Seawater ChemistrySeawater Chemistry

Pure substances that cannot be broken down into simpler chemical entities by

ordinary chemical reactions.

Pure substances that cannot be broken down into simpler chemical entities by

ordinary chemical reactions.

ElementsElements

Periodic Table 112 known elements

Major Elements Comprising the Biological Molecules of Living

Things

Major Elements Comprising the Biological Molecules of Living

Things

• CCarbonarbon• HHydrogenydrogen• OOxygenxygen• NNitrogenitrogen• PPhosphorushosphorus• SSulfurulfur

Other Major Elements of Living Things

Other Major Elements of Living Things

• Calcium (Ca)Calcium (Ca)• Potassium (K)Potassium (K)• Chlorine (Cl)Chlorine (Cl)• Magnesium (Mg)Magnesium (Mg)

Atomic structure

• Atoms are the building blocks of all matter

• Nucleus contains:– Neutrons (no charge)– Protons (+ charge)

• Outer shell(s) contain:– Electrons (– charge)

proton

neutron

electron

hydrogenatom

heliumatom

carbonatom

Electron Shell Configurations of Atoms

1p, 0n, 1e- 2p, 2n, 2e- 6p, 6n, 6e-

atomic number: number of p; #p = #e-

2He2e- and 2p

He

atomic mass (atomic wt.): sum of masses of p+nHe 2p + 2n, atomic mass = 4

4

2He

He

p + n e-

p = n = e- = Atomic number = Atomic mass =

C

Carbon Atom

O16 O17 O18

stable isotopes

IsotopeIsotopeAtoms that differ in the number of neutrons

16

8 O

18

8 O17

8 O#p

#p+n

O

MoleculeTwo or more atoms held

together by chemical bondsOxygenOxygen OO2 2

NitrogenNitrogen NN22

AmmoniaAmmonia NHNH33

Carbon DioxideCarbon Dioxide COCO22

WaterWater HH22OO

MethaneMethane CHCH44

GlucoseGlucose CC66HH1212OO66

IonAn atom that has either gained or lost electrons such that it exhibits a net charge

Na+

Cl-

Sodium (Na) Atom

11 P+

12 No

Sodium (Na+) Ion

11 P+

12 No

Chlorine (Cl) Atom

17 P+

18 No

Chloride (Cl-) Ion

17 P+

18 No

Some Examples of Ions

• Hydrogen H+

• Potassium K+

• Fluoride F-

• Calcium Ca+2

• NitrateNitrate NONO33--

• PhosphatePhosphate POPO44-3-3

Bond TypesBond Types:• Ionic• Covalent• Hydrogen

Ionic BondsTransfer of electron

17 P+

18 No

11 P+

12 No

Covalent Bonding:Covalent Bonding: electron sharing

O

HH

Between Water Molecules

Covalent bond

Hydrogen bond

Boiling Point: 100oCFreezing Point: 0oCDensity: 1g/cm3

Properties of WaterProperties of Water

gas liquid solid

The formation of ice• As water cools to 4°C:

– Molecules slow– Water contracts– Density increases

• Below 4°C:– Hydrogen bonds form– Water expands

• As water freezes:– Expands by 9%

Ice Density vs Temp (oC)

Properties of WaterProperties of Water

1.High heat capacity

2.High heat of vaporization

3.High Surface tension

4.Polarity solvent properties

Properties of SeawaterProperties of SeawaterHeat capacity: • Heat capacity with salinity

Evaporation:• Evaporates more slowly than fw

Specific gravity:• Pure water density = 1.000 g/cm3

• Seawater (2 oC) density = 1.028 g/cm3

Seawater’s Boiling Point:

• As salinity , the boiling point

Seawater’s Freezing Point:

• As salinity , the freezing point

• Salt is an antifreeze- doesn’t freeze until -2oC (@35 o/oo)

Pancake ice

Refractometer Salinometer

• Na+ - Weathering of crustal rock

• Cl- - from the mantle by way of volcanic vents and outgassing from mid-ocean rifts

• Mg ++ - mid ocean rifts

Processes affecting seawater salinity

• Processes that decrease seawater salinity:– Precipitation– Runoff– Icebergs melting– Sea ice melting

• Processes that increase seawater salinity:– Sea ice forming– Evaporation

Salt Ion Ions in sw (0/00)Cl- 18.980Na+ 10.556SO4

2- 2.649Mg2+ 1.272Ca2+ 0.400K+ 0.380HCO3- 0.140Br- 0.065H3BO3 0.026Sr2+ 0.013F- 0.001 Total 34.38

Global surface salinity

Salinity variations

Location/type Salinity

Normal open ocean 33-38‰

Baltic Sea 10‰ (brackish)

Red Sea 42‰ (hypersaline)

Great Salt Lake 280‰

Dead Sea 330‰

Tap water 0.8‰ or less

Premium bottled water 0.3‰

Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.

                                              

                                                                                                          

White sections represent warm surface currents. Purple sections represent deep cold currents

DesalinationDesalinationThe production of drinkable water from seawater

Techniques:1. Distillation- water vapor and condensation2. Freezing- ice crystals form leaving salt behind3. Reverse osmosis- sw is forced through a

semipermeable membrane; only water molecules pass through

4. Electrodialysis- e- charged, semipermeable membranes draw salt ions out of sw

5. Salt absorption- chemically active resins or charcoals are used to draw off the dissolved salt ions fw

Distillation of seawaterDistillation of seawater

seawater

evaporation

freshwater freshwater

Solar energy

Widely used technique

plastic

Reverse Osmosis

Acids

HCL H+ + Cl-

Proton donor, i.e., they donate H+ ions

HCl is a strong acid with a pH 1-2

Na+ + OH- NaOHNH3 + H+ NH4

OH - + H+ H2O

HCO3- +H+ H2CO3

Proton acceptor, i.e., they take up H+ ions

NaOH is a strong base ~pH 12

Bases

Neutralization- HCl + NaOH H2O + NaCl

Buffer- resists dramatic changes in pH; ex. tums, rolaids…buffers stomach acid

Acidic 0-6Neutral 7Basic (alkaline) 8-14

Type of Solution pH Value

0-14

Logarithmic scale

blood

Carbon Dioxide System in the OceanCarbon Dioxide System in the Ocean

Respiration

Photosynthesis

C6H12O6 +6O2 6CO2 + 6H2O

6CO2 + 6H2O C6H12O6 +6O2

Air

Water

CO2 gas

CO2 + H2O ↔ H2CO3 ↔ HCO3- + H + ↔ CO3

2- + 2H+

By-product of respiration

carbonic acidbicarbonate

carbonate

The addition of CO2 makes water acidic

The effects of COThe effects of CO22 in an ocean system in an ocean system

Bicarbonate bufferBicarbonate buffer

Seawater too basic:

H2CO3 HCO3- + H + pH drops

Seawater too acidic:

HCO3- + H + H2CO3 pH rises

Ocean Acidity

Global Ocean Acidity

Consequences of Ocean Acidity

Animals with CaCO3 skeletons affected• Plankton• Corals• Mollusks • Fish

http://news.bbc.co.uk/2/hi/science/nature/7933589.stm

Fisheries

In a high CO2 world, the ocean will be…

• More acidic• More stratified• More oligotrophic, but better

light conditions • Less oxygenated

Consequences of Ocean Acidity

Acid Rain in Marine EnvironmentAcid Rain in Marine Environment

• reduces ability of marine organisms to utilize calcium carbonate

• Coral calcification rate reduced 15-20%

• Skeletal density decreased, branches thinner

Inquiry1. How many neutrons in 7 N?2. Why do all the oceans have relatively the same

proportion of salinity?3. At what temperature is fw most dense?4. Of the following pH’s which is most acidic? 3 7 6 25. Why are there no plants at the compensation

depth?6. Why can a water strider walk on water?7. Besides temperature and salinity, what physical

factor effects thermohaline circulation?8. What is the oceans most dense sea water

called?

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