How can the unusually low

Because of water's polarity, it is able to dissolve or dissociate many particles. Oxygen has a slightly negative charge, while the two hydrogens have a slightly positive charge. The slightly negative particles of a compound will be attracted to water's hydrogen atoms, while the slightly positive particles will be attracted to water's oxygen molecule; this causes the compound to dissociate.

Besides the explanations above, we can look to some attributes of a water molecule to provide some more reasons of water's uniqueness:. The properties of water make it suitable for organisms to survive in during differing weather conditions.

Ice freezes as it expands, which explains why ice is able to float on liquid water. During the winter when lakes begin to freeze, the surface of the water freezes and then moves down toward deeper water; this explains why people can ice skate on or fall through a frozen lake. If ice was not able to float, the lake would freeze from the bottom up killing all ecosystems living in the lake.

However ice floats, so the fish are able to survive under the surface of the ice during the winter. The surface of ice above a lake also shields lakes from the cold temperature outside and insulates the water beneath it, allowing the lake under the frozen ice to stay liquid and maintain a temperature adequate for the ecosystems living in the lake to survive.

Boiling Point and Freezing Point If you look at the periodic table and locate tellurium atomic number: 52 , you find that the boiling points of hydrides decrease as molecule size decreases. Surface Tension, Heat of Vaporization, and Vapor Pressure Besides mercury, water has the highest surface tension for all liquids.

Viscosity is the property of fluid having high resistance to flow. We normally think of liquids like honey or motor oil being viscous, but when compared to other substances with like structures, water is viscous. Liquids with stronger intermolecular interactions are usually more viscous than liquids with weak intermolecular interactions. Cohesion is intermolecular forces between like molecules; this is why water molecules are able to hold themselves together in a drop. Water molecules are very cohesive because of the molecule's polarity.

This is why you can fill a glass of water just barely above the rim without it spilling. Solid State Ice All substances, including water, become less dense when they are heated and more dense when they are cooled. Liquid State Liquid Water It is very rare to find a compound that lacks carbon to be a liquid at standard temperatures and pressures. This is because of the tiny, weak hydrogen bonds which, in their billions, hold water molecules together for small fractions of a second.

Water molecules are constantly on the move. If they are moving fast enough they become a gas. A gas is a physical state of matter where the molecules are far apart and moving very quickly. But, because of the hydrogen bonds, as water molecules come together they stick to one another for a small, but significant amount of time. This slows them down, and holds them closer to one another. They become a liquid; a different state of matter where the molecules are closer and slower than in a gas. Molecular water, therefore is a liquid at room temperature, a fact that is profoundly significant for all living things on this planet.

Everything dissolves in water. Stone, iron, pots, pans, plates, sugar, salt, and coffee beans all dissolve in water. Things which dissolve are called solutes and the liquid in which they dissolve is called a solvent. The water molecules surround the charged solute; positive hydrogens close to negative charges and negative oxygens close to positive charges on the solute molecule. The polarity of the water molecule makes it an effective solvent and is important in its many roles in living systems.

Have you ever filled up a glass of water to the very top and then slowly added a few more drops? Before it overflows, the water actually forms a dome-like shape above the rim of the glass. This water can stay above the glass because of the property of cohesion.

In cohesion, water molecules are attracted to each other because of hydrogen bonding , keeping the molecules together at the liquid-air gas interface, although there is no more room in the glass.

Cohesion gives rise to surface tension , the capacity of a substance to withstand rupture when placed under tension or stress. When you drop a small scrap of paper onto a droplet of water, the paper floats on top of the water droplet, although the object is denser heavier than the water.

This occurs because of the surface tension that is created by the water molecules. Cohesion and surface tension keep the water molecules intact and the item floating on the top. You will notice that the water appears to be higher on the sides of the straw than in the middle. This is because the water molecules are attracted to the straw and therefore adhere to it.

Cohesive and adhesive forces are important for sustaining life. For example, because of these forces, water can flow up from the roots to the tops of plants to feed the plant. To learn more about water, visit the U. The pH of a solution is a measure of its acidity or alkalinity. You have probably used litmus paper , paper that has been treated with a natural water-soluble dye so it can be used as a pH indicator, to test how much acid or base alkalinity exists in a solution.

You might have even used some to make sure the water in an outdoor swimming pool is properly treated. In both cases, this pH test measures the amount of hydrogen ions that exists in a given solution. High concentrations of hydrogen ions yield a low pH, whereas low levels of hydrogen ions result in a high pH.

The overall concentration of hydrogen ions is inversely related to its pH and can be measured on the pH scale Figure 2. Therefore, the more hydrogen ions present, the lower the pH; conversely, the fewer hydrogen ions, the higher the pH.

The pH scale ranges from 0 to A change of one unit on the pH scale represents a change in the concentration of hydrogen ions by a factor of 10, a change in two units represents a change in the concentration of hydrogen ions by a factor of Thus, small changes in pH represent large changes in the concentrations of hydrogen ions.

Pure water is neutral. It is neither acidic nor basic, and has a pH of 7. Anything below 7. Conversely, bases are those substances that readily donate OH —. Sodium hydroxide and many household cleaners are very alkaline and give up OH — rapidly when placed in water, thereby raising the pH. Most cells in our bodies operate within a very narrow window of the pH scale, typically ranging only from 7.

If the pH of the body is outside of this range, the respiratory system malfunctions, as do other organs in the body.