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Properties of seawater

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					Properties of seawater
The hydrologic cycle (aka the water cycle)
              Where is it on Earth?
Water covers about 71% of Earth’s surface
           Water
 Molecular
 structure:
  – H2O consists of two
    hydrogen atoms and
    one oxygen atom



Covalent bonds
        electrons are being
shared between the hydrogen
and oxygen atoms
Water: a polar molecule


+
        -      The shared electrons
               (e-) spend more time
               around the oxygen
       -       atom than the
+              hydrogen atoms
               causing the molecule
               to have polarity
                            When charged region
                            comes close to opposite
                            charge, a hydrogen bond is
                            formed




Hydrogen bonds are extremely strong, causing
water molecules to stick together like
magnets (cohesion)
           Salts and Salinity
Salinity includes the total quantity of all
dissolved inorganic solids in seawater.
                                   Sodium chloride is
                                   the most common
                                   and abundant sea
                                   salt
 NaCl (Compound)




Na (Element)        Cl (Element)
        Ionic bonds: exchanging
Na atom                                                  Cl atom

                       Lost….gained




                            ATTRACTION

Sodium (Na)                                     Chlorine (Cl)
11 protons     CHARGE: +1          CHARGE: -1   17 protons
10 electrons                                    18 electrons
  Ions: atoms with charge


   Chlorine
                   Sodium
      -1
                    +1




                  Lost one
Gained one        electron
electrons
                   Salt


                               Water molecules




Water tends to separate ionic substances
                   Salinity
  Salinity = Mass of dissolved substances (g)
              Mass of water sample (g)

Typical seawater = 35 g of dissolved substances
                    1000 g of water

           = 35 0/00   (Per mil = parts per
                       thousand)


          Weight of water = 1 gram per 1 ml
    How much salt to add?
How many grams of salt is in1000 mL of
20 ppt saltwater?

– 1000 ml H20 = 1000 g H20

– Therefore there is 20 grams of salt mixed with
  980 grams of water.
How much salt is in a 1000 ml sample of
40 ppt seawater?

– 40 grams of salt mixed with 960 mL of water
How many grams of salt would you need
to make 4.5 Liters of a 30 ppt solution?

How many grams of salt to make 2 Liters
of 25 ppt solution?

How many grams of salt to make 3.2 Liters
of 40 ppt solution?
The Principle of Constant Proportions
No matter how much the salinity varies, the
proportions of key elements and compounds do
not.
          Determining Salinity
If you know how much of one sea water
chemical, you can figure out the salinity
using the Principle of constant proportions
– Usually the chloride ion (Cl-) is the element that is
  measured which will make up 55.0% of the total
  salinity
– If you measure 19 ppt of chloride per 1000 parts of
  water. What is the salinity?
    19 ppt chlorides = 55.0% of total salinity
    Or, 19 ppt chlorides = .550 x (total salinity)
    Or, 19 ppt chlorides
           .550
   Or 34.5 ppt = total salinity
What would be the total salinity of a
sample having 20 ppt chlorides?

36.4 ppt
     More Salinity Practice
What is the salinity of a water sample
having 15 ppt chlorides?

What about 12 ppt chlorides?

How much salt would you need to make a
solution that has 18 ppt chlorides?
          Where do the salts come from?
   1)   Weathering of
        minerals on
        continents


H20 + CO2              H2CO3
Water and carbon dioxide combine to
form carbonic acid

            CaCO3 + H2CO3                    Ca2+ + 2HCO3-
             Calcite and carbonic acid react to “liberate” calcium
                 Where do the salts come from?
                                       Common volcanic gases

                      others

                        HCl
Percent volume




                       H2S

                       SO2

                       CO2

                 Water vapor

                               0.1            1                10   100




                                     2) Volcanic gases
          OBSERVATION:
Salts are put into the ocean from
weathering and volcanic gases


           PREDICTION:
   SHOULDN’T THE OCEANS BE
      GETTING SALTIER?
            ….but they are not!


    SALT INPUT = SALT REMOVAL

Salts are removed by:
1)Organisms
2)Sedimentary rock formation
3)Hydrothermal alteration
   Processes affecting salinity
INCREASE SALINITY      DECREASE SALINITY
1) Evaporation         1) Precipitation
2) Sea ice formation   2) Freshwater runoff
                       3) Sea ice melting
 Active Transport, Osmoregulators, and
           Osmoconformers
Osmosis through a semipermeable cell
membrane is called
– Passive transport
 The process of cells moving materials
from low to high concentrations is
– Active transport
    Takes energy
Animals that can use active transport to
regulate water concentrations are
osmoregulators
Organisms that have their internal salinity
rise and fall along with the water are
osmoconformers

				
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