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Name: Martha
Status: educator
Grade: 6-8
Location: MD
Country: USA
Date: Summer 2011


Question:
I can demonstrate to students that water expands when it freezes, by putting water in a glass jar, marking the volume, freezing it, etc. My question is this: Is there a liquid (readily available, freezable with a normal freezer) that I could use to demonstrate that substances other than water are more dense in the solid than the liquid form? (I would like to be able to show that the substance "shrinks" when frozen.)



Replies:
This is easy to demonstrate, and you do not even need a freezer. All you need is a small package of ordinary paraffin wax, used for sealing jars of home made jams, jellies etc. It is usually sold at larger grocery stores.

Paraffin wax usually freezes (depending on the exact type) at around 60°C to 80°C. Heating it over a pot of boiling water will melt it, then when you remove it from the heat, it will gradually "freeze" to a solid as it cools, and in doing so, it will very visibly shrink.

Regards,

Bob Wilson.


Martha,

Water is actually the exception here in that it is less dense (larger) in the solid form than in the liquid form. Almost every other liquid will be the other way with the liquid taking up more volume than the solid. Anything not water based will likely work though the larger the difference in the density the larger the change will be that you see. Two demonstrations we do here are vegetable oil (where 5 mL in a 10 mL grad. cylinder with shrink to about 4 mL) and wax. For the wax example we heat it until a liquid and then pour into a test tube. As it cools you can see it shrink and voids form in the solid.

Brad Sieve


There are other substances that expand when frozen, but I don't know of any simple, cheap candidates.

vince Calder


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