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Water - PowerPoint PPT Presentation

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Water. Importance of Water. More than 70% of our total body weight is water Necessary for photosynthesis H becomes incorporated into organic compounds Oxygen released for us to breathe Solvent for most biochemical reactions Important reactant/product. Water is a polar molecule.

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importance of water
Importance of Water
  • More than 70% of our total body weight is water
  • Necessary for photosynthesis
    • H becomes incorporated into organic compounds
    • Oxygen released for us to breathe
  • Solvent for most biochemical reactions
  • Important reactant/product
water is a polar molecule
Water is a polar molecule
  • Due to differences in electronegativities, water is slightly charged at its poles
    • Oxygen takes on a slight – charge
    • Hydrogens take on a slight + charge
  • http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html
hydrogen bonding
Hydrogen Bonding
  • Water can form H-bonds with up to 4 neighboring water molecules
it is water s polarity that gives it many of its unique properties
It is water’s polarity that gives it many of its unique properties
  • Less dense as a solid than a liquid
  • Universal solvent
  • Adhesion and cohesion
    • Capillary action
    • Surface tension
  • High heat of vaporization
  • High specific heat
water is the universal solvent
Water is the universal solvent
  • Water can dissolve many hydrophilic substances
    • Ionic compounds
    • Other polar compounds
  • Form “spheres of hydration”
  • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf
Some substances do not dissolve readily in water
  • Hydrophobic – “water-fearing”
  • Non-polar substances like lipids
  • Water molecules have a strong tendency to stick to one another
  • Cohesion allows water to have a high degree of surface tension
    • Any force is transmitted to the column of water as a whole
  • Ability of water to stick to other substances, esp. charged atoms or molecules
  • Together, cohesion and adhesion allow for capillary action
how unique is water
How Unique is Water??
  • Water is one of only 3 naturally occurring inorganic liquids (mercury and ammonia)
  • Only chemical compound that exists in all 3 states—solid, liquid, and gas
  • Extremely large liquid range (0oC - 100oC)
  • Expands, becomes less dense as a solid
water s 3 states differ in the degree of h bonding

Water’s 3 states differ in the degree of H-bonding


liquid water has
Liquid water has
  • H-bonds that form and break constantly
  • http://www.stolaf.edu/people/giannini/flashanimat/water/water.swf
  • Allows water to have a high specific heat
    • Amount of energy required to raise temp of 1 g 1o C
    • 1 cal/1 g
water vapor
Water Vapor
  • As water moves from liquid to gaseous state, H-bonds are broken, allowing water molecules to escape
  • Water has a high heat of vaporization:
    • It takes 540 cal for 1 g of water to move from liquid to gaseous state
  • Allows for evaporative cooling
    • As fast-moving liquid water molecules escape as vapor, they take their heat energy with them
  • Solid water is less dense than liquid water, allowing it to float
acids and bases
Acids and Bases
  • Water molecules have slight tendency to ionize:

H2O < -- > H+ + OH-

  • The H+ then joins another water molecule resulting in H3O+ (hydronium)
  • The pH scale is a measure of hydronium concentration expressed in moles/liter
ph scale
pH scale
  • http://www.johnkyrk.com/H2O.html
  • pH = -log10[H+]
  • Acids are proton donors
    • Increase the # of H+ ions
  • Bases are proton acceptors
acid base salt
Acid + Base  Salt
  • Acid = H+ + anion
  • Base = OH- + cation
  • H+ joins with OH- to get H2O
  • Anion can combine with cation to make a salt
  • Ex. HCl + NaOH  H2O + NaCl
  • Substance(s) that resist pH changes when an acid or base is added
  • Usu. weak acid or base, do not completely ionize
  • Example: Blood in Vertebrates
CO2 + H20 < -- > H2CO3< -- > H+ + HCO3-
  • Will stay at dynamic equilibrium unless stressed
  • If add excess H+ system shifts left and forms carbonic acid
  • If add OH- they combine with H+ forming water, system shifts right
  • http://www.tvdsb.on.ca/westmin/science/sbioac/biochem/buffer.htm
  • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/buffer12.swf