Properties of Water

Properties of Water

properties of water

Water is the most studied material on Earth but it is remarkable to find that the science behind its behavior and function are so poorly understood (or even ignored), not only by people in general, but also by most scientists working with it every day. The small size of its molecule belies the complexity of its actions and its singular capabilities. Many attempts to model water as a simple substance have failed and are still failing. A number of explanations for the complex behavior of water have been published, many quite recently, and many are stirring up quite a controversy. Unlike any other molecule, water’s extremely unique properties, which only a few of them are listed below, make it fit ideally into the requirements for life.

 

Water is so common-place in our everyday lives that people tend to regarded it as just a ‘typical’ liquid. In reality, water is very atypical as a liquid, and it has often been stated that life depends on these anomalous properties of water. In particular, the high cohesion between molecules gives it a high freezing and melting point, such that we and our planet are bathed in liquid water. The large heat capacity, high thermal conductivity and high water content in organisms contribute to thermal regulation and prevent local temperature fluctuations, allowing us to more easily control our body temperature. The high latent heat of evaporation gives resistance to dehydration and considerable evaporative cooling. Also, it is an excellent solvent due to its polarity, high relative permittivity and small size, particularly for polar and ionic compounds and salts. Water is also much smaller than almost all other molecules. For example, it has a smaller volume, and is much lighter than the four other common atmospheric molecules, oxygen (O2), nitrogen (N2), argon (Ar) and carbon dioxide (CO2); with the density of water vapor being just 62% the density of dry air.

properties of water

For those who think of water as just a typical liquid, here are a few observed behaviors that are out of the ordinary to consider:

 

1. Consider clouds. Look up and see the shape and distribution of clouds. Common sense suggests that when water evaporates from the surface of the earth in the form of vapor that it should become evenly distributed in the atmosphere. So, why are there various shapes of accumulated or clustered water molecules in our sky?

properties of water

clouds

properties of water

2. Consider a stream of water bent by static electricity. How and why does that happen?

 

balloon_bending_water

properties of water

3. Consider the water molecule itself: Why is it a liquid at room temperature when the two types of atoms which make up the water molecule (hydrogen and oxygen) are both gases at room temperature?

 

4. Consider the water bridge: how (and more importantly why) does the water climb the sides of the glass container to join with its companion water in the other glass?

 

 

5. Why is water the ONLY substance on earth that expands and becomes less dense when it freezes?

 

6. Why (if water is nothing more than a simple collection of randomly spaced molecules that move freely about within a container), is it the ONLY substance on earth that cannot be compressed?

 

7. Why does water have such a high surface tension that a coin is able to float instead of sinking to the bottom?

 

surface tension

 

After considering these unusual behaviors of water, it should be obvious that water has some very mysterious properties about it.

 

Some of these anomalous properties of water are described in further detail below:

Properties of Water

Boiling Point and Freezing Point

Most people know that water freezes at 0° C and boils at 100° C, however if water were to follow the pattern of the other liquids in its class, it would freeze at -90° C and boil at -60° C, a huge discrepancy. Water belongs to a class of compounds called hydrides in the oxygen family. The melting point and specific heat are calculated according to the molecular weight of each compound. Accordingly, water should be a vapor at normal living temperatures and if water were to follow the pattern determined by other liquids in the same class, there would be very little (if any) liquid water on the planet.

 

Density

Also, water has a very unusual density. Most substances contract (increase in density) as the temperature is reduced. Water is different. The freezing of water molecules causes their mass to occupy a larger volume. When water freezes it expands rapidly adding about 9% by volume. Fresh water has a maximum density at around 4° Celsius. Water is the only substance on this planet where the maximum density of its mass does not occur when it becomes solidified. Water is unusual in that the solid form, ice, is less dense than the liquid form. This is why ice floats and this fact is what allows life to exist in lakes and rivers during the winter months. The water in the seas and oceans has so much salt in them that this lowers the freezing point of the water such that no ice forms in them. The ice found in the seas and oceans are formed of fresh water only.

High Heat Capacity

Water has a high heat capacity, meaning that it changes temperature slowly after gaining or losing energy. In fact, water has the second highest specific heat capacity of any known substance after ammonia. The heat capacity of water is a property directly resulting from hydrogen bonding. The combined effects from hydrogen bonding are enormous, although hydrogen bonds are linked by non-convalent interaction. When heat is absorbed, hydrogen bonds are broken and water molecules can move freely. When the temperature of water decreases, the hydrogen bonds are formed and release a considerable amount of energy. The resistance to sudden temperature changes makes water an excellent habitat, allowing organisms to survive without experiencing wide temperature fluctuation.

High Heat of Vaporization

Heat of vaporization is the quantity of heat required to transform 1 gram of liquid water into its gaseous form. Similarly to the high specific heat of water, the high heat of vaporization is also due the hydrogen bonding. The earth is mostly covered by water, thus water having a higher heat capacity provides a much more stable climate on earth. Evaporative cooling occurs when liquid molecules with the highest kinetic energy escapes as gas, leaving the remaining molecules with lower kinetic energy. This property of water stabilizes temperature in lakes and ponds. It prevents plants and animals from becoming over-heated when exposed to excess heat.

High Cohesion (Surface Tension)

Water-Strider-on-the-SurfaceHigh cohesion is a property in which individual water molecules tend to “stick” with other water molecules due to hydrogen bonding. Hydrogen bonds are very fragile in the liquid form of water, and the property of cohesion is observed when hydrogen bonds, collectively, hold water molecules together. These bonds form, break, and re-form at a high frequency, making water molecules more structured than most other liquids.

properties of water

High cohesion leads to two significant characteristics of water: strong capillary action and high surface tension. Surface tension is also the reason that water droplets form beads rather than spreading out evenly over a surface. What this means is that water molecules have a stronger attraction for each other than for other substances. The arrangement of water molecules result in a strong interface for surface tension, which allows water to act as a stretchable film. This allows things to float on the surface, like the water-strider pictured here. Other than mercury, water has the highest surface tension of any liquid.

properties of water

The cohesion of water molecules is a crucial property in the transportation of water to plants. Strong capillary action is essential to plants in the effective transport of water. Water is willing to diffuse to dry areas especially in a small-spaced fabric, where water will use its cohesion property to attract or pull the water molecules behind before the water molecules evaporate. Therefore, the transportation of water molecules can keep moving even when the plant has a high evaporation rate. Without this property, plants will end up dehydrated and unable to continue photosynthesis.

Amphoteric

Water is known to be amphoteric, which means it is capable of acting as a base or an acid. When the water is a part of a solution, the equilibrium can change. When water reacts with a stronger acid, water will act as a base, and vice versa, water acts as an acid with a stronger base. Due to the oxygen atom’s two lone pairs in the water molecule, water will often act as an electron pair donor, or a Lewis base in reactions involving Lewis acids. However, water can react with Lewis bases, by forming hydrogen bonds between the hydrogen atoms of water and the electron pair donors.

Supercooled Water

Liquid water can be supercooled below 0°C without freezing, but on heating, the supercooled liquid does not expand like other liquids; instead, it contracts to a maximum density at about 4°C; this is very important for the hydrological cycle as it plays a key role in rainwater percolating underground to refill the aquifers.

Memory of Water

The most intriguing quality about water, and one that has only recently begun to be explored, is its ability to “remember.” Water has the ability to hold the frequency or vibration that is acted on it from an outside influence - even after it has been removed. In other words, there is a lasting effect when water is influenced with any form of energy and it has the ability to carry this energy for prolonged periods of time. This property has significant implications for the impacts it can have on our health.

 

To learn about how water retains memory, click here.