • Batch: involves the processing of bulk material in batches through each step of the desired process. Processing of subsequent batches must wait until the current batch is finished. This method seems effective at first glance, but in most cases falls short of continuous flow in terms of product output and time it requires to load, react, unload, and clean the reactor.
   • Continuous flow: involves moving one work unit at a time between each step of the process with no breaks in time, sequence, substance or extent.
3. What could this specific reactor be used for? Remember, CO₂ is the only gas product (i.e the gas collected is pure CO₂!) (Plant tanks, pressurizing soda, turned into solid form (dry ice), used to put out fires, etc.)
4. Can you think of another very common process that transforms a liquid to a gas? (Boiling water: not a chemical reaction, but a phase change. The vapor is still water but in gas form, so it’s not a chemical reaction. Connect to earlier activity: when monomers become polymers)
5. Reactions with gasses are some of the hardest to control and make safe. If a nuclear power plant uses water as their coolant (which turns to a gas when heated) for their nuclear reactor, why do you think it’s so important to have backup emergency cooling mechanisms?
   
   Note: nuclear reactions are exothermic, meaning they give off lots of heat!
   
   (If the cooling system fails, the water will be turned into steam which will then be continuously heated as the reactor continues to operate which can lead to reactor failure, notably the explosion of radioactive material. Connect to Chernobyl video and emphasize that in chemical engineering, safety is the highest priority!)