Hands-on Activity Reaction Exposed:
The Big Chill!

Learning Objectives

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.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• 8 g citric acid (C₆H₈O₇)
• 10.4 g sodium bicarbonate (baking soda)
• 40 ml water
• 2 quart-size ziplock bags
• thermometer (approximate range: 0-200 °F)
• syringe (approximate size 4 ml, for taking gas sample)
• tape measure
• calculator
• colored tape to seal syringe
• safety glasses, pair per student
• Exposed Reaction Worksheet

To share with the entire class:

• stopwatch
• (optional) use of GC for data analysis of CO₂ production; the production of CO₂ can also be estimated through calculations using the stoichiometric balance of the reaction equation

Worksheets and Attachments

Pre-Req Knowledge

Students should be familiar with:

• Math concepts: volumes, graphing data, measuring and unit conversion, and conservation of matter.
• Science concepts: mass, temperature measurements.

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.

Introduction/Motivation

In the presence of water, citric acid [C₆H₈O₇] and sodium bicarbonate [NaHCO₃] (aka baking soda) react to form sodium citrate [Na₃C₆H₅O₇], water, and carbon dioxide [CO₂].

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 [CO₂] using the least citric acid [C₆H₈O₇].

In groups of two, your engineering challenge is to test the reaction in the lab before a large-scale operation plant is turned on. To keep the plant employees safe and so the plant earns a profit, you must determine:

1. The temperature change that occurs during the reaction for various ratios of reactants.
2. The quantity of CO₂ produced from the reaction using the same reactant ratios.

Procedure

Background and Concepts for Teachers

1. Discuss the chemicals that will be used in the reaction. Have students discuss the physical characteristics of each.

• 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.
• Citric acid is a common ingredient in citrus-flavored foods. Have students look for it in the ingredient lists for candy and soda beverages.
• The reaction of sodium bicarbonate and water is very similar to the phenomena seen when Alka-Seltzer tablets are placed in a glass of water.

2. Discuss what a reaction is and how one might observe that a reaction is occurring.

• Demonstrate mixing citric acid + sodium bicarbonate. (Is a reaction occurring?)
• Demonstrate adding water to the mixture? (Is a reaction occurring?)
• 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.

3. Discuss the connections to engineering.

• Safety aspect: over pressure or extreme temperature can cause catastrophic failure.
• Profit aspect: using less citric acid to produce more carbon dioxide. (Is it possible?)

4. Overview of the experimental plan over the three days.

Specific Procedure

1. 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 Day 1: Everyone: 2.6 g citric acid + 2.6 g sodium bicarbonate

On Day 2:

• Group A: 1g citric acid + 2.6 g sodium bicarbonate
• Group B: 4 g citric acid + 5.2 g sodium bicarbonate
• Group C: 2 g citric acid + 5.2 g sodium bicarbonate
• Group D: 6 g citric acid + 7.8 g sodium bicarbonate

2. Before the Activity

• Collect the required reactants.
• Gather the remaining items on the Materials List.
• Make copies of the Exposed Reaction Worksheet, one per team, which includes the procedures.
• 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.

3. With the Students

Day 1: Experimental Methods

1. Present the introduction content, as described above.
2. Divide the class into groups of two students each.
3. Review the test procedures and how to use the given materials.

Day 2: Data Collection

1. Student groups conduct the same reaction using different assigned quantities of reactants.
2. Students collect, label and seal gas samples.

Day 3: Data Analysis, Discussion & Scale-up

1. Provide gas analysis results.
2. Calculate cost of reactants vs. profit from products.
3. Scale-up activity.

Vocabulary/Definitions

products: All the materials formed through a reaction. Generally "what we end up with."

reactant: Starting materials for a reaction. Generally elementally rearranged during the reaction.

Assessment

Review students' completed Exposed Reaction Worksheets to gauge their depth of comprehension.

Optional post-activity assessment: student reflection by class discussion or written assignment.

Safety Issues

• Remind students not to drink any chemicals, even those labeled water or soda, because contamination is always possible, especially in chemical laboratory settings.
• Have students wear safety goggles at all times.

Activity Scaling

For more advanced students, challenge them to first calculate how much CO₂ 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 CO₂ 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 .

Copyright

Contributors

Supporting Program

Acknowledgements

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.