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Water

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Title: Water


1
Water
  • Sustainer of Life

2
  • Water is unique in that it exists in three
    physical states within the natural environment.
  • Due to the polar-covalent bonds and oxygens high
    electro-negativity, water readily creates
    hydrogen bonds.
  • Every water molecule can
  • form hydrogen bonds
  • with four other water
  • molecules.

3
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4
  • Water has four unique properties that facilitate
    the sustainability of life on Earth.
  • The cohesive behavior of water.
  • The ability of water to stabilize temperatures.
  • The ability of water to expand upon freezing.
  • Water as a universal solvent.

5
Cohesion
  • The glue that holds water together in any form
    is hydrogen bonds.
  • These bonds are relatively weak in liquid
    form.they are very transient in nature. These
    molecules break and form at an extremely rapid
    rate.
  • This is what creates the fluidity and structure
    of water.
  • Collectively, the bonding properties of water are
    known as cohesion.

6
  • Cohesion is the ability for water molecules to
    cling to each other.
  • Related to cohesion, is adhesion.the affinity
    of water to cling to other substances besides
    itself.
  • Classic example The cohesive and adhesive
    properties of water allow for the movement of
    water up the xylem vessels within plants.

7
  • Surface Tension
  • Water has a greater surface tension than most
    other liquids.
  • The orderly arrangement of hydrogen molecules
    at the interface between the water and the air
    creates a stronger skin at the surface of a
    body of water. This surface resists breaking.

8
Temperature Modification
  • Water possesses a high specific heat.
  • This allows water to either absorb or release
    tremendous amounts of heat energy without
    changing temperature.
  • Hydrogen bonding is responsible for this
    phenomena.heat is absorbed to break hydrogen
    bonds and heat is released to create hydrogen
    bonds.

Water 1 Calorie per gram per degree Celsius.
9
What This Means For The EarthAnd You
  • Large bodies of water, like oceans, can absorb
    tremendous amounts of heat energy throughout the
    day without raising the temperature of the water
    significantly. At night
  • this stored heat is released back into the
    atmosphere, thus helping to regulate the
    temperature of the Earth.
  • Since the degree change within water is minimal
    despite the absorption of heat energy, the water
    remains an optimal temperature for marine life.
  • You are primarily water, therefore you also
    have the ability to resist temperature changes.

10
Heat of Vaporization
  • Vaporization The transfer of a liquid to a
    gas.
  • Water has a high heat of vaporization.
  • Hydrogen bonds must be broken before a state
    change will occur.
  • As liquid evaporates, the surface remains cool
    because it is the hottest molecules that escape
    into the atmosphere. (Those with the most
    kinetic energy)
  • Evaporative Cooling
  • Also helps to stabilize the temperature of large
    bodies of water.
  • Is the basis behind sweating to release excess
    body heat.

11
Water Expands When Frozen
  • Weird Water Less dense as a solid than a
    liquid.
  • As water freezes the crystalline structure locks
    the molecules in a fixed lattice that is less
    spread out (hence dense) than liquid water.
    Remember that the bonds in liquid water are very
    transient and constantly shift.
  • This is why ice floats.
  • Ice floating allows for only the surface of
    bodies of water to freeze, effectively insulating
    the water below.protecting delicate life.

12
Water As The Universal Solvent
  • Solution A homogenous liquid mixture of two
    or more substances.
  • Solvent The dissolving agent of a solution.
  • Solute The substance that is dissolved.
  • Aqueous Solution Solution where water is the
    solvent.
  • Water is an excellent solvent due to its
    polarity.

The sphere of water around each dissolved ion is
called the hydration shell.
13
Hydrophilic versus Hydrophobic
  • Hydrophilic Any molecule with an affinity for
    water..whether they dissolve or not.
  • Hydrophobic Non-ionic or non-polar molecules
    tend to repel water.

Hydrophobic interactions are more correctly
called hydrophobic exclusions. In the figure
above and to the left, there are two regions
containing hydrophobic substances. Each of the
substances is excluded from the water matrix.
Over a period of time the two areas of
hydrophobic substances will encounter one
another, combine and form one larger hydrophobic
region that is excluded from the water matix.
This combined state is more energetically
favorable than the one in which the hydrophobic
substances were separate. Thus this combined
state will persist.
14
Dissociation of Water Molecules
  • Hydrogen bonds within two water molecules
    occasionally shift, leaving the electron behind.
  • The water molecule that lost its proton is
    called a hydroxide ion.
  • The water molecule that gained the proton is
    called a hydronium ion.

15
  • This is a reversible reaction that reaches
    equilibrium.
  • Adding particular solutes to water can disrupt
    this equilibrium.
  • Creates acidic and basic solutions.
  • An acid has an excess of hydronium ions.
  • A base has an excess of hydroxide ions.
  • Measured with pH scale.

16
Buffers
  • Substances that minimize the changes in the
    concentrations of H and OH-.
  • Buffers either accept hydrogen ions from acidic
    solutions or donate hydrogen ions to basic
    solutionsthus creating a neutral solution.
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