Water : A Molecule Essential for Life. Thoughts to Ponder…… Why cant we survive more than a week...
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Transcript of Water : A Molecule Essential for Life. Thoughts to Ponder…… Why cant we survive more than a week...
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Water : A Molecule Essential for Life
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Thoughts to Ponder……
• Why can’t we survive more than a week without water?
• How do insects walk on water?• How does water rise up 300 feet from the
roots of a redwood tree?• Why does water take so long to boil?• Why do oil and water not mix?
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Life is dependent on Water
Source: http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-earth.html
Why?
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Water has unique properties that arise from
its structure
http://www.lenntech.com/images/Water%20molecule.jpg
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Water is a Polar Molecule
http://rst.gsfc.nasa.gov/Sect20/water_molecules_con_c_la_784.jpg
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Hydrogen Bond Formation
http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html
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Strength in Numbers!
Source: www.personal.psu.edu/.../ bonddiagram.gif.
Water molecules, with the hydrogen bonds represented by the dotted lines
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Properties of Water due to Hydrogen Bonding
• Cohesion / Surface Tension• Adhesion• High heat capacity• Solvent of polar and ionic
compounds; creates a hydrophobic effect on nonpolar substances
• Density of ice less than liquid water
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•Water molecules
“stick” together
•Creates surface
tension
Cohesion
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• Water molecules are attracted to different molecules
• Capillarity – a special case that results from the relative attraction of the molecules for each other and the solid surface it’s in contact with
Adhesion
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•A great deal of E is
needed to break
hydrogen bonds
•Temperature changes
are minimized
HIGH HEAT CAPACITY
http://i.telegraph.co.uk/multimedia/archive/01549/perspiration_1549996c.jpg
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Specific Heat• Specific heat – amount
of heat needed to change the temperature of 1g. of a substance 1degree Celsius.
• High specific heat allows water to act as a heat sink. Water will retain its temperature after absorbing large amounts of heat, and retain its temperature after losing equally large amounts of heat.
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• Water dissolves polar and ionic substances due to its ability to form hydrogen bonds
Universal SolventThe “Great Dissolver”
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• Water cannot dissolve nonpolar substances.
• Hydrophobic effect- results when water molecules interact with each other and exclude nonpolar substances
• Causes molecules like DNA to fold into their specific shapes
Hydrophobic effect on Nonpolar
substances
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• Ice is less dense then water - it floats
• Ponds, lakes, streams, ocean surfaces freeze from the top down.
• Aquatic organisms receive insulating protection
DENSITY
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• Large amounts of heat E are needed to disrupt hydrogen bonds.• Heat helps water to begin evaporating.•Sweat evaporates using the heat from your body…cools your body down!
Vaporization
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Now that you know the properties of water, what other
ways can you think that it supports life?
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Imagine how life on Earth would change if hydrogen bonding between water
molecules no longer could form