Properties of Water

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Properties of Water
2
Objectives

• 3.1.4 Draw and label a diagram showing the
  structure of water molecules to show their
  polarity and hydrogen bond formation.
• 3.1.5 Outline the thermal, cohesive, and
  solvent properties of water.
• 3.1.6 Explain the relationship between the
  pro- perties of water and its uses in living
  organisms as a coolant, medium of meta-
  bolic reactions, and transport medium.

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Effects of waters polarity

• Polarity (the effect of having distinct ends, or
  poles) gives water opposite charges on opposite
  ends of the molecule.
• Polarity accounts for all the physical properties
  of water.
• See the video

Electrons shared in a
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Effects of waters polarity

• Polarity (the effect of having distinct ends, or
  poles) gives water opposite charges on opposite
  ends of the molecule.
• In one water molecule, H and O are held
  toge- - ther by covalent bonds (they
  share electrons).
• Weak hydrogen bonds
  form between the H of
  
  one molecule and the
  
  O of another, to a max-
  imum of 4
  bonds.

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Emergent properties of water

• Water has cohesive behavior (holds together).
• Cohesion means it sticks to itself.
• due to hydrogen bonding among molecules.
• aids transport up stems against gravity.
• Water also has adhesion (it clings to other
  substances, such as paper towels) due to
  H-bonds.
• Water has great surface tension due to H-bonds
  it is difficult to break the surface, so it
  forms beads. Some creatures can walk across it.

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Emergent properties of water
A Jesus lizard (or basilisk) using waters
property of surface tension to walk on water
and escape predators.
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Emergent properties of water

• Cohesive and adhesive properties of water
• Adhesion to the side of the glass capillary tube
  pulls water up.
• Cohesion of water
  molecules to them-
  selves pulls
  more
  water molecules along, but
  gravity is also pulling them down, so a
  meniscus forms.

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Emergent properties of water

• Water moves in the xylem of a tree by cohesion,
  adhesion, and evaporation.
• Adhesion is the attraction of one water molecule
  to another kind of molecule (like cellulose).
• Cohesion is the attractive force that one water
  molecule has for another water molecule (due to
  hydrogen bonding).

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Emergent properties of water

• Water resists changes in temperature.
• Has a high specific heat amount of heat that
  must be absorbed to change its temperature by
  1oC.
• To raise 1 g H2O 1oC requires 1 calorie (1
  cal/g/oC)
• Specific heat of ethanol 0.6 cal/g/oC.
• Specific heat of iron 0.1 cal/g/oC (Fe heats
  fast)
• Water heats slowly as energy first goes to break
  the hydrogen bonds, then it heats the molecule.
• Result Bodies of water ( organisms) can absorb
  a lot of solar energy without heating
  dangerously high (H-bonds break before molecules
  heat).

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Emergent properties of water

• A high heat of vaporization cools surfaces as H2O
  vaporizes. A lot of energy is needed to break the
  hydrogen bonds.
• A lot of heat in the ocean is lost as
  water evaporates. I It goes into the
  gas molecule. This energy can
  fuel hurricanes.
• Perspiration absorbs much heat, cools animals and
  plants. (This is called evaporative cooling.)

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Emergent properties of water

• Water expands as it freezes greatest density at
  4oC
• As water cools, more H-bonds form, making a
  crystal lattice. These H-bonds keep the H2O
  molecules separ- ated farther apart than the
  molecules are in liquid water. With more empty
  space, ice is less dense than liquid water, and
  it floats.

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Emergent properties of water

• Water expands as it freezes.
• If ice sank, frozen bodies of water would take
  longer to thaw, making life harder a shorter
  growing season.
• Surface ice in- sulates water
  beneath, keep- ing it a bit
  warmer.

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Emergent properties of water

• Water is a versatile solvent (the solvent of
  life).
• Positive, negative
• ends of water pull
• anions and cations
• from ionically
• bonded materials.

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Emergent properties of water

• Water is a versatile solvent (the solvent of
  life).
• Waters charged ends also coat polar sugars,
• proteins, other molecules, pulling
• them into solution.

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Emergent properties of water

• Water is a versatile solvent (the solvent of
  life).
• Hydrophilic (Gr.- water loving) Substances with
  an affinity for water - they either dissolve in
  or absorb water.
• Ex. sugar, salt, cotton, cellulose.
• Hydrophobic (Gr.- water fearing) Substances
  that dont dissolve in or absorb water.
• Ex. things with many non- polar bonds (esp.
  C-H), such as vegetable oil.

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Emergent properties of water

• Dissociation of water molecules
• In pure water, only 1 molecule of H2O dissociates
  in every 554,000,000 so the concentration of
  each ion (H and OH-) is 10-7 Molar, at 25oC.
• pH the negative log of concentration 7.

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Emergent properties of water

• The pH scale
• In any solution, the
• product of HOH-
• 10-14 M2.
• In a neutral solution, where H OH-,
• 10-7 M x 10-7 M 10-14
• Scale goes from 0 to 14
• pH -log10 H

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Emergent properties of water

• The pH scale
• A pH scale measures concentration of H ions.
• What is H concen- tration
  at pH 1?
• What is H concen- tration at
  pH 2?
• How much more H at pH1 than at
  pH 3?
• How much more H at pH 3 than at
  pH 6?

10 0.1 0.0001 0.0000001 .1 .001
.000001 .000000001
pH paper shows H concentration
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Water in living systems

• Because of waters properties (due to hydrogen
  bonding), in living creatures water is useful in
  many ways.
• As a coolant homeostasis - evaporative cooling
• As a solvent it provide a medium in which
  chemicals can come together and react
  metabolism.
• Due to adhesion and cohesion and solvent
  capa- bilities, it transports chemicals
  throughout the body, which is 65 water (in
  blood, which is 80 water, in urine, etc.).

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Water in living systems

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Water in living systems
Diet water only one H instead of two.