Initial Subject Matter Interest - Water!!

 

Why does ice float? Most things, when cooled, contract and become smaller.  When this happens they become more dense.   Using this sound logic one would expect ice to sink and yet, it floats.  Imagine for a moment the consequences if this were not to occur. All marine life would cease to exist. Ice would accumulate on the bottom of lakes and rivers and oceans killing those species that survive on the floor of these waters including marine life as well as food supplies.  The ice would become greater and greater shrinking the water space until finally the entire space only contained ice.  Instead the ice floats and insulates the water below.  When the temperature increases and the ice melts it becomes slightly more dense and sinks to the bottom of the water and forces warmer water towards the surface circulating oxygen and vital nutrients throughout the water. This is all because the water molecule, famously recited by all as H20, is a bent V-shape molecule instead of the predicted straight line of an oxygen flanked by two hydrogens.

 

I was sitting in the third row aisle seat of my physics class in eleventh grade when I learned this.  Looking back, I didn’t even particularly care for physics at that time, but I was astounded by this revelation. I had looked at water and ice a million times and hadn’t ever realized something so amazing was happening every time an ice cube floated at the top of my glass.  That class was 16 years ago and I remember every bit of it.  It seemed that a little bit of a different world had opened up. I remember wondering what else was out there that I hadn’t thought of. Soon my chemistry classes were explaining further amazing phenomenon about water and I was learning more and more of why water is such an integral part of our survival. I learned that the bent shape and hydrogen bonding occurring in water was responsible for all of this amazing behavior.  This topic came up in my biology, physics and chemistry classes and each had a different lens with which it viewed this wonder.

 

While my favorite topic is still about the floating of ice, there are many other characteristics of water that make it so fascinating and they are all due to its odd structure.  Water has a specific heat capacity over twice as high as something similar like ethanol and over ten times as much as steel.  This means that water can absorb much more heat before its temperature increases. This is vital for not only cooling processes in industry but this is what allows our body to withstand wildly changing temperatures.

 

This is also the reason why the temperature near large bodies of water is so temperate—the water acts as a heat sink and regulates the temperature.  The fact that our Earth is covered two thirds in water is this principle revealed on a gigantic scale—our temperature fluctuations are not nearly as dramatic as those experienced by planets on either side of us without water.  Water also has an incredibly high surface tension. This is what allows a water spider to walk on the water and also allows the phenomenon of capillary action responsible for water climbing through stems in plants. All life requires water with its amazing abilities.

 

My fascination with water has kept me vitally interested in chemistry all these years. It sparked my interest all those years ago and I still look at it with the wonder reserved for those things that never become dull. I have had the good fortune to have an opportunity to teach a few chemistry classes at Freeman High School—the most recent earlier this week. My lesson, fortuitously, was on the subject of intermolecular forces.  These forces explain macroscopic behavior based on microscopic properties of molecules. These include reasons as to why water behaves the way it does.  I walked in, prepared my demonstrations and waited for the students to arrive.  After saying hello and introducing myself, I said, “Things contract when they get cold right?” They obediently shook their heads.  I asked, “And when they do, they get more dense and sink?” They all agreed. Then I looked at them with a smile and said, “So, why does ice float?” I immediately recognized the cocked heads and quizzical looks I received—they were reflections of my own from 16 years ago. Learning about water was not only learning multitude of random facts, it was learning how to think through processes in a logical manner and it was this type of thinking that I hope to teach.