HYDROLOGY

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					HYDROLOGY
              Hydrosphere

 ~71% of Earth’s surface is covered in
  water
 What sets Earth apart from other planets
 Not always here
 4.5 BYA Volcanic Eruptions
   – Lava – hot
   – Gas – water vapor
   – Ash – blocks sun
      • Cools temperature
 Water vapor condenses
 Rain falls
 Oceans form
          Water Conservation

 Most of the water on Earth is not suitable
  for human use
 97% is saltwater
 80% of all freshwater is frozen in polar
  ice caps
 the majority of remaining freshwater is
  polluted or otherwise unsuitable for use
 1/3 of Earth’s population does not have
  access to suitable water
   – Landforms
   – Vegetation
   – Distance to a body of water
   – Drought
   – Contamination
   – Pollution
 The one drop from our experiment is not
  available to people all the time.
             Properties of Water
Most important compound on Earth
Tasteless
Odorless
2 Hydrogen atoms to 1 Oxygen atom
Polarity
Universal Solvent
Cohesion
Adhesion
Specific Heat
Density
                   Polarity

 The hydrogen and oxygen atoms are
  connected by polar covalent bonds
   – unequal sharing of electrons
 Since the oxygen is bigger than
  hydrogen, the electrons tend to stay
  closer to the oxygen
   – Oxygen has a slightly negative charge
   – Hydrogen end has a slightly positive charge
           Water Molecule




Polarity creates poles in water molecules like
a magnet.
 Water has a variety of unusual properties
  because of attraction between these polar
  molecules.
   – The slightly negative regions of one molecule
     are attracted to the slightly positive regions
     of nearby molecules, forming a hydrogen
     bond.
   – Each water molecule can form hydrogen
     bonds with up to 4 neighbors.
                  Hydrogen Bonds

   Hold water molecules              Extraordinary Properties that
    together                           are a result of hydrogen
   Each water molecule can form       bonds:
    a maximum of 4 hydrogen             –   Cohesive behavior
    bonds                               –   Resists changes in temperature
                                        –   High heat of vaporization
   The hydrogen bonds joining
                                        –   Expands when it freezes
    water molecules are weak,
                                        –   Versatile solvent
    about 1/20th as strong as
    covalent bonds.
   They form, break, and reform
    with great frequency
 Polar = uneven distribution of electrons
   – Has a charge
 Nonpolar = even distribution of electrons
   – No charge
 Like dissolves like
   – Polar dissolves polar
   – Nonpolar dissolves nonpolar
             Universal Solvent
 Water is an universal solvent
   – Most substances will dissolve in water
 Ex. Salt dissolves in water
 Solvent: substance in which other
  substances dissolve
   – water
 Solute: substance that dissolves
   – salt
Why does salt dissolve in water?




Positively charged sodium ions attract the
negative oxygen side of water.
Negatively charged chloride ions attract the
positive hydrogen side of water
           Water as a Solvent

 Substances dissolved in fresh and salt
  water that are important
   – Dissolved gases: oxygen and carbon dioxide
   – Dissolved salts and minerals/nutrients
     (not nitrates)
                  Adhesion

 Adhesion: molecules that are not alike are
  attracted
   – Ex. Water to walls of a test tube or plant
     walls
   – Think sticky
   – Water to the side of a graduated cylinder
      • Meniscus
                Cohesion

 Cohesion: molecules of the same kind
  stick to one another.
  – Ex. The reason drops form
Organisms Depend on Cohesion

   Cohesion is responsible for
    the transport of the water
    column in plants
   Cohesion among water
    molecules plays a key roll in
    the transport of water against
    gravity on plants
     – Capillary Action
   Adhesion also contributes to
    capillary action as water
    adheres to the wall of the
    vessel.
                                     Ex. Water in a straw
               Surface Tension
 A measure of the force necessary to stretch or break
   the surface of a liquid, is related to cohesion
    – Water has a greater surface tension than most other
      liquids because hydrogen bonds among surface
      water molecules resist stretching or breaking the
      surface.
    – Water behaves as if covered by an invisible film.
    – Some animals can stand, walk, or run on water
      without breaking the surface.
    – Is why we can “skip” rocks on water
                      Water Strider
Can walk on water without breaking the surface tension of water.
Specific Heat

 Specific Heat is the measure of the heat that
  must be absorbed or lost for one gram of a
                                            o
  substance to change its temperature by 1 C.
   – A lot of heat energy required to break
     hydrogen bonds, water resists temperature
     change
      • Most heat goes to breaking the bonds..not
        much left to raise temperature
 Water = high specific heat
   – This is why it doesn’t usually snow in
     Wilmington:
   – The ocean doesn’t change temperature very
     rapidly
 Has a moderating effect on our weather
                       Density
 Density: how packed together a material is
    – Mass/volume
    – Units: g/mL
 More dense it sinks
 Less dense it floats
Problem: If 60 mL of a liquid has a mass of 30g. What is
   the density of the liquid?
                        D=30g/60mL
                         D=0.5 g/mL
            Density of Water

 Water is one of the only substances that
  is less dense as a solid than as a liquid.
 Prevents water from freezing from the
  bottom up.
Buoyancy

     The force of
      buoyancy is equal to
      the weight of the
      fluid displaced
     An object with
      greater volume will
      be pushed up with
      more force.

				
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