Weird Liquid Named... Water!

Water is the liquid we see everywhere, and thus the one we take to be representative of liquids in general. Which is why we don’t realize how “profoundly odd” water is, how un-representative of liquids it is, writes Philip Ball in H2O. He compares it to using the lives of the residents of Buckingham Palace as representative for British life in general!

“They’re probably the most written-about family in the country – but you could scarcely have chosen a less representative household.”

 

Let’s see the ways in which water is atypical. Most liquids become denser when they freeze. Not water. Ice is famously less dense than water. Which is why ice floats on water, whereas the solid forms of other liquids sink to the bottom of their respective liquids. (This, by the way, has enormous implications for life. Ice is formed at the top of oceans, not bottom. And so when summer comes, the ice at the top melts. If instead, ice had sunk to the bottom, it would never un-freeze and progressively, over the time, the entire ocean would be frozen forever).

 

In addition, water has an unusually high specific heat (the amount of heat it needs to raise its temperature by one degree). This means it takes a lot of heat to increase its temperature, and conversely, it needs to lose a lot of heat to reduce its temperature. That means even a slightly warm ocean current transfers an enormous amount of heat around the world.

 

Water can dissolve almost anything, as we know. That is because of its polarity (electrical charge distribution). And it is chemically reactive to a high degree, which makes it extremely corrosive (think of the rust problem).

 

I didn’t there are many types of ice. No, not in the way of that joke of Eskimos having dozens of names for ice. Rather, there are many different types of ice in the same way graphite and diamonds are different (identical in what they are made of – carbon – yet so different in their molecular arrangement). This is rooted in why the reason why ice floats on water - the molecules of ice are more spread out, so they occupy more space, which makes it less dense:

“The ice crystal contains a lot of empty space.”

In turn, all that empty space means that if you apply a lot of pressure on ice, the molecules can rearrange them into a totally different arrangement. Ice-I just became Ice-II. In fact, there’s so much “empty space” that you can repeat this process of applying more and more pressure to trigger yet more rearrangements, all the way to (hold your breath) Ice-XII (that we know of so far)! Yes, that’s 12 different arrangements of H2O molecules within the category we call “ice”.

 

Balls sums it up well:

“Water is not necessarily unique, or the most extreme example, in displaying any of those anomalies, but their accumulation in a single substance makes it stand out as a decidedly eccentric representative of the liquid state.”