Reaction exposed the big chill! – activity – teachengineering gas x strips directions

In the presence of water, citric acid and sodium bicarbonate (aka baking soda) react to form sodium citrate, water, and carbon dioxide. Students investigate this endothermic reaction. They test a stoichiometric version of the reaction followed by testing various perturbations on the stoichiometric version in which each reactant (citric acid, sodium bicarbonate and water) is strategically doubled or halved to create a matrix of the effect on the reaction. By analyzing the test matrix data, they determine the optimum quantities to use in their own production companies to minimize material cost and maximize carbon dioxide production. They use their test data to "scale-up" the system from a quart-sized ziplock bag to a reaction tank equal to the volume of their classroom. They collect data on reaction temperature and carbon dioxide production. More advanced students are challenged to theoretically predict the results using stoichiometry. ** We are currently working on an important update for this activity. Please contact marissa.forbes@colorado.edu for more information. **

The primary relationship to engineering featured in this activity is a demonstration of the relationships between bench scale and full scale. While the end goal may be to design a 50,000 gallon tank, the best path of discovery is to work with a smaller scale. The advantages of the smaller scale are that they 1) are less expensive and easier to operate and build, and 2) can be safer if anything unexpected happens because the surrounding environment can be controlled. The advantage of the large scale is that it directly reflects the true system, so no other testing is required in order to predict behavior.

The second engineering idea being illustrated through this activity is the engineer’s responsibility to design systems that provide the maximum product with the least cost while remaining safe. For example, in this activity the reaction is endothermic and produces a gas. A poorly designed and sized tank has the potential to cause damage to people and property if the temperature decreases to a point at which the material fails. Additionally, if the tank is sized too small for the quantity of gas being produced, a tank explosion could cause catastrophic damage.

Alternatively, this activity could be used as a means of introducing these concepts. It is also an ideal opportunity to introduce the subject material of: reactions, stoichiometry, endothermic vs. exothermic reactions, mass and mole conversions, and the ideal gas law.

To keep the workers safe, chemical engineers must control the reaction temperature and pressure so no explosions occur. So the manufacturing company makes a profit, engineers must produce the most carbon dioxide [CO 2] using the least citric acid [C 6H 😯 7].

• Sodium bicarbonate (aka baking soda). Students may be familiar with baking soda from household baking and cleaning. Baking soda works as an antacid, but would taste very bad alone. Sodium bicarbonate is also used to fight fires because at high temperature it turns to carbon dioxide and can smother fires.

• Relevance: acid + base = water + gas + salt (the product is neutral). Example applications: 1) Ant-acids neutralize stomach acid. 2) Bases used for reclaiming land used during mining (the water is very acidic and needs to be treated to be neutralized). 3) Acids and bases used to promote plant growth. Neutralizing acidic or basic soil to promote plant growth.

• Background: It is recommended to divide the class into four groups so each "engineering team" performs a different reactant ratio on Day 2. This way, the entire matrix can be tested without all students needing to perform five sets of experiments. Suggested tests:

• On the classroom board or overhead projector, prepare a large data table for all students to record their findings (from Day 2). Make it visible for the entire class and suitable to serve as a visual aid in the discussions at the end of Day 2.

For more advanced students, challenge them to first calculate how much CO 2 should be produced theoretically in each reaction using stoichiometry, before actually doing the experiment. As a bonus question, ask students: Is there any way to calculate theoretically how much carbonic acid should be produced in each experiment? At the end of the experiment, have students compare their theoretical to actual answers. Ask them to explain why their experimental results will probably never be the same as theoretical results. (Possible answers: Perhaps not all CO 2 produced will be collected; perhaps not all of the limiting reactant will react to produce the theoretical product quantities.) Refer to the Theoretical Results Using Stoichiometry Solution Guide .

This content was developed by the Culturally Relevant Engineering Application in Mathematics (CREAM) Program in the Engineering Education Research Center, College of Engineering and Architecture at Washington State University under National Science Foundation GK-12 grant no. DGE 0538652. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.