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Water Chemistry

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Meniscus: curve at the surface of a liquid. If cohesion is stronger than adhesion, meniscus is convex (like mercury) Mercury. Water ... – PowerPoint PPT presentation

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Title: Water Chemistry


1
Water Chemistry Properties of Water
2
Water statistics
(why understanding it is important!)
  • Covers 75 of Earths surface
  • 97 oceans
  • 3 freshwater
  • 2 in ice caps and glaciers
  • 1 in lakes, underground aquifers, or in
    atmosphere
  • Makes up 70 of the human body
  • 92 of blood plasma
  • 80 of muscle tissues
  • 60 of red blood cells

3
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4
lt 0o C - ice 0o C - 100o C liquid gt
100o C - steam
5
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6
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7
Water is a Polar Molecule -has oppositely
charged ends
  • Water consists of an oxygen atom bound to two
    hydrogen atoms by two single covalent bonds.
  • Oxygen has unpaired paired electrons which
    gives it a slightly negative charge while
    Hydrogen has no unpaired electrons and shares all
    others with Oxygen
  • Leaves molecule with positively and negative
    charged ends

8
Water molecules form Hydrogen bonds
slightly positive charge
hydrogen bond between () and (-) areas of
different water molecules
slightly negative charge
9
Waters Properties
  • Cohesion
  • Adhesion
  • Capillarity
  • High Specific Heat
  • Latent Heat of Vaporization
  • Latent Heat of Melting
  • Latent Heat of Sublimation
  • Latent Heat of Fusion
  • Solid water (ice) is less dense than liquid
  • Universal Solvent
  • Transparent

10
Cohesion
  • Water clings to polar molecules through hydrogen
    bonding
  • Cohesion refers to attraction to other water
    molecules.
  • responsible for surface tension
  • a measure of the force necessary to stretch or
    break the surface of a liquid

11
Adhesion
  • Adhesion refers to attraction to other
    substances.
  • Water is adhesive to any substance with which it
    can form hydrogen bonds.

12
Cohesion Adhesion
  • For water, adhesion is stronger than cohesion
  • Meniscus curve at the surface of a liquid
  • If cohesion is stronger than adhesion, meniscus
    is convex (like mercury)

Capillary action combo of adhesion cohesion
that shows how water is transported in plants
(ex 200 from roots to needles in a California
sequoia)
13
Capillary action
water evaporates from leaves transpiration
adhesion, cohesion and capillary action
water taken up by roots
14
  • trees have specialized structures to transport
    water xylem and phloem plumbing
  • water molecules are dragged from the roots to
    the top of the tree by capillary action and
    cohesion hydrogen bonds help water molecules to
    each other

15
Adaptations of Aquatic Plants/Macrophytes to
Viscosity
  • How have aquatic macrophytes have adapted to
    emergent life?

16
High Specific Heat
  • High specific heat
  • Amount of heat that must be absorbed or expended
    to change the temperature of 1g of a substance 1o
    C.
  • The specific heat of water is 1 calorie/gram C
    4.186 joule/gram C which is higher than any
    other common substance.

17
Impact of waters high specific heat ranges from
the level of the whole environment of Earth to
that of individual organisms.
  • A large body of water can absorb a large amount
    of heat from the sun in daytime and during the
    summer, while warming only a few degrees.
  • At night and during the winter, the warm water
    will warm cooler air.
  • Therefore, ocean temperatures and coastal land
    areas have more stable temperatures than inland
    areas.
  • The water that dominates the composition of
    biological organisms moderates changes in
    temperature better than if composed of a liquid
    with a lower specific heat.

The Earth is over 75 water!
18
Latent Heat of Vaporization
  • High heat of vaporization
  • Amount of energy required to change 1g of liquid
    water into a gas (586 calories).
  • large number of hydrogen bonds broken when heat
    energy is applied

19
  • As a liquid evaporates, the surface of the liquid
    that remains behind cools - Evaporative cooling.
  • Evaporative cooling moderates temperature in
    lakes and ponds and prevents terrestrial
    organisms from overheating.
  • Evaporation of water from the leaves of plants or
    the skin of animals removes excess heat.

20
Thermal Inertia
  • High specific heat of water can have large
    affects on climate conditions of adjacent air
    land masses.
  • Can you provide any examples?

21
Latent Heat
  • Latent Heat of Melting amount of heat required
    to change ice to liquid water (79.72 cal g-1).
  • Latent Heat of Evaporation disruption of
    hydrogen bonding on evaporation of water (540 cal
    g-1).
  • Latent Heat of Sublimation direct sublimation
    of ice to water (679 cal g-1)..
  • Latent Heat of Fusion fusion of molecules of
    0C water to ice (79.72 cal g-1)..
  • B/C of these properties, large energy inputs are
    required to melt ice in the spring, and large
    energy losses due to ice cover in winter.

22
Universal Solvent
  • A liquid that is a completely homogeneous mixture
    of two or more substances is called a solution.
  • A sugar cube in a glass of water will eventually
    dissolve to form a uniform mixture of sugar and
    water.
  • The dissolving agent is the solvent and the
    substance that is dissolved is the solute.
  • In our example, water is the solvent and sugar
    the solute.
  • In an aqueous solution, water is the solvent.
  • Water is not really a universal solvent, but it
    is very versatile because of the polarity of
    water molecules.

23
  • Water is an effective solvent as it can form
    hydrogen bonds.
  • Water clings to polar molecules causing them to
    be soluble in water.
  • Hydrophilic - attracted to water
  • Water tends to exclude nonpolar molecules.
  • Hydrophobic - repelled by water

24
  • Water transports molecules dissolved in it
  • Blood, a water-based solution, transports
    molecules of nutrients and wastes organisms
  • Nutrients dissolved in water get transported
    through plants
  • Unicellular organisms that live in water absorb
    needed dissolved substances

25
Solid water (ice) is less dense than liquid
  • Ice is less dense than water the molecules are
    spread out to their maximum distance
  • Density mass/volume

same mass but a larger volume
26
Oceans and lakes dont freeze solid because ice
floats
  • water expands as it solidifies
  • water reaches maximum density at
    4-degrees C (3.94?C)
  • water freezes from the top down
  • organisms can still live in the water underneath
    the ice during winter

27
Water is Transparent
  • The fact that water is clear allows light to pass
    through it
  • Aquatic plants can receive sunlight
  • Light can pass through the eyeball to receptor
    cells in the back

28
Water Viscosity
  • Far greater than viscosity of air inversely
    proportional to temp.
  • Do you think viscosity and buoyancy of water has
    helped org. adapt to aquatic environment? Why or
    why not?
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