Inorganic Compounds Necessary for Survival

An inorganic compound is a substance that does not contain both carbon and hydrogen. A great many inorganic compounds do contain hydrogen atoms, such as water (H2O) and the hydrochloric acid (HCl) produced by your stomach. In contrast, only a handful of inorganic compounds contain carbon atoms. Carbon dioxide (CO2) is one of the few examples.


Unique Qualities of Water


Water molecules tend to stick together as a result of hydrogen bonding. This creates surface tension which makes water form droplets and allows for organisms like insects to walk on water. Cohesion is also responsible for water's ability to move against gravity from the roots of a tree to its leaves, trees could not survive without this ability. Without trees, there wouldn't be enough oxygen for other life on Earth. 

The animation below illustrates cohesion and surface tension.

Animation 1. View the Cohesion of Water animation on YouTube (opens in new window).

Surface Tension

Cohesion allows for the development of surface tension, the capacity of a substance to withstand being ruptured when placed under tension or stress. This is also why water forms droplets when placed on a dry surface rather than being flattened out by gravity. When a small scrap of paper is placed onto the droplet of water, the paper floats on top of the water droplet even though paper is denser (heavier) than the water. Cohesion and surface tension keep the hydrogen bonds of water molecules intact and support the item floating on the top. It's even possible to float a needle on top of a glass of water if it is placed gently without breaking the surface tension. 

The following video demonstrates surface tension:

Video 2: Click to view the Surface Tension video on YouTube (opens in new window).



Cohesion is also related to water's property of adhesion, or the attraction between water molecules and other molecules. This attraction is sometimes stronger than water's cohesive forces, especially when the water is exposed to charged surfaces such as those found on the inside of thin glass tubes known as capillary tubes. Adhesion is observed when water "climbs" up the tube placed in a glass of water: notice that the water appears to be higher on the sides of the tube than in the middle. This is because the water molecules are attracted to the charged glass walls of the capillary more than they are to each other and, therefore, adhere to it. This type of adhesion is the called capillary action. 

The image below illustrates water adhering to the side of the glass tube forming a meniscus. 

Figure 3. Meniscus of water in a graduated cylinder. The water appears to be higher on the sides than in the middle, since the water molecules are attracted to the glass.The water is measured at the bottom of the meniscus, so it is 21mL.


Universal Solvency

Since water consists of polar molecules, it is able to dissolve many substances into a uniform mixture or solution. The water molecules surround the molecules of the solute, making the water the solvent. Cells and organisms depend on the polarity of water. They are composed of atoms and molecules that dissolve in water to form different aqueous solutions. These solutions are separated into different compartments by layers of nonpolar lipids, which don't dissolve in water. Without this difference, cells could not create specialized areas for different functions, which is one of the most fundamental properties of cells.

Play the animation below that illustrates universal solvency of water.

Animation 2. Click to view the Universal Solvency of Water animation on YouTube (opens in a new window).


Temperature Absorption and Dissipation

Water is an example of a heat sink. A heat sink is a substance or object that absorbs and dissipates heat but does not experience a corresponding increase in temperature. In the body, water absorbs the heat generated by chemical reactions without greatly increasing in temperature. Moreover, when the environmental temperature soars, the water stored in the body helps keep the body cool. This cooling effect happens as warm blood from the body's core flows to the blood vessels just under the skin and is transferred to the environment. At the same time, sweat glands release warm water in sweat. As the water evaporates into the air, it carries away heat, and then the cooler blood from the periphery circulates back to the body core. Temperature is a measure of the average movement of molecules, in water, when we first add heat, there is no rise in temperature because the energy is breaking bonds. Only once, the bonds are broken and the energy start increasing the movement of the water molecules does the temperature rise. Water's unique ability to absorb heat is due to it's relatively high specific heat.



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