Introduction to Water

Created by Dr. Michael Pidwirny, Department of Geography, Okanagan University College, BC, CA

evaporation

Soil and Water

What is Soil?

The interface between the atmosphere, hydrosphere, biosphere and lithosphere

naturally occurring layers of mineral and organic constituents that differ from the underlying parent material in their physical, chemical, and mineralogical properties

Rock

What is Water?

A binary compound that occurs at room temperature as a clear colorless, odorless, tasteless liquid

Freezes into ice below 0 C and boils above 100 C

Necessary for life on earth (human, animals and plants)

Constitutes 60-70 % of the human body

www.atpm.com

1050

Oxygen

Hydrogen Hydrogen Electro positive

Negative

Polarity

Symmetrical (e.g., CO2)

H-O : 0.97 A

H-H : 1.54 A

angstroms

H+

H+

O--= + -H2O

Hydrogen bond

Gives structural strength

Bond depends on temperature:

Bonds are weaker at higher temperature

Positive end attraction with neg. end of other water molecules

http://www.chem1.com/acad/sci/aboutwater.html

Dipolar nature of water due to unevenly distributed charges

O=

H+H+

Polymer type of grouping

Cations: Na+, K+, Ca2+ become hydrated through their attraction to the negative end of water (Oxygen side)

Anions or negatively charged clay surfaces attract water through positive hydrogen side

J. L. Fulton, Y. Chen, S. M. Heald, and M. Balasubramanian, Rev. Sci. Instruments., 75(12), 5228-5231 (2004).

http://www.pnl.gov/cmsd/highlights/images/20050727water.jpg

http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-1/water-structure.jpg

Does water swell and shrink with Temperature?

1

0.998

0.996

0.994

0.992

0.990

-10 0 10 20 30 40 50

De

nsi

ty (

g c

m-3)

Temperature (0C)

40C

www-ssrl.slac.stanford.edu/.../structure_ice.jpg

http://www.columbia.edu/cu/biology/courses/c2005/purves6/figure02-15a.jpg

Representation of Ice Melting

www.cscs.ch/.../representations/index.html

periodsgroups

Dimitri Mendeleev

Temperature range in liquid phase for H2x compounds

100

50

0

-50

-100

0 50Molecular Weight

Te

mp

era

ture

(0C

)

100

H2O

H2S

H2Se

H2Te

Boiling point

Freezing point

Hydrogen sulfide

Hydrogen selenide

Hydrogen telluride

(2+16=18)

(2+32=34)

(80)

(130)

The sum of the atomic weights of all atoms in a molecule

If water were an ordinary compound whose molecules are subject to weak forces, its boiling and freezing points would fall below hydrogen sulfide

Strong hydrogen bonding between water molecules prevents this so that liquid water acts more like a gel, cluster, or polymer

Water occurs in all three states (solid, liquid, and gaseous) at prevailing temperatures on the earth’s surface

Example: Ice cubes in a glass at room temperature

Soil Solution

aqueous liquid phase of the soil and its solutes

Hydrogen Bonding

Water is a powerful solvent

How salt dissolves in water

nutrition.jbpub.com/.../chemistryreview6.cfm

How do plants obtain the nutrients in the soil?

http://www2.mcdaniel.edu/Biology/botf99/nutrition/catex.jpg

www2.mcdaniel.edu/.../botf99/nutrition/soils.htm

Clay minerals as sources of ions

http://www.ca.uky.edu/agc/pubs/agr/agr11/fff00003.gif

Typical ion concentrations (can be much higher in arid regions due to high

evapotranspiration (ET) and concentrating effects)

K+ 1-10 (mg/L)

Na+ 1-5

Ca+2 20-200

Mg+2 2-50

Si+4 10-50

SO4-2 60-300

Cl- 50-500

Solutes exist in solution as:

• Free hydrated ions

• Complexes with ligandsorganic or inorganic

(H2O, NH3+, F-, OH-, Cl-, CN- or

EDTA, citric acid, DTPA, NTA,…)

“Free” hydrated ions

http://www.freepatentsonline.com/7115549-0-large.jpg

Metal-ligand complexes

http://journals.iucr.org/e/issues/2006/11/00/ng2089/ng2089scheme1.gif

Ligand Exchange Mechanisms[ ML6 + Y- ML5Y + L- ]

www.meta-synthesis.com/.../mechanism.html