Summary

In this lesson, students will review the characteristics of chemical changes and then use a catalyst and an inhibitor to explore the reaction rate of the oxidation of iron.

Grade Level

Middle School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
• Scientific and Engineering Practices:
  • Asking Questions and Defining Problems
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions
  • Engaging in Argument from Evidence
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this lesson, students should be able to:

• Identify evidence of chemical reactions as indicated by the formation of a new substance.
• Explain how specific variables may impact the rate of a reaction.
• Demonstrate safe practices during laboratory investigations.
• Design and conduct an investigation to understand ways in which reaction rates can be controlled.
• Organize data, identify patterns, and analyze investigation results.

Chemistry Topics

This lesson supports students’ understanding of:

• Chemical Reactions
• Chemical Change
• Reaction Rates
• Catalyst
• Inhibitor

Time

Teacher Preparation:

• Day 1: 40 minutes (to test the materials to ensure rusting will occur)
• Day 2: 20 minutes (to review students’ lab procedures)
• Day 3: 10 minutes

Lesson: Three 40-minute class periods

Materials

• Disposable handwarmer (for demonstration – the Hot Hands brand works well)
• Aprons
• Goggles
• Vinegar (enough to submerge the steel wool)
• Beakers (1 per group – for soaking steel wool in vinegar)
• Steel wool (1 small ball per group – steel wool without soap works best and I have had the greatest success with steel wool from the dollar store)
• Water (for soaking and rinsing the steel wool)
• Plastic baggies (1 per group)
• Gloves (depending on the type of steel wool used, students may need to wear gloves to avoid getting cut by the wool)
• Various food grade liquids (Examples: Carbonated waters, carbonated beverages, electrolyte drinks, corn oil)
  • These will serve as available options for students for the experiment portion of the lesson 
  • Note: Do not try cleaning solutions or other chemicals that may be hazardous to students for the experiment portion of the lesson
•  Optional: Thermometer (to measure the temperature change of the steel wool)
• Optional: Salt (students may want to add this to their water)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals. Solid materials can be placed in the trash while liquids should be flushed down the sink with ample amounts of water.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Gloves should be worn if handling steel wool.
• SDS for vinegar
• SDS for steel wool

Teacher Notes

Day 1

• Prior to this lesson students should understand the difference between physical change and chemical change as well as the indicators of a chemical change.
• The teacher should begin the lesson by completing a demonstration of a chemical reaction or showing a video of a chemical reaction. Elephant toothpaste is a good example and this video shows a quick example. The AACT website has instructions for the demonstration.
• After viewing the video or demonstration, the teacher will ask the students to complete the “Activating Prior Knowledge” section of the student handout. This begins with recording observations from the demonstrations and identifying characteristics of chemical change. Students should identify the formation of a gas and production of heat (observed as the steam rising from the foam).
• The teacher will ask students to list other characteristics of a chemical change. The teacher can make note of these characteristics on chart paper or the board. These characteristics may include unpredictable change in color, unpredictable change in temperature, production of gas, formation of a precipitate, production of an odor.
• The teacher will then ask the students to brainstorm a list of every day chemical reactions.
• After allowing time for students to brainstorm individually, the teacher will ask the students to share their ideas and create a class list of chemical reactions. Students may identify cooking, baking, and combustion as examples of chemical reactions. They may also list examples such as baking soda and vinegar, digestion, and photosynthesis.
• Upon generating a list, the teacher will ask the students if the chemical reactions happen quickly or slowly. The class could also place the reactions in order from perceived rate of reaction.
• The teacher will explain that some reactions happen quickly while other reactions may happen slowly.
• The teacher will ask the students to give examples of when it might be helpful to speed up a reaction and when it would be helpful to slow down a reaction. Once students have had a chance to think about their responses, the teacher will ask for volunteers to share their ideas. Examples of reactions that need to happen quickly are the inflation of an airbag or the dissolving of an antacid. Examples of controlling reactions that happen more slowly are photosynthesis and the decomposition of food. It is important to remind students that some reactions take a very long time to occur.
• The teacher will explain that sometimes a catalyst is used to help a reaction happen more quickly.
• The teacher will also explain that an inhibitor can be used to prevent or slow the rate of a reaction.
• The teacher will explain that the students will be exploring a specific type of reaction, an oxidation reaction also known as rusting. This ACS Reactions video can be used to help students understand why objects rust.
• The teacher will ask the students to share examples of items that form rust. Students may share examples such as cars, bicycles, and other metal objects.
• The teacher will ask students if rusting is a slow reaction or a fast reaction. The teacher will explain that they will be exploring rusting and how to speed up or slow down the process.
• The teacher will then take out a disposable hand warmer and explain that it is also an example of a chemical reaction that causes rust. Students will complete the questions on the student handout under the heading, “Rusting Demonstration 1”.
• The teacher will ask the students to review the ingredients of the handwarmer – iron, cellulose, activated carbon, water, salt, and vermiculite.
• The teacher will then ask the students to explain why the handwarmer is not hot while it is in plastic but gets warm when it is out of plastic. The teacher will then explain that oxygen is required for the chemical reaction to occur and that the plastic barrier is serving as an inhibitor (delays, slows, or prevents the reaction) because it keeps oxygen from reacting with the iron.
• The teacher will explain that when oxygen combines with the water and iron, the rusting process begins. In this reaction, salt is a catalyst that speeds up the rusting process, so heat can be generated more quickly. 
• The teacher may also make the connection that cars in the Salt Belt rust more quickly than cars in other locations because salt is used on the roads in the winter and this salt expedites the production of rust.
• Additional information about the chemistry of disposable hand warmers may be helpful to review as well.
• The teacher will then explain that rust is a process that people have tried to speed up and slow down, for various purposes.
• As a conclusion to the first part of the lesson, the teacher will ask the students to list three items that can rust and try to determine if it would be helpful for the rusting process to speed up or slow down on those items.

Day 2

• Before class begins the teacher should begin soaking a ball of steel wool in vinegar. This is done by putting the steel wool in a glass or beaker and pouring vinegar into the glass/beaker until the steel wool is covered. The steel wool should soak for about 20 minutes prior to being removed.
• The picture to the right shows a sample of steel wool that is used for cleaning dishes. The steel wool at the top was not placed in vinegar while the steel wool on the bottom was placed in vinegar for 20 minutes and then placed in a baggie.
• The teacher will ask the students to share their examples of items that rust and make a list on the board. Possible student answers include items such as bicycles, automobiles, buildings, etc. The teacher will explain that while all these items can rust, it is difficult to experiment on them.
• The teacher will briefly review the information from the previous day by recapping the characteristics of a chemical change.
• The teacher will ask the students to list the characteristics that they will look for in the rusting process. Students should identify that they could look for a color change and a temperature change.
• The teacher will then show the students a ball of steel wool and explain that, like the iron in the hand warmer, steel wool also contains iron so it can go through an oxidation reaction too.
• The teacher will tell the students that they will be exploring the rusting of steel wool. Students should record observations on the student handout in the section, “Rusting Demonstration 2”.
• The teacher will ask the students to think about what might be required for the steel wool to go through an oxidation reaction.
• The teacher will remove the steel wool from its packaging and ask the students to observe it. The teacher will ask the students why it isn’t getting warmer or rusting the way the handwarmer did when it was removed from the packaging. The students may identify that while oxygen is present, water is not.
• The teacher will then show the students the steel wool in the vinegar beaker.
• The teacher will remove the steel wool, dry it off, and place it into a plastic baggie. If temperature is being measured, a thermometer should be placed in the baggie and touching the steel wool. If possible, wrap the steel wool around the thermometer.
• The class will observe the rusting process as the temperature of the bag increases (the bag may become cloudy) and the steel wool begins to change color. This process should occur 5-10 minutes after placing the steel wool in the baggie.
• If desired, the teacher could have small groups of students complete this activity rather than conducting it as a demonstration. Each group would need a ball of steel wool, a cup/beaker, vinegar (enough to cover the steel wool), paper towels, and a baggie. The group would place the steel wool into the cup/beaker and pour vinegar over it. The steel wool would sit for 20 minutes and would then be removed, patted dry, and placed into the baggie. A thermometer could be placed in the baggie to demonstrate the change in temperature.
• The teacher will explain that the steel wool has a coating on it that acts as an inhibitor (which slows down the oxidation reaction). The vinegar reacts with the coating to remove it. The vinegar also contains water, so once the steel wool is removed from the vinegar and placed into the baggie it has access to oxygen and has been exposed to water through the vinegar, so the rusting process can take place.
• After the demonstration, the teacher will ask the students to think about other common liquids that may be used to cause the steel wool to rust or prevent the steel wool from rusting.
• The teacher will place the students into small groups and ask the groups to use the lab template to design an experiment. This can be found in the “Rusting Experiment” section of the student handout.
• The teacher will work with the class to set the controls for the experiment, such as the amount of liquid, the amount/type of steel wool, etc. Vinegar should not be used in this experiment. Liquids such as water, salt water, vegetable oil, and carbonated beverages could be used. Water and salt water will produce rust. Sodas, such as Sprite, and vegetable oil won’t cause rust.
• Students experiment ideas should be built around their previous experiences that in order to rust, the steel wool needs to be in contact with water and oxygen. Students should be encouraged to review the ingredients of the items they choose to use in their experiment.
• It is recommended that the experiment be started early in the week as it may take a couple of days for rusting to occur, depending on the type of steel wool used.
• Experiment variations could include leaving the steel wool partially submerged in the liquid, so the steel wool has access to oxygen and the liquid or students can submerge the steel wool in the liquid for 20 minutes and then place the steel wool in a plastic baggie.

Day 3

• Prior to conducting the experiment, the teacher needs to have reviewed all of the students’ experiment ideas for safety and address any potential concerns.
• The students should put on the proper safety gear and set up their experiment.

Day 4 (Optional/if needed)

• The students should check on their experiments each day, recording data as necessary.
• When the teacher has identified that rusting has taken place, the experiment should come to an end. Students should record their data and clean up their workstations.
• The teacher should lead a debrief of the activity by having the groups of students share out their findings with the class. As a class the students should determine which substances caused an oxidation reaction and why.

Results

• An Answer Key document is available for teacher reference and includes photographs of expected results.