H20: The Wonder Substance—Part 2

By Vicky Harris, Vice President Marketing on November 01, 2016
Vicky Harris
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7 Uncommon Properties Brought to You by Hydrogen Bonds

Water is a familiar alien. Literally and figuratively. For starters, it is not made here. As we explored last week, more and more evidence points to the fact that water did not originate here on Earth. Rather, it came crashing onto our planet by way of comets more than 4.5 billion years ago. The water carried by those comets is indistinguishable from seawater. In 2011, Europe’s Herschel Space Observatory made an interesting discovery about a comet named Hartley 2 when using infrared light to analyze water molecules on its tail. Back then, NASA reported that the comet contained water with the same chemical signature as Earth’s oceans.

Where did the water in that comet come from? Like most comets, this one comes from the distant Kuiper Belt, which contains the primordial material of our solar system and where it is cold enough for liquids to freeze. Water in the comet was formed when hydrogen, the most abundant element in the universe, reacted with oxygen, the third most abundant. Specifically, when the conditions are ripe—such as when dust clumps together and forms solar systems—these two elements easily bond to form H20. Water, in itself, is a very stable substance (more stable than hydrogen or oxygen alone). When water molecules and dust clump together, far from the sun, comets of rock and ice water are formed.

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Alien Properties

Water has some extraordinary properties—indeed, alien-looking properties if you compare it with any other substance here on Earth. These unique traits are the result of hydrogen bonds, which hold H2O together to give water its extraordinary “interstellar-travel-grade stability.”

The distinctive properties exhibited by the hydrogen bonds in H20 include the physical phenomena behind capillarity in plants and animals, its expansion when it freezes, its adhesive properties, and even its role in regulating the temperature of our planet. Today, we explore seven exceptional characteristics of this most amazing substance.

Water is Sticky

The hydrogen bonds between H20 molecules is responsible for two of water’s unique traits, cohesion and adhesion, that make it a “sticky” substance. Cohesion makes water stick to itself quite easily. Cohesion among water molecules is the phenomenon behind capillarity, which transports water against gravity in plants and in also in humans. Adhesion, on the other hand, makes water stick to other things. Both of these forces interact with each other. When water comes into contact with surfaces, the adhesive forces are stronger than the cohesive forces. So, instead of sticking together in a ball (cohesion), water spreads out (adhesion).

A Needle Can ‘Float’ in Water

The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. Hydrogen bonds among surface H20 molecules make them more resistant to stretching or breaking than other liquids. Water has a greater surface tension than most other liquids precisely because of its strong hydrogen bonds. Therefore, water surfaces behave as if covered by an invisible film; we have all have seen this phenomenon when insects glide on the surface of rivers and lakes. In fact, a carefully placed needle (which is denser than water) can float in water because of its high surface tension.

Water Regulates the Climate

Water has a high heat capacity, which is defined as “the amount of heat (usually expressed in calories, kilocalories, or joules) needed to raise a system’s temperature by one degree.” We are alive because of this special property of H2O. Its high heat capacity prevents temperatures from fluctuating outside the range where life can thrive. It is also responsible for mild temperatures in coastal areas and provides for a stable marine environment. Water slows down changes in climate; whether atmospheric temperatures go up or down, water absorbs the heat differential very slowly. A high heat of vaporization is the other property responsible for water’s ability to moderate temperature because it needs a lot of energy to break down the hydrogen bonds. The result: almost 75% of our planet is covered by water. This means that temperature fluctuations are absorbed by water and, thus, take a very long time to affect us.

The Only Substance Commonly Found in All Three Physical States

H20 is the only natural substance found in all three physical states—liquid, solid, and gas—at temperatures normally found on Earth. Because of the high stability caused by hydrogen bonds, water can easily transition between these three states of matter without breaking up. Compare this to the freezing points of the two elements that form it. Hydrogen freezes at -259.16°C and oxygen at -218.79 °C. Likewise, it is quite uncommon to find other substances, which exist naturally as solids, liquids, or gases, transition into another state.

Here’s a Common Occurrence that Should Surprise Us: Ice Floats

We all learned in grade school that solids are denser than liquids. However, if you look at the most common substance on Earth, H20, this is not the case. Water is unusual in that its solid form, ice, is less dense than its liquid form (about 9% less dense). Which is why ice floats. Quora explains this phenomenon quite well from a chemical perspective: “As water cools below 4°C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart. This produces a crystal lattice, which is commonly known as ice.” Another answer provided by this online forum even goes into the “nothingness” of it all: “As the water gets colder and the kinetic energy of the molecules decreases, the hydrogen bonds keep the water molecules apart, forming hexagonal structures with water molecules at each vertex.  In between the water molecules is nothing. Therefore, the solid ice, with its molecules kept at a fairly fixed distance and the crystals holding lots of “nothing” among the water molecules, is less dense than the liquid water.”

Sound Goes a Long Way in Water

The high density of H2O, made possible by its irregular molecular structure, means that sound can travel through it for long distances. Whales, for example, can hear each other over a distance of 1,000 miles. In seawater at 30°C, sound has a velocity of about 3,500 miles-per-hour, depending, of course, upon ocean temperature and pressure. Interestingly, pressure increases with ocean depth, but the temperature of the ocean only decreases up to a certain point, after which it remains stable. The play between pressure and temperature in ocean depths affects how sound waves travel and how far they disseminate. Noise pollution from humans (such as that of ships) has an effect on the speed of sound in water. Scientists at Cornell University undertook a study regarding the effects of noise pollution on blue whales. They concluded, “Twenty to twenty-five million years of evolution [in whale communication] are being undone in a hundred years thanks to increased noise pollution from humans.”

The Universal Solvent

H2O is called the “universal solvent” because it dissolves more substances than any other liquid. This means that wherever water goes, either through the ground or through our bodies, it takes along with it valuable chemicals, minerals, and nutrients. According to a U.S. Geological Survey, “It is water’s chemical composition and physical attributes that make it such an excellent solvent. Water molecules have a polar arrangement of the oxygen and hydrogen atoms—one side (hydrogen) has a positive electrical charge, and the other side (oxygen) has a negative charge. This allows the water molecule to become attracted to many other different types of molecules.” In the case of salt, water disrupts the attractive forces that hold the sodium and chloride in the salt molecule together, dissolving it.

The Life-Giving Alien Substance

The ‘uncommon’ hydrogen bonds that give H2O these exceptional properties and incredible stability as a substance make it possible to have water in such abundance on our planet and elsewhere in our solar system (for more on this, check our first article in this series here). However, as abundant as it is, entire populations go without. For them, fresh water is an alien thing. They do not have it in the quantities necessary to cover basic needs such as drinking, cooking, and sanitation.

We need to change this. Fresh water cannot be alien to a billion people when it is so abundant elsewhere.  In the next article, we will explore the human connection to water and what we can do to make it accessible to all.

 

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