Properties of seawater

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Properties of seawater
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Where is it on Earth?
Water covers about 71 of Earths surface
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The hydrologic cycle (aka the water cycle)
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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
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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
-
-

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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)
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Effects of Hydrogen Bonds

• Liquid water at room temperature
• Without them water would be a gas
• Cohesion /Adhesion
• Water molecules stick together and to other
  things (adhesion)
• Water droplets on a leaf
• Viscosity
• Tendency to resist flow
• Colder water more viscosity

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More Effects of Hydrogen Bonds

• Surface tension
• Skinlike surface
• Water striders can walk on water
• Ice Floats
• Frozen water is less dense than liquid water

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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)
Cl (Element)
Na (Element)
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Why Study Salinity?

• Determines the distribution of plants and animals
  that live in the ocean.
• Affects other properties of seawater, such as its
  density and the amount of dissolved oxygen it can
  contain.

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Significant Values

• Average salinity of the worlds oceans is 35 ppt
• Fresh water has a salinity of lt 1 ppt
• Inshore waters with salinity values between 1
  25 ppt are called brackish.
• Waters with salinity greater than 40 ppt are
  called hypersaline.

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Salinity Hydrometer Method

• Addition of salts to pure water causes an
  increase in density. Salinity can be calculated
  by measuring the specific gravity of a water
  sample using a hydrometer, correcting for the
  effect of temperature and converting the readings
  to salinity by using conversion tables.
• Specific Gravity density of sample
• density of pure water

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Ionic bonds exchanging
Na atom
Cl atom
Lost.gained
ATTRACTION
Sodium (Na) 11 protons CHARGE 1 10 electrons
Chlorine (Cl) CHARGE -1 17 protons 18
electrons
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Ions atoms with charge
Chlorine -1
Sodium 1
Lost one electron
Gained one electrons
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Salt
Water molecules
Water tends to separate ionic substances
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Salinity

• Salinity Mass of dissolved substances (g)

Mass of water sample (g)
Density of water 1 gram per 1 ml
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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.

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• How much salt is in a 1000 ml sample of 40 ppt
  seawater?
• 40 grams of salt mixed with 960 mL of water

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• How many grams of salt would you find in 4.5
  Liters of a 30 ppt solution?
• 135 g of salt
• How many grams of salt and how many grams of
  water would you find in 2 Liters of 25 ppt
  solution?
• 50 g of salt and 1,950 g of water
• How many grams of salt and how many grams of
  water in 3.2 Liters of 40 ppt solution?
• 128 g of salt and 3,072 g of water

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Seawater

• 11 major constituents that make up 99.99 of all
  dissolved materials

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The Principle of Constant Proportions

• No matter how much the salinity varies, the
  proportions of key elements and compounds do not.

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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

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Determining Salinity

• If you know how much of one sea water chemical,
  you can figure out the salinity using the
  Principle of constant proportions.
• Chlorinity measured in ppt
• The ratio of chlorine, bromine, and iodine ions
  to total salinity
• Salinity 1.80655 x chlorinity

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• What would be the total salinity of a sample
  having 20 ppt chlorinity?
• 36.1 ppt

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Where do the salts come from?

• Weathering of minerals on continents

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Where do the salts come from?
2) Volcanic gases
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OBSERVATION Salts are put into the ocean from
weathering and volcanic gases
PREDICTION SHOULDNT THE OCEANS BE GETTING
SALTIER?
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.but they are not!
SALT INPUT SALT REMOVAL

• Salts are removed by
• Organisms
• Sedimentary rock formation
• Hydrothermal alteration

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Processes affecting salinity

• INCREASE SALINITY
• Evaporation
• Sea ice formation

• DECREASE SALINITY
• Precipitation
• Freshwater runoff
• Sea ice melting

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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

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• 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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