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Properties of Water. Water: 2 atoms of hydrogen, one of oxygen Held together by strong, covalent bond - electrons are ‘shared’ Water molecules interact.

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Presentation on theme: "Properties of Water. Water: 2 atoms of hydrogen, one of oxygen Held together by strong, covalent bond - electrons are ‘shared’ Water molecules interact."— Presentation transcript:

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



8 Life in water influenced by: Dissolved nutrients Dissolved salts – salinity Dissolved oxygen pH Light Temperature

9 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

10 Acids and Bases Pure water dissociates to yield equal amounts of H + and OH - solution: H 2 O   OH - + H + hydroxide hydrogen ion ion

11 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


13 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

14 Carbon Dioxide acts as an important How carbon dioxide acts as an important natural buffer - how it works: water absorbs CO 2 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


16 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

17 Penetration of Water by Light % of surface light at various depths: Depth% of surface light 1 cm73 1 meter44,5 10 meters22.2 100 meters0.53 varies with turbidity – assume clear water Different wavelengths penetrate water to different degrees – blue penetrates the furthest

18 s/light_spectral_absorption_water.jpg

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

20 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


22 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

23 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


25 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


27 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

28 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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