Does It All Add Up?
Dana Damm, Henning High School, Henning MN 56551
Initial Publication Date: September 15, 2009
Summary
In this chemistry classroom lab activity, students will be exploring the molecular properties of different substances. The lab is structured to surprise the students and encourage critical thinking. The main focus of the activity is for them to add a volume of 10ml of rubbing alcohol with 10ml of DI water. The traditional student will expect these volumes to add up to 20 ml. However, due to the molecular structure of each substance, the volume will be less than 20ml. It will be around 19 ml. Imagine putting rocks into a jar and then pouring sand in around them. The sand works its way into the gaps made by the larger rocks. This is the same principle as the lab in focus here. The smaller alcohol fits into the gaps made by the larger water molecules.
Topics
Bonding & Molecules
Grade Level
High School (9-12)
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This lab focuses on inquiry, critical thinking, making measurements, and understanding the "unseen" world of science. It teaches students that it is important to think critically instead of jumping to their first conclusion. It teaches students to make careful measurements and most importantly, it challenges them to think and argue amongst themselves.
Context for Use
This lab can easily be accomplished in a 50 minute period. This works well as an introductory lab to get students thinking. It requires little previous knowledge. This activity would work well for any age group over 7th grade. The only hazard would be working with the rubbing alcohol as well as the glass graduated cylinders.
Description and Teaching Materials
I use this lab as in introductory activity for my chemistry course. The materials necessary are : DI water, rubbing alcohol, graduated cylinders, goggles, aprons, gloves, and lab report material. I have found that this activity is an easy inquiry project. It is easy enough to allow for me to help them ease back into the school year and become familiar with lab procedures. The activity is adopted from a demonstration presented in my teacher's edition of Holt Chemistry.
Teaching Notes and Tips
One obstacle with this lab is if the student actually gets 20.0ml due to sloppy measurements on their part. Should this occur, it is necessary to give the student guidance and assistance as they re-measure their volumes and attempt the lab again.
Assessment
I have not actually attempted this lab yet. However, it is structured in such a way that there is very little room for error. The lab should serve as an informal way to begin the school year and introduce very basic lab techniques. The student will submit their lab handout with the answers written on that page. However, one could take this a step further and ask the students to create a formal lab report. I have chosen not to do this due to the lack of quantitative data.
Standards
Strand II. A. Structure of Matter: The student will understand the nature of matter including its forms, properties, and interactions.
References and Resources