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Physical and Chemical Properties of Water.pptx

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					Physical and Chemical
 Properties of Water
The Water Molecule
         —   Water is a compound
             —   Compound: substance that contains
                 two or more different elements.
             —   H2O: 2 hydrogens and 1 oxygen

         —   A water molecule is held together by
             a Covalent Bond.
             —   Molecules are held together by
                 shared electrons.

         —   2 or more water molecules are held
             together by Hydrogen bonds
             —   Hydrogen Bond-When a hydrogen
                 atom is linked to another atom by
                 electrostatic forces. Much stronger
                 than covalent bonds.
             —   Gives water properties such as
                 cohesion and adhesion.
A Polar Molecule
        — Molecule behaves like a magnet.
        — Its positive end attracts
          negatively charged particles
        — Its negative end attracts
          positively charged particles
        — Most salts are held together by
          opposite charges (Na+, Cl- is
          NaCl) and when these come in
          contact with water, they are
          pulled apart.
           —   This is why water is a good
               Solvent (dissolve things well).
       Properties of Hydrogen
              Bonding
— Cohesion-Allows individual water molecules to stick to
  each other (cluster), giving water a high surface tension.
  It also allows for diffusion. (think of the water on the
  penny or paper clip on water…this is due to cohesion
  and surface tension).

— Adhesion-The tendancy of water to stick to other
  materials (making them wet). (capillary action in soil or
  water running up a paper towel).
 Physical Properties of Ocean
            Water
— Heat Capacity

— Temperature

— Density

— Salinity

— Ability to transmit light

— Ability to transmit sound
               Heat Capacity
— Heat: A measure of energy produced by vibration of
  atoms or molecules.
— Temperature: A measure of how rapidly molecules are
  vibrating.
— Heat Capacity: The amount of heat it takes to raise 1
  gram of a substance by 1 degree Celsius.
— Water has highest heat capacity of any substance.
  — From hydrogen bonding!
  — Means water’s temperature does not rise or lower very
    easily.
Measuring Heat
       — Calories per gram

       — Heat=Specific Heat x
         Change in Temperature

       — How would we calculate
         Specific Heat?
Temperature and Density
            — Water becomes more dense
              as it gets colder.
            — UNTIL: It reaches 4 degrees
              Celsius.

            — Then water becomes less
              dense as it freezes

            — Why does this happen?
              Hint: Density=Mass/Volume
Salinity and Density
           — Note that a higher salinity
             gives water a higher density.
           — Note also that salinity
             decreases the temperature
             at which water freezes
              — So ocean water freezes at
                about -2 degrees Celsius
              — Fresh water freezes at 0
                degrees Celsius
      Temperature, Salinity, Density

                                            10 C
                                            12 PPT
                                            1.010 g/cm3

                                            21 C
                                            15 PPT
                                            1.010 g/cm3




Note that two samples of water can have
the same density at different combinations of
temperature and salinity.
           Density Summary
— Density of Seawater is 1.020-1.030 g/cm3
— Fresh is only 1.000 g/cm3
— Cold, salty water is more dense than warm, less salty
  water.
— Seawater’s density increases with increasing salinity,
  increasing pressure, and decreasing temperature (until
  right before it freezes).
— Two samples of water can have the same density at
  different combinations of temperature and salinity.
Light in the Ocean
                -Long wavelengths
                are absorbed at
                shallow depths.

                -Blue light
                penetrates to
                the deepest
                levels and is
                reflected back

                -To our eyes.
                this is why the
                oceans appear
                blue.
                  Photic Zone
— Photic Zone: The depth light penetrates in the ocean.
  — 200 meters in clear, tropical waters
  — 100 meters in most ocean waters
  — All photosynthetic organisms live in this zone (corals, sea
    grasses, algae, phytoplankton).
  — Infrared radiation is converted to heat
  — Most of life in the ocean is found here.
                Aphotic Zone
— Aphotic Zone: Zone below photic zone that is in
  complete darkness.
  — About 1% of light penetrates to a depth of 100-125
    meters
  — Absolutely no light penetrates below 1,000 meters.
  — ¾ or 75% of the ocean is in total darkness!
                              Refraction
    — Refraction: Bending of waves. Light acts as a wave
      and a particle.



Light bends toward
The normal
When it travels
From a lower
Density to higher
Density.

Light bends away from
The normal when it
Travels from higher density
To lower density.
              Snell’s Law




Nair=1
Nwater=0.75
         Sound in the Ocean
— Sound: Form of energy transmitted through a medium
  through vibration of molecules.

— Sound intensity decreases through seawater due to
  spreading, scattering, and absorption.
  — Sound travels about 1,500 m/s in seawater
  — Sound travels 334 m/s in air at 20 degrees C.
    — Speed of sound increases as temperature, pressure, and
      salinity increase.
    — Low frequencies travel farther than high frequency
                 Sofar Layer
— The minimum velocity layer

— 1200 m depth in North Atlantic down to 600 m depth in
  North Pacific

— Sound waves move at minimum speed and allow for
  sounds to heard for great distances since refraction
  keeps sounds waves within the layer.
                   Shadow Zones



80 M




 Maximum sound velocity occurs at 80 m which deflects sound and causes
 a shadow zone.
                  SONAR
— SONAR: Sound Navigation and Ranging.

				
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posted:2/11/2014
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Lingjuan Ma Lingjuan Ma
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