Properties of Water

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• Properties of Water

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Water content of selected organism and foods
of mass of mass
Marine invertebrates 97 Broccoli 90
Human fetus (1 month) 93 Milk 88
Fish 82 Apples 85
Human adult 70 Grapes 80
Eggs 75
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Distribution of Water on the Earth
Only a small percentage (lt3) of water on Earth
is fresh water. Lakes and rivers account for just
0ver 0.1 of the earths total water
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Global water use (1900-2000)
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Hydrologic cycle
Evaporation Transpiration Condensation Precipitati
on
Processes that cycle water between air and earth
surface
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Evaporation and transpiration
Transpiration is a process in which water escapes
through the pores on leaf surfaces.
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Composition of natural waters

• Fresh water dissolved solids lt0.1.
• Drinking water standard dissolved solids lt0.05
• Major constituents Ca2, Mg2, HCO3-.
• Sea water dissolved solids 3.5 (Dead sea 25)
• Major constituents
• Cl- 19,000 ppm Na 10,600 ppm
• SO42- 2,600 ppm Mg2 1,300 ppm
• HCO3- 140 ppm Ca2 400 ppm
• Br- 65 ppm K 380 ppm

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Water as solvent and as ecosystem

• Water is a remarkable solvent,
• dissolves and transports a wide range of
  materials.
• Interacts with soil and particles and gases in
  the air
• Water houses ecosystems.
• A large percentage of the biosphere lives in some
  form of aqueous environment.
• Water quality is often defined in terms of the
  ability of the aqueous environment to support the
  normal range of biological species.

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Water molecule and hydrogen bonding
H-bonds have a profound effect on the physical
properties of water in both its liquid and solid
states.
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Boiling point and melting point
Without H-bonds, water would be a gas at the
temperature found on earth, and our form of life
and environment would not be possible.
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Heat capacity

• Heat capacity is the amount of heat required to
  raise the temperature of a given mass by 1oC.
  Unit cal/oC/g
• Water has the highest heat capacity of any common
  liquid or solid.
• H2O Cp 1 cal/oC/g
• Alcohol 0.535 cal/oC/g
• Acetone 0.506 cal/oC/g
• Sulfuric acid 0.411 cal/oC/g
• Benzene 0.389 cal/oC/g
• Carbon tetrachloride 0.198 cal/oC/g
• Mercury 0.03346 cal/oC/g

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Heat capacity Implication

• The same amount of heat absorbed or released by
  water causes smaller temperature change than
  other substances.
• The oceans absorb heat from the sun in summer,
  and release it in the winter without causing
  dramatic temperature change.
• Without water absorbing and releasing heat, daily
  and season temperatures on the earth would
  fluctuate as drastically as they do on the
  waterless moon and the planet Mercury. (where T
  fluctuates by hundreds of degrees during the
  light-dark cycle).
• Stabilize temperatures of organisms

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Why coastal cities have mild climate? Heat of
fusion and vaporization

• Heat of fusion the amount of heat required to
  convert 1g of solid to a liquid at its melting
  point.
• Heat of vaporization the amount of heat required
  to convert 1g of a liquid to a vapor at its
  boiling point.
• H-bonds make the heat of fusion and heat of
  vaporization for water higher than for
  practically any other substances.
• In summer, water evaporates from the surfaces of
  oceans and takes heat energy from the surrounding
  land. ? the nearby land mass is cooled.
• In winter, water vapor condenses and releases
  heat to the surrounding ? temperature of the
  surrounding air is raised.

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Temperature-density relationship

• Water has the maximum density at 4oC
• Thats why ice floats on the water surface,
  reducing heat loss from the water under the ice.
• If water trapped in cracks in rocks freezes, the
  force of expansion would split the rock, an
  important process in the weathering of rock.

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Summary Important properties of water
Property Effects and significance
Excellent solvent Transport nutrients and waste products, making biological processes possible in an aqueous medium
Maximum density at 4oC Ice floats
Higher heat of vaporization than any other material Determines transfer of heat and water between the atmosphere and bodies of water
Higher heat of fusion than any other liquid except ammonium Temperature stabilized at the freezing point of water
Higher heat capacity than any other liquid except ammonia Stabilization of temperatures of organisms and geographical regions
Transparent to visible and longer-wavelength fraction of UV light Allow light required for photosynthesis to reach considerable depth in bodies of water
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Study questions

1. On a global scale, what type of water use in
   human society demands most water?
2. What are the major processes transporting water
   between air and earth surface?
3. Summarize the important physical properties of
   water and their significances to the environment.