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The Chemistry of Water

Water is a phenomenal substance. Its presence brings life and growth to all manner of organisms, and consequently, its absence brings the opposite. Covering 80% of the Earth's surface, it is the only substance that occurs naturally on the planet in all three states; solid, liquid, and gas. For being such an important substance, it is remarkably simple in its makeup. Water is composed of two parts hydrogen and one part oxygen, making the chemical symbol H2O.

Properties of Water

Water exists naturally on the planet in all three states. When the temperature of the water is below freezing (32 degrees Fahrenheit), it is a solid. Between the freezing point and the boiling point, it is a liquid. And above the boiling point (212 degrees Fahrenheit), it is a gas. Aside from the three states, water has a number of unique properties. Most liquids get smaller as they get colder, but not water. Water will stop getting smaller at about 39 degrees Fahrenheit, and then will reverse and start to expand as it gets even colder. Another property is referred to as cohesion, which means that water is attracted to other water.

  • Water Cycle – A good summary, to include a very descriptive picture, on the water cycle on the planet.

Water Molecules

Water is composed of two hydrogen atoms and one oxygen atom. They are attracted to each other due to their electrostatic attraction. All that means is the hydrogen atom is positively charged, while the oxygen atom is negatively charged. Opposites attract, and water is no different. Water is attracted to other water because of this charge attraction. In the same manner that the atoms are combined. The hydrogen of one water molecule will bond to the oxygen atom of another molecule.

  • Sticky Water – An explanation and experiment on the surface tension property of water.
  • Model of a Water Molecule – Explore a three dimensional model of a water molecule, and gain some insight into its construction.
  • Structure Means Foundation – Good information and pictures about the structure and makeup of water molecules.
  • Water Polarity – More information on the charges of the particles that make water and how they attract each other.
  • States of Water – What happens to the molecules as water changes between the three states? Do they remain the same? Find out here.

Solubility

The solubility of a given liquid simply means the amount of a solid that can be dissolved into the liquid. Solubility depends on a few factors such as the liquid being used, the ambient temperature and the atmospheric pressure. At some point, only so much of a solid can be dissolved into the water before it reaches equilibrium, which means that no more of the solid can be dissolved. Think of this as pouring sugar into a cup of coffee. Only a certain amount of sugar can be dissolved into the coffee before no more can be added.

  • Solubility – A chemically-heavy page, here is a lot of information on solubility, to include rules and more on equilibrium.
  • Soluble or Insoluble – A shortlisting on the types of compounds that are or are not soluble in water.
  • Determine Solubility – A chemistry laboratory manual that offers steps on determining the solubility of a substance in water.

Water (Liquid)

When water is in its liquid form, it is the easiest to see. It covers the majority of the planet, after all. Some specific variables have to be just right for water to change states, and those variables have to remain within a certain range for water to remain in whatever state it is in. For example, water must be between 32 and 212 degrees Fahrenheit to remain as a liquid. The primary route for liquid water to return to the Earth's surface is through precipitation. Condensation is the way that water vapor will turn back into liquid water. This causes clouds to form, which in turn causes precipitation, bringing water back to us.

  • Water and Mars – Great information on why water cannot exist on Mars, which illustrates the properties that allow water to exist in certain states.
  • Liquid Water Below Freezing – Water freezes at 32 degrees Fahrenheit, but somehow, scientists have found a way to keep it liquid even below freezing.

Ice

Quite simply, ice is the frozen state of water. As water freezes, it expands and traps air molecules inside of it. Actually, it is the only known substance (non-metallic) that will expand in this manner. This is why ice will float in a glass of water. It does not necessarily need to be in a liquid state in order to become ice. Water vapor can form ice crystals, as in the form of frost. Ice can be found in many forms in the environment, from snow and hail to icebergs and icicles.

  • Physical Properties of Ice – An explanation (with diagrams) on the structure of frozen water.
  • Freezing Water Expansion – Here you can learn more about how and why water expands during freezing.
  • Density of Ice – Molecular reasoning and more diagrams on the density of water and ice.
  • Salt and Ice Water – Questions and explanations on the interaction of salt and water and how it affects the freezing process.
  • Dry Ice – Explore the difference between regular ice and dry ice.

Water Vapor

Water exists as a vapor during its gas state. This can occur through a couple of ways, but mainly at temperatures above 212 degrees Fahrenheit. Above this temperature, water boils and will turn into visible vapor in the form of steam. Water can also exist below this temperature, such as when you are able to see your breath on a cold day. Another form of water turning into vapor is through evaporation, which is the absorption of liquid water into the air. An example of this would be a wet surface allowing to dry. That water didn't disappear, it simply evaporated into the surrounding air.

  • Water Vapor Myths – A brief tutorial, heavy on the text, that debunks some commonly held beliefs.
  • Water Vapor in Space – Water is critical, in all three stages, for human life to exist. Learn more about its existence in space.
  • The Climate – Learn more about the role that water vapor plays in regulating the climate on the planet.
  • Clouds – Some brief information on the formation of clouds from the vapor.
 
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