About 70% of the Earth is covered by water. The different properties of water allow it to be labeled as one of the most important substances to life on the planet, and much of it has to do with its chemical structure. For instance, the way the hydrogen and oxygen are bonded allows the molecule to dissolve different substances. In addition, the way in which water freezes allows for aquatic life to survive throughout the winter.
Two properties of water are the melting and boiling point. The melting point of water is 32°F (0°C), and the boiling point is 212° F (100°C) at atmospheric pressure. The addition of pressure will increase the boiling point, and reducing the pressure will cause the boiling point to fall. Therefore, water boils at 156° F (69°C) on Mount Everest and at 256°F (about 124°C) at 15 PSI (107 kPa), the pressure under which many pressure cookers operate. Pressure can also cause the freezing point of water to decrease.
Water is made up of two hydrogen and one oxygen atoms. The arrangement of these atoms is what makes water such a great solvent. Rather than being arranged straight across, the two hydrogen molecules are at a 104.5° angle, making the molecule look like a silhouette of a cartoon mouse. This allows one side of the molecule — the oxygen side — to be negative while the other side — the hydrogen side — is positive. The different charges allow various types of substances to dissolve in water.
Since water has this unique makeup, it is called a universal solvent. Different substances from sugar, to salt, to acids such as vinegar are able to be dissolved in water. This is good news for people who are trying to get water-soluble minerals into their diets but bad news for anyone trying to dissolve oil in water. Ironically, the same property that makes it possible for water to be a universal solvent is what causes this phenomenon. Oils and fats do not have a charge, and the water molecule is more attracted to itself than the fat and so will pool to one area.
Another of the interesting properties of water is its high specific heat. Specific heat is the measurement of how much heat it takes to raise the temperature of 1 gram of water 1°C. Water can absorb a lot of heat without changing temperature, and so it has a high specific heat. This results in water cooling down and heating up much more slowly than the air around it.
Ice also exhibits an interesting property. When most things freeze, they become dense and will sink to the bottom of their liquid versions. Water does become denser as it cools, but as it approaches freezing, it starts to become less dense and floats. This phenomenon helps aquatic life survive in larger lakes throughout the winter. The surface of the water will freeze, leaving the water below unfrozen.