Properties of Water - The properties of Water Lecture 4A...

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The properties of Water Lecture 4A Freshwater Ecosystems EVPP/BIOL 350 Dr. Kim de Mutsert
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Water The abundance of water is one of the most unique aspects of Planet Earth – “The Blue Planet”
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Properties of Water 1. Molecular Structure 2. Liquid Nature of Water 3. Specific Heat 4. Density vs. Temperature 5. Solvent Properties 6. Viscosity 7. Surface Tension
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Molecular Structure
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Molecular Structure Water is H2O, two atoms of hydrogen attached to one atom of oxygen Because the O atom has a greater mass the electrons spend more time near it than near the H atoms Thus, a charge asymmetry is created such that the O end of the molecule has a negative charge and the H end has a positive charge, this a called a dipole .
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Hydrogen Bonds This charge asymmetry results in weak bonding of adjacent molecules The net result is that water has some unusual properties It is a liquid at “room” temperature when it should be a gas The bonds between adjacent water molecules are called hydrogen bonds
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Liquid Nature of Water Melting points (°C) of related hydrides: H4C -182 H3N -78 H20 0 HF -83 H2O 0 H2S -83 H2Se -64 H2Te -48 Boiling points (°C) of related hydrides: H4C -161 H3N -33 H20 100 HF 19 H2O 100 H2S -60 H2Se -42 H2Te -2 If water behaved as other related hydrides, it would melt at about -50°C and boil at about 0°C, making life as we know it on Planet Earth impossible
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Liquid Nature of Water The explanation for water’s above- predicted boiling point lies in its ability to form quasi-polymers These hold the molecules closer to one another as is required of a liquid It takes more energy (higher temperature) to break these bonds and convert water to a vapor
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Solvent Properties Water is considered the “universal solvent” because of its abilities to dissolve a wide range of chemicals This ability is related to its dipolar nature The polar parts of the water molecule can bind to negative and positive ions like chloride (Cl-) and sodium (Na+)
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Heat One calorie is defined as the amount of heat required to raise the temperature of 1 g of water by 1°C High Heat Capacity: Additional energy required to melt or evaporate 1 g of water 80 calories of energy (heat) required to melt ice (while temperature remains constant) 540 calories of energy (heat) required to evaporate water (while temperature
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Density by Temperature Density is defined as the weight or mass of a substance per unit volume (g/cm3) The density of water varies in an interesting way with temperature The first thing to notice is
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This note was uploaded on 01/23/2012 for the course BIOL/EVPP 350 taught by Professor Kimdemutsert during the Fall '11 term at George Mason.

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Properties of Water - The properties of Water Lecture 4A...

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