Lecture 1 Water

Lecture 1 Water - Water- 1 Water: some unique properties...

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Water- 1 Water: some unique properties Water: structure Water on Earth The water cycle and natural contaminants Sources of fresh water Uses of fresh water
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Water: some unique properties 1) Most substances become denser and contract when they are cooled, and expand when they are heated. Water is one of the few substances that expands when it freezes. Water is less dense when it is frozen , so its solid form is lighter than its liquid form; in other words, ice floats. This is great if you are a fish: in winter, you can survive in the liquid water under a cover of ice on the surface. Ice will insulate the lower layers of water from the cold air temperatures in winter, and fish and other aquatic organism can survive winter in the temperate zones below the ice. This same property has dangerous consequences for living cells; when living cells freeze, ice crystals are formed, and the expansion ruptures and kills the cells. 1) Water is more dense than most other familiar liquids . As a consequence, liquids less dense than water and insoluble in water float on its surface.
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3) Water has an unusually high heat capacity . Heat capacity is the quantity of heat required to raise the temperature of the substance by 1 °C. This is why water serves as an essential buffer to regulate temperature. Water in the cell is able to absorb large amounts of energy in the form of heat released for example from biochemical reactions. As a result, the water medium acts to maintain a constant cell temperature. 4) Water has an unusually high heat of vaporization . Heat of vaporization is the amount of heat required to evaporate a small amount of water. Large amounts of body heat can be dissipated by the evaporation of small amounts of water (perspiration) from the skin. 5) Water is a very strong solvent , dissolving many types of substances. Substances that will mix well and dissolve in water, e.g. salts, sugars, acids, bases, and some gases: especially oxygen, carbon dioxide (carbonation), are known as "hydrophilic" (water-loving) substances, while those that do not
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This note was uploaded on 04/07/2008 for the course CHEM 100 taught by Professor Caro/kopper during the Spring '08 term at Hendrix.

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Lecture 1 Water - Water- 1 Water: some unique properties...

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