Chemicals are cool... especially this one!

Posted: Sat Jun 19, 2004 5:18 am

WATER!

“Water?” you say, with an eyebrow raised and a skeptical tone in your voice. “Water is very pretty, but pretty is NOT the same as cool.”

Water is cool for LOTS of reasons:
1) When H2O is solid (ice), it is less dense than when it is liquid (water); ice cubes and icebergs float. This simple but important fact is a requirement for life in lakes, rivers and streams, and in oceans at the poles. (If ice suddenly started sinking in water, the global climate would also be seriously disrupted. Polar oceans would freeze from the bottom up.)
2) Water is a requirement for life on this planet.
3) Water molecules like to stick together (cohesion):
4) Water molecules like to spread apart (adhesion): watch food-coloring in water climb up a carnation or celery stalk. Tall trees can take advantage of this property of water. By evaporating water from their leaves, the water gets sucked up from the roots. Because water clings to itself, a column of water gets sucked up the tree. (If you’re trying to impress that special someone in your life, call it “transpiration”.)
5) Water has an extraordinary ability to dissolve substances.
The list of water’s cool-ness goes on.

Many of water’s cool properties come from its funny Mickey-Mouse shape.

The oxygen (O) end of the water molecule has a slight negative charge (which means is slightly attracted to things with positive charges), and the hydrogen (H) ends are slightly positively charged (which means they are slightly attracted to things with negative charges). So, even though water sticks together, it will also attract or be attracted to other chemicals. The small difference in electrical charge allows water to work its way around other molecules…this will make those molecules dissolved into the water. For this reason, was has sometimes been called the “universal solvent”. There are lots of websites with more information; here’s one (it’s also where I got the graphic above): http://www.lenntech.com/water-chemistry-FAQ.htm

HOWEVER, because water dissolves things so well, it is not quite right for our experiments. The water that comes out of the tap is full of other chemicals that would make looking for the pollution very tricky (remember that we are looking for pollution the parts per billion (see the post on June 17). The water that comes out of lakes, rivers or oceans is also full of other stuff too (pollen, dust, algae, etc.)

So, for our experiments, we use several types of water:
1) For our “natural water” samples, we need to filter the floating stuff out of the water. To filter our water, we draw the water through a filter using a vacuum pump connected to a special flask. Any particle bigger than 0.000 7 mm big is filtered out. Pluck a hair from your own head (or a friend’s if you’re feeling pesky). It is about 1 mm wide. The filter will catch things one-thousand times as small.)

These filters were used to filter water from the Arctic Ocean. Andy Warhol meet the Arctic Ocean.

2) For “control” experiments and cleaning, we need really clean water….This water has:
a. Been exposed to intense ultraviolet light to kill any remaining bacteria or other tiny critters
b. Run through “activated charcoal” (like the kind you might buy for an aquarium or a home water filter) to get rid of dissolved organic matter (dead bacteria, for instance)
c. Run through an “ionic exchange packet” to get rid of metals and dissolved non-organic matter.
To further impress that special someone, call this type of water “Barnstead water” or “17 megaohm (MΩ) water” or “milliQ water”.

Even then, there’s still more that can be done (but, for us, this is good enough.).

Interesting Fact to Make You Smarter:
Drinking distilled water is a BAD idea. The chemicals in your body would leave your body and go into the water, leaving you without the chemicals you need!