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Properties of Water

Properties of Water. Water: 2 atoms of hydrogen, one of oxygen Held together by strong, covalent bond - electrons are ‘shared’ Water molecules interact – attracted to each other due to electrically charged regions – weak bonds (Hydrogen bonds) formed.

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Properties of Water

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  1. Properties of Water

  2. Water: • 2 atoms of hydrogen, one of oxygen • Held together by strong, covalent bond - electrons are ‘shared’ • Water molecules interact – attracted to each other due to electrically charged regions – weak bonds (Hydrogen bonds) formed

  3. Bonds formed between water molecules – break and reform – like velcro

  4. Properties of Water – Due to interactions between molecules • Liquid at room temperature • Solvent for polar + ionic molecules – due to its own polar nature • Water is cohesive • Has high specific heat – requires a lot of heat to change its temperature • High heat of vaporization • Solid water (ice) floats • Properties altered by dissolved substances

  5. Fig. 3.12 Cohesion of Water

  6. Life in water influenced by: • Dissolved nutrients • Dissolved salts – salinity • Dissolved oxygen • pH • Light • Temperature

  7. pH and water – acids and bases • Due to dissociation of water molecules into Hydrogen and hydroxyl ions • pH is a measure of hydrogen ion concentration • Impacted by dissolved substances – organic materials, gasses, salts

  8. Acids and Bases Pure water dissociates to yield equal amounts of H+ and OH- solution: H2O  OH- + H+ hydroxide hydrogen ion ion

  9. Acids and Bases • Acid: excess of H+ ions • Base: excess of OH- ions pH is a measure of H+ ion concentration on a log scale: pH = -log [H+] • lower number indicates a higher hydrogen ion concentration or a more acidic condition

  10. Buffers • A buffer is a substance that when dissolved in water contributes H or OH ions as needed to resist large changes in pH • sort of like a chemical shock absorber • Important in living systems – pH is critical to maintenance of life processes

  11. Carbon Dioxide acts as an important How carbon dioxide acts as an important natural buffer - how it works: • water absorbs CO2 from atmosphere – how it works: Carbon Dioxide Dissolves in water To form carbonic Acid carbonic Acid dissolves to yield H+ ions All reactions are reversible – if more H+ ions are added reaction pushed to left, more OH- ions reaction pushed to right

  12. CO2 is absorbed from atmosphere • Enters rain water and diffuses directly into surface waters • Creates moderately acidic condition but also some buffering capacity • Other atmospheric gasses may increase acidity of rain water: = acid rain • Sulfur oxides  sulfuric acid • Nitrogen oxides  nitric acid • Strong acids, overcome buffering capacity, create acidic bodies of water • Particular problem for areas with granite substrate

  13. Penetration of Water by Light • % of surface light at various depths: • varies with turbidity – assume clear water • Different wavelengths penetrate water to different degrees – blue penetrates the furthest

  14. http://staffwww.fullcoll.edu/tmorris/elements_of_ecology/images/light_spectral_absorption_water.jpghttp://staffwww.fullcoll.edu/tmorris/elements_of_ecology/images/light_spectral_absorption_water.jpg

  15. Estimation of turbidity of water using senchi disc Turbidity is a function of suspended plankton growth and amount particulate matter in water

  16. Viscosity of Water • 100X that of air • Means movement through water meets considerable resistance • Adaptations of reverse streamlining • Short, blunt anterior • Rapidly tapering body – minimizes replacement of water immediately behind moving animal

  17. Water has a high specific heat • Large amounts of heat exchange required for change in temperature • Temperature slow to change – relative to atmosphere • Cells/organisms composed largely of water, slower to change temp. than atmosphere • Acts as effective heat sink • High heat loss by organisms to surrounding environment • Large amounts of heat required to change state – eg. liquid to solid

  18. Changes in density with temperature • Greatest density at 4C • Ice floats – expands due to intermolecular interactions • Develops layers of stratification • Surface waters warmed (in summer) • Deeper waters cool • Thermocline – region of rapid change in temp. with depth

  19. Oxygen in Water • Dissolves in water from atmosphere • Enters and moves by diffusion • solubility function of • Temperature – greater at lower temperatures • Salinity – more soluble in fresh water • Atmospheric pressure

  20. Oxygen and Depth • Dissolves at surface • Reaches minimal concentration between surface and ~ 1000 meters depth • Produced by photosynthetic activity • Absorbed by metabolic processes • Anoxic or Anaerobic – without oxygen • Certain deep waters • Consequence of metabolic activity

  21. Summary • Life on earth depends on water and its properties • Water is a polar compound • Ends of each molecule have different charges • Water is a solvent for ionic solids – salts which dissociate into positively and negatively charged ions • pH is a measure of H+ ion concentration • Lower pH means higher H+ ion concentration • Light is quickly absorbed by water meaning is in only available at the surface of bodies of water • Water is much more viscous than air

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