Oceans are unique to Earth in our Solar System.
70% of earth surface is water as Oceans.

Oceans are important and influence:

• Climate
• Distribution of Solar Energy Through Ocean Currents
• Waste Toxins by Dilution
• Major player in Hydrologic Cycle
• Carbon Dioxide Cycle as Reservoir
  (as dissolved CO2, H2CO2, CaCO3)

Two Major Zones:

1. Coastal Zone

2. Open Sea

Coastal Zone -

Nutrients Travel From:

Land
Rivers
Coastal Zone of the Ocean

Open Sea

Euphotic Zone - Sun light Penetration - Photosynthesis
Bathyal Zone - almost no light
Abyssal Zone - no light

Complex Coastal Zone Configurations

Chemical Composition of Sea water

Resources from Sea water

• Drinkable and industrial water after Desalination

• Current Sea water extracts of commercial value:
  NaCl
  Mg
  Br2

• Deep ocean deposits of Mn, Cu, and Zn

• Oil and Gas from Offshore drilling

pH of Sea Water - 7.8 to 8.3

Note:
Almost all waste in rivers and air eventually is deposited in the oceans.
An old saying goes - "The Solution to Pollution is Dilution"

Chemical Components in Ocean and Fresh Water

CO2 in atmosphere will dissolve equal to the partial pressure

CO2 will react with H2O

pH of a solution open to atmospheric pH and in equilibrium with calcite (CaCO3) is 8.4.

The pH of ground water in contact with calcite, but not with CO2 is 9.9.

Calcite (CaCO3) is the major constituent of sea shells, chalk, marble, limestone.

A complex combination of equilibrium combine to set the pH.

pH

Many topics are related to pH and its interaction with other components

Natural Precipitation pH = 5.6

Sea Water pH = 7.8 to 8.3

Soil can have K+, Ca2+, Mg2+ and NH4+ replaced by H+ depending on Equilibrium.

This is primarily due to the following Equilibrium;

Why ?

What is pH ?

Definition of Acids and Bases

The Bronsted and Lowery definition (1923) -

Recall the p-functions

pH applied to acid

Given: pH = 5.1

Remember Hydronium ion

There are no isolated H+ (proton) in aqueous solution.
Rather:

However, the concentration of liquid H2O is relatively constant compared to the ions and it is a liquid and liquids and solids do not appear in equilibrium constants (a constant 55 mole)(and their activity is = to 1).

Review strong and weak acid- base ionizations and buffer behavior.

Conjugate acid - is an ion remaining after accepting a proton

Acid and bases

Conjugate base is the entity that remains following the donation of a proton and a conjugate acid is what results after accepting a proton.
(c- = conjugate)

Strong acid or bases dissociate in water completely and leave no undissociated molecules.

Weak acid or bases do not dissociate completely and leave varying amounts of both species in solution.
Strong acids and bases react completely:

Water is an Amphiprotic solvent acting as either a proton donor or acceptor.

Chemical Equilibrium:

Equilibrium Constant - K (Keq)

Keq is a temperature dependent constant.

At dilute concentrations -
ion activity (a) is approximately = to ion concentration

Direction of the reaction and the equilibrium constant -

Important and common types of equilibrium constants.

• Dissociation : Ion-Product constant
  Example for Water
  

• Dissociation of a weak acid or base
  Example for Ka or Kb
  

• Molecule and ion in saturated solution precipitate as solid material
  Example for Ksp - solubility product constant
  

Total Alkalinity

Buffers

Two competing reactions occur simultaneously

Depending on the strength of these equilibrium the solution will be acidic or basic

If the first equilibrium lies far to the right and is dominant, then the solution will be acidic.

If the second is dominant, then the solution is basic.

Ion Exchange

Both Cation (+ ions) and Anion (- ions) occur.

This process goes on primarily in clay an organic soils particles, but occurs to some extent on all geological surfaces.

General order of cation exchangeability for common ions in ground water is:

Divalent ions are more strongly bonded and tend to replace monovalent ions.

Note:
Where does NH4+ fall in this relationship?
What is the significance of this?

Ion exchange is a reversible reaction.

Why is this important?

Na+ can replace Ca+2 in the soil if the water used to irrigate the land is salty (contains high concentrations of Na+ ions). This destroys the soil structure by dispersing the clay particles.

Selectivity (Preference) in ion exchange can be 10^(1) to 10^(4) for one ion over another.

Complexation

Metal Ions react with electron-pair donors to form:

1. Complex Ions	example Cu(NH3)42+
2. Coordination Compounds	example Cu(NH2CH2COO)2

The compound is formed by the donation of a pair of electrons by the ligand
(ligand - a proton donor in complex formation)

The number of bonds formed per molecule is referred to a "Dentate" meaning tooth-like.

Unidentate reagents form a single bond per molecule.

Examples of Unidentate Ligands

Chelating compounds

The most important group of complexing organic molecules are the Aminopolycarboxylic Acids

These carboxylic acids are frequently found in humic acids and organic mater in soil.

These are large organic compounds that possess amines and carboxylic acid groups.

They tend to form 1:1 complexes with metal ions and are usually 4 or 6 (tetra- or hexa- dentates).

An example of an aminopoycarboxylic acid:

EDTA stands or Ethylenediaminetetraacetic acid.

It is a Hexadentate ligand with six potential bonding sites two amino groups and four carboxyl groups.

EDTA is water soluble and has four ionizable groups

It is a zwitterion of the form H4Y

The ionization of EDTA is pH dependent

The dissociation constants are:

K1 = 1.02 x 10^(-2)
K2 = 2.14 x 10^(-3)
K3 = 6.92 x 10^(-7)
K4 = 5.50 x 10^(-11)

Whether it can complex or not depends on the pH of the water it is in. It can reach selectivities of as high as 1028 in neutral or basic solution for some transition metals.

Interactions between pH, complexing and ion exchange components in ground water, sea water, soil, interstitial water and ions, metals, and gases are responsible for many complex interactions.

Clays are used to line waste dumps because of their excellent ion exchange capacity and high affinity for transition metals.

Complexing agents can bioaccumulate because of their high degree of specificity (Hg, Cd, etc).

Natural reactions are complex and rely on many factors such as pH, hydration (water content), activity (concentration), buffer capacity etc.

Notes Table of Contents

Introduction to Environmental Science Home Page

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Created and maintained by
Jim Ferguson
Revised 8/15/95.