Properties and Changes of Properties in Matter
Sat, Dec 15, 2012 11:47 AM
This SciGuide is about the properties of matter (both chemical and physical), and how those properties can change. I enjoy this SciGuide because it includes a lot of activities that expressly addresses density which is a profoundly important concept when dealing with ocean chemistry: hot liquids (which are less dense) can contain more dissolved gases (like carbon dioxide, which plays a significant role in ocean acidification), cold liquids (which is more dense) contains more nutrients. Moreover, density lays the foundation for how convection currents work in the mantle as well as wind and ocean currents. It was its focus on density that drew me to it, I especially like the layered salt-water column in a straw activity. However, I’m not too big of a fan of the old :density of differently sized objects of different masses” activity that it has. Outside of being the standard go-to to teach density, my biggest problem with this is that it doesn’t really get to the fundamental concepts of how density works with matter. It stays at the surface Size = volume. Mass = grams of an object. That’s true, but what about fluids, which can have more matter stuffed into a given volume. Matter you can’t see, and isn’t expressly obvious as a steel ball versus a lead one. It also annoys me that it ignores how volume of an object changes based on its temperature which in turn changes its density. This is the very reason why water is so precious to life on Earth. However, this SciGuide did convince me that I should include density as part of my instruction.
The water column in a straw is a wonderful activity, though. It helps students realize that density of a liquid can change when material is added to the liquid (like salt). The volume of the liquid changes when temperature is change, thus resulting in a changed density (my own addition to the experiment). Another key chemical connection, is that dissolving salt in water is possible because both are polar compounds. But, water can only hold so much, which leads to supersaturation, crystal formation, metamorphic rocks, and sedimentary rocks.
The other activities are simply outstanding and should be included in any middle school science class just out of principle. They provide concrete experiences for key concepts that any student should understand regardless of their future plans.