Water (H 2O) is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart with a hint of blue. It is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances. This allows it to be the "solvent of life". It is the only common substance to exist as a solid, liquid, and gas on Earth's surface.

1. Seawater Chemical Properties

2. Seawater Chemical
Properties
 Saltiness is the most characteristic feature
of seawater.
 Seawater is 96.5% water and 3.5%
dissolved solids.
 Ability of seawater to dissolve large
amount of solids and gases with
chemically reacting with them is its most
important property.
 Majority of solids are present only in
minute concentration.
 But the great volume of ocean makes it
enormous.

3. Seawater Properties
 Dissolved components of seawater can be
divided into
 Conservative (Major) Constituents-found in
concentrations >0.3%
 Non-Conservative constituents- less than
0.3%
 Their concentration may vary in different
geographical locations.
 Do not change their ratios with each other
with changes in salinity.
 They are not removed or added by living
organisms.
 Non-Conservative constituents are
influenced by biological and chemical
processes.

4. ClCl--
The Composition of Seawater
 MAJOR CONSERVATIVE
CONSTITUENTS
11 Major Ions make up 99.9% of
dissolved constituents by weight
>1mg L-1
Concentration
21.9% Anions (Negatively Charged)
12.6% Cations (Positively Charged)
Overall Salinity 34.482% (g kg-1
solvent)
 MINOR CONSTITUENTS
 TRACE CONSTITUENTS
SOSO44
2-2-
BrBr--
MgMg2+2+
CaCa2+2+
KK++
SrSr2+2+ HCOHCO33
--
HH22BOBO33
--
FF--
NaNa++
HH22OO

5. Major and Minor Constituents of
Seawater
Na+
and Cl¯ constitute ions 86% of salt ions present in seawater

6. SEAWATER PROPERTIES-
Major Conservative constituents
Dissolved Ion Chemical
Formula and
Charge
% by weight of
dissolved ions
% by weight of
seawater
Chloride (Cl-) 55.04 1.898
Sodium (Na+) 30.61 1.0556
Sulfate (SO42-) 7.68 0.2649
Magnesium (Mg+) 3.69 0.1272
Calcium (Ca2+) 1.16 0.04
Potassium (K+) 1.1 0.038
Bicarbonate (HCO3-) 0.41 0.014
Bromide (Br-) 0.19 0.0065
Boric Acid (H3BO3) 0.07 0.0026
Strontium (Sr2+) 0.04 0.0013
Fluoride (F-) 0.002 0.0001
Total 99.992 3.4482

7. Chloride
Sodium
Sulfate
Magnesium
Calcium
Potassium
Bicarbonate
Bromide
Strontium
Borate
Fluoride
1.2
4.68
65
140
380
400
1350
2700
10500
19000
1
10
100
1000
10000
100000
The Composition of Seawater
Major Constituents (mg kgMajor Constituents (mg kg-1-1
))

8. Seawater-River Water-Rainwater
 Most abundant salts in river water is least
abundant one in seawater.
 For example carbonate is most abundant in river
water whereas it is least abundant in seawater.
 Rivers previously removed most easily soluble
land salts –Carrying less salts now.

9. Na+K+Mg2+Ca2+Cl-SO42-HCO3-Br-SiO2
0.1
1
10
100
1000
10000
100000
Seawater 10500 350 1340 420 19000 2700 140 65 1.2
River Water 7 2 5 15 9 10 55 0 11
Rainwater 2 0.3 0.2 0.15 4 0.7 0.3 0 0
Na+ K+ Mg2+ Ca2+ Cl- SO42- HCO3- Br- SiO2
A Comparison of Seawater
to other waters
(mg kg-1
)

10. SEAWATER PROPERTIES-
Major Conservative constituents
 This 11 major constituents comprises 99.9% of the total
dissolved material and act conservatively-their concentration
changes only by input or output at ocean boundaries.
 These major constituents are chemically and bio-chemically
inert.

11. Abundant Ions in Seawater
Chloride-Cl¯ 19.0 g/kg
Sodium-Na+
10.6 g/kg
Sulfate (SO4
2-
2.6 g/kg
Magnesium-Mg2+
1.2 g/kg
Calcium-Ca2+
0.4 g/kg
Potassium-K +
0.4 g/kg
Total 35.2 g/kg

12. Seawater Properties
Sources of Salt
 Terrigenous inputs-mainly rivers.
 H2O+CO2>>>>>>H2CO3 (Carbonic
Acid)
 Dissolves rock minerals into ions which
travels down rivers to the ocean
 Acid Rain>>>> pH of around 4.5
Acidic
 Hydrothermal vents
 Dissolving Old sediments-Evaporites
 Steady State-Inputs equals output.

13. Seawater Properties-Salt Sinks
 Salt sinks include the following:
 Evaporation removes only water molecules.
 Remaining water becomes increasingly saline,
eventually producing a salty brine.
 If enough water evaporates, the brine becomes
supersaturate and salt deposits begin to precipitate
forming evaporite minerals.
 Wind-blown spray carries minute droplets of
saltwater inland.
 Adsorption of ions onto clays and some
authigenic minerals.
 Shell formation by organisms.

14. Seawater Properties-Principle of Constancy
of Composition
 Though the actual conc of major constituents vary they are
found in constant ratios-e.g. Ratio of Mg/Cl is same in all the
oceans-Principle of Constant Proportions.
 Regardless of variation in salinity, ratios between the amounts
of major ions in open ocean water are constant.

15. Seawater Properties-Salinity
 Principle of Constant Composition enables
us to determine salinity by measuring the
concentration of only one ion-
 If concentration of one ion is known other
major ions can be calculated from the
known ratios.
 Quantity of chloride ions is usually measured
to calculate salinity by adding AgNO3-Silver
combines with Cl ion.
 Amount of silver reacting with cl in a given
amount of seawater gives us the amount of
chloride present.

16. Seawater Properties-Salinity
 Chloride conc measured in this way is termed as chlorinity.
 Silver also combines with bromine, iodine, florine and chlorine.
 Chlorinity is the quantity of silver required to remove all the
halogens from 0.3285 kg of seawater.
 Chlorinity and salinity are related by the equation-
 Salinity (ppt)= 1.80655 x Chlorinity (ppt)

17. Seawater Properties-Salinity
 A standard seawater sample is required to calibrate the silver
nitrate solution.
 Standard seawater with an adjusted chlorinity of 19.4°/oo is
manufactured and supplied by Institute of Oceanograpahic
Services, Wormly, England.

18. Seawater Properties-Salinity
 Salinity is the total mass, expressed in grams, of all
substances dissolved in one kilogram of sea water
when all carbonate has been converted to oxide,
all bromine and iodine has been replaced by
chlorine and all organic compounds have been
oxidized.

19. Other Salinity Estimation
 Water conducts electricity because of
ions.
 The more the ions the greater the
conductance.
 This relationship enables us to measure
salinity using a conductivity bridge or
salinometer.
 Quick and easy means of analysis-But
the instrument has to be calibrated with
known amount of salinity samples.
 Conductivity bridges are corrected to
temperature.

20. 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.
Why Study Salinity…

21. Significant Values
The average salinity of the world’s
oceans is 35 ppt.
Freshwater has a salinity of <1 ppt.
Inshore waters with salinity values
between 1 - 25 ppt are called
brackish.
Waters with salinity greater than 40
ppt are called hypersaline.

23. Seawater Properties-Salinity Distribution
 Salinity displays a latitudinal relationship
related to precipitation and evaporation.
 Highest ocean salinity is between 20-30o
north and south of the equator.
 Low salinity at the equator and poleward of
30o
results because evaporation decreases
and precipitation increases.
 In some places surface water and deep
water are separated by a halocline, a zone
of rapid change in salinity.
 Water stratification (layering) within the
ocean is more pronounced between 40o
N
and 40o
S.

24. Global Ocean SalinityGlobal Ocean Salinity

25. Residence time is the average
length of time an element remains in
seawater.
The residence time of any element
depends on its chemical activity.
Residence Time
Residence Time =
Amount of element in the ocean
The rate at which the element is
added to or removed from the ocean

26. Residence Time

27. The major source of Calcium (Ca2+
) to
the oceans is river input. What is the
rate at which calcium is added to the
ocean? What is the rate at which
calcium is removed from the ocean?
Calculating Residence Time

28. The major source of Calcium (Ca2+
) to the oceans is river input.
What is the rate at which calcium is added to the ocean? What
is the rate at which calcium is removed from the ocean?
Calculating Residence Time
What we need to know:
Residence Time?
Quantity of Ca2+
in Ocean?

29. Chlorination and Ozonation
 Inorganic Reaction Products of Chlorination
 NaOCl + H2O<-> HOCl + Na+
+ OH-
 HOCl <-> OCl-
+ H+
 hypochlorous acid - hypochlorite
 HOCl + Br -
<-> HOBr + Cl-
 HOBr <-> OBr-
+ H+
 hypobromous acid - hypobromite
 HOCl + OCl-
= Free Chlorine
 HOBr + OBr-
= Active Bromine
 Bromine (as bromide impurity) is sometimes restricted
when selecting salts for seawater formulation to prevent
unwanted reactions

30. Thank you 