That darned week before winter break! After the semester final is given, what do you do to keep the student's attention?
About 8 years ago I started undertaking several "holiday labs" that were designed to keep students involved in chemistry-related activities while also celebrating the season. These are some of the top labs that have become a custom at our school. They are very popular; students look forward to them all year.
Economics are tight. The first few years that I did these labs I poured a significant amount of my own money into them. Looking back, I could have saved a lot if I had known some of the tips discussed below. I have routinely offered the labs as "optional", even though just about all of the students jump on board. I collect $5.00 per student in lab fee - this covers the cost of the majority of materials and provides the students with some nice home-made gifts to give family or friends. I start collecting the week before Thanksgiving break. This gives me some time to start ordering the materials early without draining my bank account too badly.
If you are a teacher just starting out, you may want to do just one of the labs, and add one each year. This will give you some valuable time to ease into the process and prevent you from going mad.
Doing these labs with other teachers can either be a blessing or a curse. If you work with people who are helpfull and willing to take on shared responsibilities - go for it. I find this is the majority of educators, and It makes for a wonderful experience for students, teachers, and the whole department. However, experience has taught me that there are some teachers who will sieze the opportunity to "unload" their students onto you for these labs, especially since you "already have everything set up."
After many years of trial and error using both glass and plastic bottles, I have determined that the best results are obtained with plastic jars. I order them from one of several online supply warehouses. Last year I had very good results using 16 oz PET jars like these or these . It is important that the jars don't leak, so get lined lids.
-plastic or glass jar
-hot plate
-small figurine to go in the jar
-hot glue gun & glue
-optional: silicon sealant for jar lid
Benzoic acid is readily available from many of the science supply warehouses, including Flinn, Carolina, Sargent-Welch, etc. It is even available on EBay, as are a lot of different chemicals.
The amount of benzoic acid that you will need will depend on the number of students and the size of the jars. Benzoic acid has a solubility of 0.28g/100 mL at 20 deg C
and 6.9g/100 mL at 90 deg C. I usually use about 1.6g/100 mL to get a pretty good amount of snow. This means for a class of 30 students, using 16 oz jars, you would need about 230g of benzoic acid.
Depending on your student load, you may wish to use smaller jars. Adjust the amounts accordingly, using the conversions of 1 oz = 30 mL, and about 16 g benzoic acid per liter of solution.
If you teach high school or college, you may want your students to mix their own solution. The water must be heated to about 90 deg C prior to adding the benzoic acid. DO NOT BOIL the solution, as this may affect crystallization (I have not researched why yet, but boiling can prevent crystallization).
The student needs to hot glue their figurine or other item to the inside of the lid prior to adding the solution. The item must not impede the closing or sealing of the lid.
There are always some students that want to put a picture in their snow globe. I happen to have a laminator in my room, and this has worked well for photos. It is important that the picture is small enough to fit in the jar AFTER LAMINATION. In other words, there will be about 1/4 inch around the picture that is required for sealing the lamination. If the student cuts the lamination too close to the picture, the solution will seep in and wreck the picture. You can purchase a laminator for about $30 at Costco or an office supply store. Lamination sheets run about $20 for a pack of 100; a lot less at Costco or Sam's Club.
When it is time to add the solution, it is important to wait for the solution to cool before screwing on the lid. This is because the hot glue will melt if placed into the hot solution. I pour the solution in for the student, leaving the jar not quite full. After it cools, they can top the jar off with cold water before screwing on the lid. If there are any leaks, the student can apply a small amount of silicon sealant to the jar. However, this is usually not necessary if you buy lined lids.
4hot plate
Concept : solutions, solubility, crystallization
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