Chemical and Physical Features of Seawater and the World Ocean

“If there is magic on this planet, it is contained in water.”Loren Eiseley

“Well, me don’t swim too tough so me don’t go in the water too deep.”Bob Marley

What is Water ?

Introduction – the stuff covers 70% of the Earth Brainstorming activity Chemical & Physical Properties of Water Categorization activity Defend your categories If time permits… why the answer to life is

104.5º

Chemical & Physical Properties Physical property – properties that describe a

substance without changing the identity of the substance.

Physical change – change that does not result in the production of a new substance, only the appearance of the substance

Chemical property – properties that describe how a substance changes into a completely different substance

Chemical change – change that results in the production of another substance

Common Properties of WaterPhysical Properties Chemical PropertiesCohesion/Surface tensionFound in all three states on the earth

Universal Solvent – dissolves more substances than any other common liquid

Conduction of heat – highest of all liquids (except for mercury)

pH – water dissociates into anions (OH-) and cations (H+)

Latent heat of vaporization – highest of all common substances

Polarity – water has positive and negative ‘ends’

Latent heat of fusion – high for a molecule of its size (melting/freezing)

Hydrophobic effect

Heat capacity – highest of all common solids & liquids

Density – max at 4ºC for pure water

Viscosity –relatively low for a liquid

ReferencesCastellano, A. (2006) “Victoria Beach”Castro, P. & M.E. Huber (2005) Marine Biology, 5th ed. McGraw-Hill Higher

Education, Boston, MA.“Chemical Properties of Water” PlanetWater.au.com Retrieved on Feb 3, 2007

from www.ozh2o.com/index.html“floating water 5” (2006) westerLower, S. (2007) “H2O a gentle introduction to the structure of water.” Retrieved

on Feb 3, 2007 from http://www.chem1.com/acad/sci/aboutwater.htmlNybakken, J.W. & M.D. Bertness (2005) Marine Biology, An Ecological

Approach, 6th ed. Pearson Education, Inc., San Francisco.Perlman, H. (2006) “Water properties” Water Science for Schools. USGS.

Retrieved on Feb 3, 2007 from http://ga.water.usgs.gov/edu/waterproperties.html

Petrucci, R.H. (1982) General Chemistry Principles and Modern Applications, Macmillan Publishing Co. Inc., New York.

The Water Molecule

Two hydrogen atoms, one oxygen atom

H atoms form 105º angle This angle produces an

asymmetrical dipole. Slight (+) charge on the H atoms and slight (-) charge on the O atoms.

O

HH

105º

The Water Molecule These slight charges cause the

(+) H atoms of one water molecule to attract the (-) O atoms of other water molecules.

These weak bonds are called hydrogen bonds.

Water can hydrogen bond with other substances aside from itself.O

H

H

O

HH

O

H

H

Why does ice float? Density-Temperature Relationship

Background Temperature is a measure of kinetic energy (KE). As

KE decreases, hydrogen bonds stay formed and break less. Water molecules stay closer together until…

Explanation As the temperature approaches 4ºC, less dense ice

clusters begin to form in the liquid. At 0ºC when all water molecules become locked in

the rigid ice lattice, the hydrogen bonds actually hold molecules farther apart than at 4ºC. This creates spaces making the water less dense.

Why does ice float? Density-Temperature Relationship Graph

The cohesion or mutual attraction of water molecules creates a flexible barrier on the surface of water.

This helps support aquatic insects such as water striders (Halobates sp.)

How can water bugs “stride” across water without breaking the surface?Surface tension and cohesion

www.nps.gov/olym/insect/gerridae.jpg

Why do fish not get electrocuted when lightning strikes the ocean? Conductivity

Explanation Conductivity is a property that measures the ability of a

substance to transmit heat, electricity, or sound. Pure water is not a good conductor of electricity. Its

conductivity is about 20 dS/m. (Compare with silver – the highest conductivity with 63 x 106 S/m)

In addition, the electrical charge of lightning usually spreads instantaneously along the surface of the water from the location of the strike and to a lesser degree below the surface at the strike site. Fish in other areas are not affected.

Background Heat – energy of molecular motion Water can absorb or give up heat by

conduction (molecular exchange of heat) or convection (mixing)

Explanation Water can hold heat longer and

release heat more slowly than land. Temperature differential between land

and ocean will cause uneven heating of air masses which drive winds and moderate any drastic temperature changes.

Why do coastal areas have slower temperature changes than inland areas?Heat capacity

Off-shore breeze

On-shore breeze

Fats and oils are nonpolar molecules.

These compounds do not have slight regions of charge like water does.

Therefore water molecules are not attracted to nonpolar molecules and actually can be repelled by them.

Basis for cell membranes and the water repellency of marine mammals and birds.

Why don’t fats and oils dissolve in water?Polarity

Because water is polar, it dissolves most substances, especially other polar molecules and compounds composed of ions, atoms or molecules that carry an electrical charge.

These ionic compounds are often called salts.

NaCl (salt) most common dissolved salt in ocean. There are many others.

Seawater is a solution of these salts.

Why does water dissolve more substances than any other common liquid?The Universal Solvent

Salt crystal

SeawaterSources of salts and dissolved solids: Erosion of rocks and soil Solutes released from rivers Breakdown of organisms Condensation of rain from the atmosphere Releases from hydrothermal vents

Seawater is 96.5% water 3.5% dissolved compounds

Salinity

Measured in parts per thousand (ppt) Grams of salt left behind when 1000g of water evaporate

Average value 35 ppt or 35‰ Range from 0‰ near river mouths to 40% in the dead sea. Globally, seawater salinity remains constant. Rule of

constant proportions states that the percentage of various ions in seawater remains constant.

Total amount of dissolved salts in seawater.

Surface Salinities of the Oceans

Dissolved compounds in seawater Inorganic substances (salts, nutrients) Dissolved gases Organic compounds (fats, oils, vitamins,

amino acids, proteins) Nitrates and phosphates (usually in

excess as pollution) Pollution (DDT, PCBs, chlorinated

hydrocarbons that are synthetic)

Dissolved Gases

Primarily nitrogen, carbon dioxide, oxygen N2 biologically inert. CO2 needed for photosynthesis and pH

buffering. O2 required for respiration.

              

                                

Factors that Affect Salinity Salinity increases due to…

freezing of seawater. evaporation.

Salinity decreases due to… melting of icebergs and sea ice. precipitation. run-off from rivers.

pH The amount of hydrogen ions in a

substance is referred to as pH. pH = (pondus hydrogeni or “power of

hydrogen” pH = -log10 [H+] Scales ranges from 0 to 14.

Therefore, a pH of 14 means that the water is very alkaline (basic) while pH 1 means it is acidic. A pH of 7 is neutral.

http://bangordailynews.com/2011/10/07/environment/shellfish-harvesters-plagued-by-acidic-%E2%80%98dead-muds%E2%80%99/

Seawater pH The carbonic acid – bicarbonate – carbonate system

keeps seawater at a pH value between 7.5 and 8.4. The oceans are an enormous “sink” for atmosphere

CO2

The Carbon Buffering System

Seawater has an unusually large capacity to absorb CO2.CO2 + H2O H2CO3 (carbonic acid)

H2CO3 H+ + HCO3 – (bicarbonate ion)

HCO3 – H+ + CO32- (carbonate ion)

Ocean Acidification

http://www.nrdc.org/oceans/acidification/aboutthefilm.asp

http://bangordailynews.com/2011/10/07/environment/shellfish-harvesters-plagued-by-acidic-%E2%80%98dead-muds%E2%80%99/

Work Cited

Kreger, Chris. "Acid Mine Drainage: Alkalinity." Exploring the Environment: Water Quality. 2004. Wheeling Jesuit University. 2 Oct 2008 <http://www.cotf.edu/ete/modules/waterq/wqalkalinity.html>.

Lower, Stephen. "A gentle introduction to water and its structure." H2O. 2008. 1 Oct 2008 <http://www.chem1.com/acad/sci/aboutwater.html>.

"October 2006 Archives." [Weblog The Marine Electronics Weblog] Oct 2006. Panbo . 1 Oct 2008 <http://www.panbo.com/archives/2006_10.html>.

Water Conductivity. 2008. Lenntech Water Treatment & Purification B.V.. 1 Oct 2008 <http://www.lenntech.com/water-conductivity.htm>.

Woodruff, Steve W.. "Water & Weather." Los Angeles Pierce College Weather Station. 1 Oct 2008 <http://data.piercecollege.edu/weather/water.html>.