# 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 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?

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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