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Earth’s Biological Medium

WATER. Earth’s Biological Medium. Polarity. Slight charge on either end of the molecule due to the unequal electronegativities of hydrogen & oxygen This leads to many other properties…. Cohesion. http://www.ccs.k12.in.us/chsBS/kons/kons/chemical_and_physical_propertiesanswer.htm.

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Earth’s Biological Medium

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  1. WATER Earth’s Biological Medium

  2. Polarity • Slight charge on either end of the molecule due to the unequal electronegativities of hydrogen & oxygen • This leads to many other properties…

  3. Cohesion http://www.ccs.k12.in.us/chsBS/kons/kons/chemical_and_physical_propertiesanswer.htm • Water molecules stick together with Hydrogen bonds www.biology.arizona.edu http://www.arroyoseco.org/conservation.htm

  4. Adhesion • Water molecules stick (adhere) to other surfaces en.wikivisual.com www.ccs.k12.in.us

  5. news.bbc.co.uk/.../photo_galleries/4670308.stm Surface Tension • Measure of how difficult it is to stretch or break the surface of a liquid • Very high for water http://faculty.vassar.edu/suter/1websites/bejohns/mateselection/files/female.htm

  6. Surface Tension That's gonna leave a mark! www.ext.vt.edu

  7. Specific Heat • Amount of heat that must be absorbed or lost for 1g of a substance to change by 1oC • Water has high specific heat – it resists temperature change • This keeps the earth within viable temperature limits. www.michigan.org

  8. www.doggonesafe.com/dog%20communication.htm Evaporative Cooling • A higher heat of vaporization allows a surface to be cooled as water sits on its surface AP Photo/Darin Cummings

  9. www.astrobiology.com/lter/album01/179.html Density of Ice • Solid water is less dense than its liquid because as hydrogen bonds freeze, they force molecules further apart • In large bodies of water, a top layer of ice actually insulates the water below • 4oC is when water is at its most dense http://www.astrobiology.com/lter/album01/209.html

  10. Universal Solvent • Water dissolves many materials creating aqueous solutions (water is solvent, what’s being dissolved is solute) • This property is the direct result of water’s polar structure • Hydrophilic – substances attracted to water • Hydrophobic – repel water (or not attracted)

  11. Water & pH • In pure water, even if dissociation occurs, the concentration of H+ and OH- ions is equal • When acids or bases are added to water, these concentrations change quickly • pH is a measure of hydrogen ion concentration on a scale between 0-14

  12. Acids • The more acidic, the lower the pH • pH < 7 • Taste sour www.elmhurst.edu

  13. Bases • The more basic, the higher its pH value • Taste bitter community.tvguide.com www.chemistryland.com

  14. Neutralization • When bases and acids of similar strength are combined, the pH of the solution will approach neutral (pH 7) • Water is often a product of a neutralization reaction. Acid + Base --> Salt + Water

  15. Buffers • Substances that resist changes in pH • Many of these in the body since even minor changes can be life threatening • EX: blood ph is 7.4 I am H20

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