The phenomenon is the oxidation of steel wool in a closed system. The mass of steel wool remains unchanged as it oxidizes. In this demonstration, a piece of steel wool is placed in a flask, covered by a balloon and massed. Students observe the system 30-45 minutes later, and find the steel wool has changed color, the balloon has been sucked into the flask, and the mass has remained constant.
- Resource Copyright Owner: University of Virginia Physics Department
- Type of Resource: text/plain
The resource addresses the actual substance of the learning goal rather than
just the topic.
This discrepant event stimulates thinking about the way in which substances are interacting, as it focuses students on coming up with an explanation for the conservation of mass. How can mass be conserved if a substance was "created?"
The resource addresses the entire learning goal.
The resource correctly reflects the level of sophistication of the learning
The resource provides an example of the conservation of matter that can be explained in terms of substances (atoms) interacting and rearranging as opposed to being "lost" or "created."
Please note the resource includes details on balancing chemical equations which is a higher level of sophistication than the learning goal.
Notes for Teachers
Quality of instructional support
Is the relationship between the phenomenon and the learning goal made clear?
Yes—The relationship between the phenomenon and the learning goal is made clear.
The phenomenon supports the idea that during the chemical reaction of steel wool with oxygen in the closed flask, the mass does not change.
Is the phenomenon likely to be comprehensible to students?
Yes—The phenomenon is likely to be comprehensible to students.
The phenomenon is likely to be comprehensible to students provided the topic of balancing chemical equations is eliminated.
Is the phenomenon first-hand (when appropriate or practical) or
vicarious through use of video, pictures, or text?
Yes—The phenomenon is first-hand (when appropriate or practical) or vicarious through use of video, pictures, or text.
The inversion of the balloon on top of the closed flask is a concrete observation that supports the involvement of a component of air reacting with the steel wool.
Is the phenomenon efficient, i.e., the benefits justify the costs in time and money?
Partial—The phenomenon is somewhat efficient: the benefits may justify the costs in time and money.
The demonstration uses readily available materials: vinegar to remove the protective coating on the steel wool, steel wool, balloons, and flasks.
The remaining activities described in the resource use four chemical solutions that may be difficult for some districts to obtain or are prohibited. Caution should be used as some of these chemicals are very caustic.
Useful with modification
Notes to teachers
Instead of balancing this chemical equation as suggested in the teacher notes, "account for all of the atoms" to help students recognize why mass is conserved at the particulate level through modeling the rearrangement of available parts. For example, red balls could be used to represent the iron atoms present in the steel wool, while yellow balls could be used to represent the oxygen atoms present in the air in the balloon. This also would help students who are struggling to understand why the balloon eventually gets sucked into the flask.
Explain the role of vinegar in this activity as a cleaning agent that is not involved in the chemical reaction.
Have students perform the activity involving steel wool only. The chemicals used in the later portion of the activity are highly caustic and unnecessary. If proceeding with this lab as written, students need to be alerted to the dangers and proper laboratory safety precautions should be followed (ex: eye protection, aprons, gloves, etc.)
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