Biol361 Lecture 3 (2007):
PHYSICS AND CHEMISTRY OF SEAWATER
- 1) HISTORY OF WATER CHEMISTRY. Empodocles (400 BC) said all matter was composed of 4 primary elements, Aristotle (300 BC) agreed; but Lavoisier (1783) showed water was divisible
- 2) UNUSUAL PHYSICAL AND CHEMICAL PROPERTIES OF WATER DUE TO POLARITY OF MOLECULE: MAKES IT "STICKY"
- asymmetrical alignment of hydrogen atoms in water molecule causes polarity
- covalent bonds- strong bond that shares electrons between atoms
- hydrogen bonds- weak bond due to charge asymmetry between atoms or molecules; (they give clear ocean water it's blue color because they absorb red light preferentially)
- 3) WATER IS A REMARKABLE THERMAL BUFFER:
- its heat capacity, latent heat of melting, & latent heat of vaporization are the highest of common liquids & solids
- these have major consequences for global climate
- 4) WATER IS A REMARKABLE SOLVENT (can dissolve more substances than any other liquid)
- 5) ORIGIN OF SEAWATER AND MEASUREMENT OF SALINITY:
- seawater is not just concentrated river water (ionic proportions differ: excess Cl- and Na+, deficient in Ca+2, CO3-2 and SiO2, in seawater)
- arose initially via outgassing from earth's mantle ('juvenile water'; highly acidic due to excess Cl- and H+); still occurs at 0.1 km3/yr from mid-ocean ridges
- proportions of ions in seawater are remarkably constant worldwide
- salinity can be measured by CHLORINITY (salinity= 1.80655 * chlorinity; chlorinity= concentration of halide ions: Cl, Br, Fl, I), CONDUCTIVITY or SPECIFIC GRAVITY
- salinity of open ocean is 35 g/kg of water= 35 parts per thousand
- 6) EFFECTS OF TEMPERATURE & SALINITY ON SEAWATER:
- increasing temperature has 4 effects: a) increases solubility of ions, b) decreases solubility of gases, c) decreases viscosity, and d) decreases density
- increasing salinity has 4 effects: a) increases density (major effect), b) decreases freezing point, c) decreases rate of evaporation (minor effect), and d) alters temperature of maximum density
For a cool paper modeling how quickly the arrangement of water molecules changes as water freezes see:
- Matsumoto,M. et al. 2002.
Molecular dynamics simulation of the ice nucleation and growth process leading to water freezing.
Nature 416, 409 - 413 (28 March)
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Copyright (c) 2007 by A. Richard Palmer. All rights reserved.
(revised Jan. 16, 2007)