Water and Seawater

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					Water and Seawater
I. The Water Molecule
   A. General
      1. molecule – a group of 2 or more atoms held together by
         mutually shared electrons.
   B. Geometry
      1. Covalent bonds – sharing of electrons, relatively strong,
         needs a lot of energy to break bonds.

          a. Both H+ atoms on the same side – bend gives water
              its unique properties.
   C. Polarity – slight overall negative charge to O- side and
      slight overall positive charge to H+ side – like a bar magnet
D. Interconnection of molecules
   1. hydrogen bonds – weak , form between H+ of one
       molecule and O- of another molecule.
     a. Cohesion – molecules “cling” to one
     b. Surface tension – cohesion
        gives water’s surface a thin “skin”.
       Results from H+ bonds on
       outermost layer.
    Penny and Wax Paper Activity
    c. Capillary action – Water rises up in thin tubes
          ex. Water to top of trees.

E. Universal solvent – water molecules reduce the attraction
   between ions with opposite charges. Dissolves nearly
     a. electrostatic attraction – attraction between oppositely
        charged ions = ionic bonds
        *in water electrostatic
         attraction is reduced
         Na+ ions are attracted
         to the O- side. Cl- ions
         are attracted to the H+ side
II. Waters Thermal Properties
   A. Changes of State
       1. Solid, Liquid and gas
       2. The attractive forces between the molecules must be
          a. Hydrogen bonds
   B. Energy needed to change state
       1. Heat – energy of moving particles
          a. Kinetic – moving
          b. Calorie – amount of heat required to raise the
             temperature of 1 gram of water by 10C
      2. Temperature – direct measurement of the average
         kinetic energy of the molecules that make up a
            temperature = KE        in temp = +heat or -heat
C. States
   1. Solid – molecules have rigid structure, does not flow
   2. Liquid – molecules flows past each other
   3. Gas – molecules no longer interact except during
      random collisions. Flows very freely.
D. Freezing and Boiling points
   1. Melting Point – energy added. Temperature at which
      melting (solid to liquid) occurs
   2. Freezing Point – energy removed. Temperature at
      which a liquid becomes a solid. 00C or 320F
    3. Boiling Point – energy added. Temperature at which a
        liquid becomes a gas 1000C or 2120F
    4. Condensation Point – energy removed. Temperature at
        which a gas becomes a liquid 1000C or 2120F
*this is all due to the geometry and polarity of the water
  molecule. If water was like all other molecules, life would not
  exist on Earth.
E. Heat capacity – the amount of heat required to raise the
   temperature of 1 gram of any substance by 10C
       HC – can absorb or loose large amounts of heat with
       only small changes in temperature. ex H2O
       HC – substance that changes temperature rapidly ex.
   1. Can affect weather
       – sea and land
       Water and Land
III. Density – (d=m/v)
   A. Affected by:
       1. Temperature
          a. Most substances – decrease temperature =
             increased density ex. Warm air rises, cold air sinks
             decrease temperature – molecules lose energy and
             slow down, occupy less space – shrinkages =
             thermal contraction.
          b. Water
             1.) Thermal contraction occurs to 4OC (39OF)
                 density increases. 4OC – 0OC density decreases
                 (expands) ice is less dense than water so it floats
                 a.) volume increases
            Density Lab
       2. Pressure
          a. Increase pressure = increase in the number of water
             molecules in a given space – inhibits the number of
             ice crystals that can form.
       3. Salinity – dissolved substances
          a. Increase salinity – inhibits the formation of H+ bonds
              – reduces the # of ice crystals that can form
               ex. Salt water rarely freezes
                    Salt roads in winter.
                Why does the bay freeze?
IV. Seawater
   A. Salinity – total amount of solid material dissolved in water.
       Includes dissolved gasses. Ratio of mass of dissolved
       substances to the mass of water.
       1. Typically ~3.5 % or 35 0/00 96.5% fresh (pure water)
2. Variations
   a. Brackish – 10 0/00 (1%) Salinity. Areas where fresh
      water and sea water mix.
       Where is this?
   b. Hypersaline – 42 0/00 (4.2%) – high rate of
      evaporation, limited open ocean circulation ex. Red
      Sea, Dead Sea (330 0/00), Great Salt Lake
      (280 0/00)
           How to avoid goiters WS
 3. Components
    a. 99% - Cl, Na, S, Mg, Ca, and K
    b. Others – see table 6-2 pg. 175
4. Measurement
   a. Early – evaporating and carefully weighing
       precipitated salts. Time consuming
       b. Salinometer – measures seawaters electrical
          conductivity which increases as more dissolved
          substances are dissolved in water.
       c. Principle of Constant proportions – Challenger
          expedition – major dissolved components in sea
          water occur nearly everywhere in the exact
   5. Dissolved components added and removed
       a. Added – river run-off. Erosion of rocks
       b. Removed
          1.) sea salt spray (3.3 billion metric tons)
          2.) Infiltration of sea water along mid-ocean ridge
               near hydrothermal vents.
          3.) Deposited as sediment within shells
          4.) Salt deposits when seas dry up
B. Dissolved gasses in sea water
   1. General
      a. Important for marine organisms WHY?
  b. Amount of dissolved gasses depends on
     1.) pressure
      2.) temperature
      3.) ability to escape to atmosphere.
   c. Gas exchange between atmosphere and ocean
      1.) at surface, small amount of AG dissolves into
      2.) wave action enhances air-water contact – wind
      3.) O2 and CO2 are altered by biological and
          chemical processes
2. Oxygen
   a. Increases at surface due to photosynthesis by marine
      algae and exchange with atmosphere.
   b. Decreases rapidly with depth Why?
       1.) algae only in sunlit layer
       2.) used by animals living deeper
       3.) deep water is higher than intermediate depths. Due
           to origination at surface of polar regions (low
           temperature = increased O2) down-dwelling
              Measuring O2
        Scientists to monitor oceans oxygen levels article
   3. Carbon dioxide – one of the most abundant gasses in
      sea water due to its high solubility.
      a. Used for photosynthesis
      b. Also affected by volcanic activity
          Measuring CO2
C. Acidity/Alkalinity
   1. General
  a. Acid – compound that releases Hydrogen (H+)
      ions when dissolved in water.
   b. Alkaline (base) – releases OH- (hydroxide) ions
      when dissolved in water
2. pH scale

   Ocean water is slightly acidic CO2 – Carbonic acid
    a. Carbonate buffering system
       1.) shells (CaCO3) act like an antacid –
           neutralizes acidity
         2.) large buffering capacity for CO2 – important
              implications for climate change. Oceans remove
              large amounts of CO2 (Greenhouse Gas) without
              a significant change in seawater pH
               pH testing
D. Processes Affecting sea water salinity – change in either
   the amount of dissolved substances or the amount of
   1. Decreases salinity
       a. Precipitation, runoff, melting, icebergs, melting sea
          ice – add more fresh water.
   2. Increases salinity
      a. Formation of sea ice and evaporation
3. The Hydrological Cycle
E. Surface and Depth Salinity Variation
  1. Surface Salinity Variation
      a. lowest at high latitudes – Why
      b. highest at mid latitudes – atmospheric circulation of
         warm dry air – increased evaporation, decreased
         precipitation and run-off (deserts)
      c. equator – increased evaporation, increased
         precipitation and run-off
2. Depth Salinity Variation
   a. Low latitudes
      1.) surface – high salinity
      2.) depth – intermediate
   b. High latitudes
      1.) surface – low salinity
      2.) depth – intermediate
 *all processes that affect salinity occur at the surface.
  Have no affect on deep water
3. Halocline – layer of rapidly changing salinity with depth.
  Separates layers of differing salinities
F. Sea Water Density
   1. General
      a. Pure water 1.00 g/cm3 at 40C (390F)
      b. Seawater averages between 1.022 g/cm3 and 1.030
         g/cm3 (depending on salinity)
      c. sea water continues to increase in density until it
         freezes at -1.90C (28.60F) then it behaves like fresh
         water (decreases density)
     d. Density of sea water caused water masses to sink or
          ex. Add sea water (d=10.30 g/cm3) to fresh water.
          Sea water would sink – deep ocean currents
     e. Temperature, salinity and pressure influence seawater
          1.) as temperature increases, density decreases –
surface      thermal expansion
          2.) as salinity increases, density increases – increase in
              dissolved material.
deep      3.) as pressure increases, density increases
          compressive effects
    2. Pycnocline – a layer of rapidly
       changing density
    3. Thermocline – a layer of rapidly
              decreasing temperature