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Seawater Chemistry - PowerPoint PPT Presentation


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Seawater Chemistry. Elements. Pure substances that cannot be broken down into simpler chemical entities by ordinary chemical reactions. Periodic Table 112 known elements. Major Elements Comprising the Biological Molecules of Living Things. C arbon H ydrogen O xygen N itrogen P hosphorus

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elements
Elements

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

Periodic Table 112 known elements

major elements comprising the biological molecules of living things
Major Elements Comprising the Biological Molecules of Living Things
  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Phosphorus
  • Sulfur
other major elements of living things
Other Major Elements of Living Things
  • Calcium (Ca)
  • Potassium (K)
  • Chlorine (Cl)
  • Magnesium (Mg)
slide6

Atomic structure

  • Atoms are the building blocks of all matter
  • Nucleus contains:
    • Neutrons (no charge)
    • Protons (+ charge)
  • Outer shell(s) contain:
    • Electrons (– charge)
electron shell configurations of atoms
Electron Shell Configurations of Atoms

proton

neutron

electron

hydrogen

atom

helium

atom

carbon

atom

1p, 0n, 1e-

2p, 2n, 2e-

6p, 6n, 6e-

slide8

atomic number: number ofp;

#p = #e-

2He2e- and 2p

He

slide9

He

atomic mass (atomic wt.):

sum of masses ofp+n

He 2p + 2n, atomic mass = 4

4

2He

p + n

e-

slide10

C

Carbon Atom

p =

n =

e- =

Atomic number =

Atomic mass =

slide11

O

Isotope

Atoms that differ in the number of neutrons

16

8 O

17

8 O

18

8 O

#p+n

#p

O16 O17 O18

stable isotopes

molecule
Molecule

Two or more atoms held together by chemical bonds

Oxygen O2

Nitrogen N2

Ammonia NH3

Carbon Dioxide CO2

Water H2O

Methane CH4

Glucose C6H12O6

slide13
Ion

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

Na+

Cl-

some examples of ions
Some Examples of Ions
  • Hydrogen H+
  • Potassium K+
  • Fluoride F-
  • Calcium Ca+2
  • Nitrate NO3-
  • Phosphate PO4-3
slide19

Bond Types:

  • Ionic
  • Covalent
  • Hydrogen
ionic bonds

11 P+

12 No

Ionic Bonds

Transfer of electron

17 P+

18 No

slide21

O

Covalent Bonding:electron sharing

H

H

slide22

Between Water Molecules

Hydrogen Bonds

Hydrogen

bond

Covalent

bond

slide23

Properties of Water

Boiling Point: 100oC

Freezing Point: 0oC

Density: 1g/cm3

solid

gas

liquid

the formation of ice
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%
slide25

Ice

Density vs Temp (oC)

slide26

Properties of Water

  • High heat capacity
  • High heat of vaporization
  • High Surface tension
  • Polarity solvent properties
slide27

Properties of Seawater

Heat 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
slide28

Seawater’s Freezing Point:

  • As salinity , the freezing point
  • Salt is an antifreeze- doesn’t freeze until -2oC (@35 o/oo)

Pancake ice

slide29

Determining Salinity

Salinometer

Refractometer

slide30

Source of Ocean Salts:

  • Na+ - Weathering of crustal rock
  • Cl- - from the mantle by way of volcanic vents and outgassing from mid-ocean rifts
  • Mg ++ - mid ocean rifts
slide31

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
slide32

Major Solutes in Seawater

Salt Ion Ions in sw (0/00)

Cl- 18.980

Na+ 10.556

SO42- 2.649

Mg2+ 1.272

Ca2+ 0.400

K+ 0.380

HCO3- 0.140

Br- 0.065

H3BO3 0.026

Sr2+ 0.013

F- 0.001

Total 34.38

slide35

Thermohaline Circulation

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

slide36

Thermohaline Circulation

White sections represent warm surface currents.

Purple sections represent deep cold currents

slide37

Desalination

The production of drinkable water from seawater

Techniques:

  • Distillation- water vapor and condensation
  • Freezing- ice crystals form leaving salt behind
  • Reverse osmosis- sw is forced through a semipermeable membrane; only water molecules pass through
  • Electrodialysis- e- charged, semipermeable membranes draw salt ions out of sw
  • Salt absorption- chemically active resins or charcoals are used to draw off the dissolved salt ions  fw
slide38

Solar energy

evaporation

seawater

freshwater

freshwater

Distillation of seawater

plastic

Widely used technique

acids
Acids

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

HCl is a strong acid with a pH 1-2

HCL  H+ + Cl-

bases
Bases

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

NaOH is a strong base ~pH 12

Na+ + OH- NaOH

NH3 + H+ NH4

OH -+ H+ H2O

HCO3- +H+ H2CO3

slide42

Neutralization-

HCl + NaOH H2O + NaCl

slide44

pH Scale

0-14

Type of Solution

pH Value

Acidic 0-6

Neutral 7

Basic (alkaline) 8-14

slide45

pH Scale

Logarithmic scale

blood

slide46

Carbon Dioxide System in the Ocean

CO2 gas

Air

Water

Photosynthesis

6CO2 + 6H2OC6H12O6 +6O2

Respiration

C6H12O6 +6O2 6CO2 + 6H2O

slide47

The effects of CO2 in an ocean system

By-product of respiration

CO2 + H2O ↔ H2CO3↔ HCO3- + H +↔ CO32- + 2H+

carbonic acid

bicarbonate

carbonate

The addition of CO2 makes water acidic

slide48

Bicarbonate buffer

Seawater too basic:

H2CO3 HCO3- + H +pH drops

Seawater too acidic:

HCO3- + H + H2CO3pH rises

slide51

Consequences of Ocean Acidity

Animals with CaCO3 skeletons affected

  • Plankton
  • Corals
  • Mollusks
  • Fish

Fisheries

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

slide52

Consequences of Ocean Acidity

In a high CO2 world, the ocean will be…

  • More acidic
  • More stratified
  • More oligotrophic, but better light conditions
  • Less oxygenated
slide53

Acid Rain in Marine Environment

  • reduces ability of marine organisms to utilize calcium carbonate
  • Coral calcification rate reduced 15-20%
  • Skeletal density decreased, branches thinner
slide54

Inquiry

  • How many neutrons in 7 N?
  • Why do all the oceans have relatively the same proportion of salinity?
  • At what temperature is fw most dense?
  • Of the following pH’s which is most acidic?

3 7 6 2

5. 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?

14