Reaction Exposed: The Big Chill!
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.
An icy cold day.Copyright 2004 Microsoft Corporation, One Microsoft Way, Redmond, WA 98052-6399 USA. All rights reserved.
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.
After this activity, students should be able to:
- Follow procedures to collect data while changing more than one variable.
- Create line graphs to represent the data.
- Interpret data to predict overall behavior of multiple variables.
- Describe how this activity applies engineering design principles, including cost analysis.
Goals:
- Math competency: Skills and appreciation for data collection and analysis used in real life.
- Quantitative literacy: Ability to follow procedures and provide recommendations.
- Engineering applications: engineering design process to control products of a chemical reaction, cost considerations corresponding to performance.
- Cultural relevancy: How to follow procedures, collaborative work in small groups and hands-on activities.