Unique properties of water overview
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Transcript of Unique properties of water overview
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The Water Planet
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• 97% of all water on our planet is in the oceans.
• Fresh water represents the remaining 3% (2/3 is snow and ice in glaciers / polar ice caps).
• Liquid and solid water cover roughly 3/4 of Earth's surface area.
• 29% of the earth’s surface is above sea level (71% is below )
• 97% of all water on our planet is in the oceans.
• Fresh water represents the remaining 3% (2/3 is snow and ice in glaciers / polar ice caps).
• Liquid and solid water cover roughly 3/4 of Earth's surface area.
• 29% of the earth’s surface is above sea level (71% is below )
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Unique properties of water
• Absorbs or releases more heat than most other substances for every temperature degree of change
• Water is a good solvent and can dissolve more substances than other fluids, even rocks
• Water exists in 3 physical states that can power thunderstorms/hurricanes and help transport the sun's energy, nutrients, and organisms
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More than half the world's population live within 60km of a coastline
South Florida, USA
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Overview
• Chemical properties of water– H bonds– Ice– Salinity and Sources
• Physical properties of water– Biomechanics– Density– Temperature
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Chemical properties of water
A. Hydrogen Bonds
B. Crystalline Structure
C. Surface Tension
D. Tensile Strength
E. Specific Heat F. EvaporationG. Molecular InteractionsH. Movement and Transport
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Chemical properties of water
A. Hydrogen Bonds
B. Crystalline Structure
C. Surface Tension
D. Tensile Strength
E. Specific Heat F. EvaporationG. Molecular InteractionsH. Movement and Transport
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Hydrogen Bonds
O
H H
d-
d+ d+
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Hydrogen Bonds
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Hydrogen Bonds
WATER VAPORWATER VAPOR
3 physical states of water:
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Crystalline Structure
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Crystalline Structure
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Ice
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Surface tensionWater has high surface tension due to lateral and downward attraction between individual molecules, which stretches the water's surface, creating a thin skin
O
H H
d-
d+ d+
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Surface tensionWater has high surface tension due to lateral and downward attraction between individual molecules, which stretches the water's surface, creating a thin skin
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Surface tension
• Water striders can walk upon the water's surface.
• Members of the neuston depend upon the surface film of water for transport and food.
• Liquid water on surfaces to which it does not adhere well "beads-up."
• Surface tension of the water allows wind to push against it, generating waves in large water bodies.
• [Detergents reduce the surface tension of water (by as much as 70%) and allows it to spread out on a surface.]
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Tensile strength
Water is strong under tension.
The force needed to pull pure water apart can be as much as 3 x 107 Newtons/m2
120 lbs = 530 Newtons
Limpet attachment strength = 1 x 106 Newtons/m2
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Specific heat
Water can absorb a great deal of energy which goes to breaking hydrogen bonds but does not lead to measurable temperature increases.
Because of the massive number of hydrogen bonds in water, it requires a lot of energy to see even a small change in water temperature.
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Evaporation
A water molecule makes the transition from a liquid phase into a gas phase.
Because the escaping molecule had a higher than average energy level, it leaves the liquid cooler (lower in energy) upon evaporation.
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Hydrogen Bonds - Summary
• High heat capacity (1 cal/g/°C);• Heat of vaporization (540 cal/g);• Heat of fusion (-80 cal/g);• Solid less dense than liquid phase;• High surface tension
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Molecular interactions
Solutes
Dissociation of Water Molecules
KD = [H+][OH-]/[H2O] = 1.8 x 10-16 M
where KD is the dissociation constant
(equilibrium constant) for the dissociation of a proton from a water molecule (the smaller the KD, the stronger the binding)
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pH of solutions
pH - an index of the relative concentration of H+ ions in solution
[H+] = [OH-] = 10-7 M in pure water ([H2O] = 55 M)
pH º -log10[H+]
In pure water, pH = 7
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pH of solutions
• The pH scale ranges from 0 to 14• The higher the pH, the lower the [H+]
(alkaline, basic solutions have a high pH)• The lower the pH, the higher the [H+]
(acidic solutions have a lower pH)
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pH of solutions
Examples:
Gastric juice = 1.0 Seawater 8.0
Orange juice = 4.3 Urine = 6-8.0
Blood plasma = 7.4 Ammonia = 12.0
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pH and the sea
• A difference in pH from 8 to 7.8 can significantly decrease coral growth rates
• Increased CO2 in the atmosphere lowers pH
• Active photosynthesis and nitrogenous waste excretion can increase local pH
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Water as a polar solvent and Salinity
Strong Electrolytes (substances that dissociate completely when dissolved in water - ions)
Salts consist of ions:
NaCl ® Na+ + Cl- salt
HCl ® H+ + Cl- strong acid
NaOH ® Na+ + OH- strong base
For strong electrolytes, KD » ¥
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Water as a polar solvent
Weak Electrolytes (substances that dissociate in water only to a small extent (KD » 10-3 M to 10-
11 M)
H2CO3 H+ + HCO3- KD = 1.7 x 10-4 M
KD » 10-3 M to 10-11 M
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Carbon dioxide-carbonate equilibrium
CO2(aq) + H2O(l) H2CO3(aq) (Carbonic acid)
CaCO3(s) + 2 H+(aq) Ca2+(aq) + H2CO3(aq)
H2CO3 H+ + HCO3
- KD = 4.2 × 10-7
HCO3- H+ + CO3
2- KD = 4.8 × 10-11
CO2(g) CO2(aq) (CO2 from the atmosphere dissolves into seawater)
bicarbonate
carbonate
\ High CO2= low [CO32- ]
Ocean acidification
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Water as a polar solvent
Because of its small size and polar nature, water dissolves many materials, more than any other liquid
Oceans of water act as sink for CO2 molecules – leads to acidification
Seawater contains almost every known naturally occurring element
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Seawater constituents
Component Concentration Percentage of Salinity
chloride 18.98 55.03
sodium 10.56 30.59
sulfate 2.65 7.68
magnesium 1.27 3.68
calcium 0.40 1.18
potassium 0.38 1.11
bicarbonate 0.14 0
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Seawater constituents
• Average ocean water has a salinity of 35.0
• This means that 1000 g of average seawater contains 965 g of water and 35 g of salts.
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Seawater constituents
Dissolvedchemicals
Sediments
Eroded rock particles
Volcanic ash and igneous rocks
on land
Wind, water, andice erosion
River and wind transport and deposition
Sedimentary rock on oceanic crust
Sedimentary rock on land
Biological uptake, or absorption of
particles, or precipitation
Wind, water, andice erosion
Fallout of volcanicash over oceans
Compaction andwater loss Subduction, melting,
and vulcanism
Scraped of and upliftedot subduction zone
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Seawater constituents
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Movement and Transport
Diffusion – high concentrations low concentration
Air vs. water
Mass transport – particles carried by fluid flow
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Diffusion
high concentration low concentration
C = concentrationD = diffusion coefficientx = lengtht = time
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Mass Transport
high concentration low concentration
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Physical properties of water
•Viscosity•Reynolds number, Boundary Layers, and Mass transport
•Density •Temperature
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Water as a fluidFluid (flu·id) French fluide, from Latin fluidus, from fluere to flow; akin to Greek phlyzein to boil over): having particles that easily move and change their relative position without a separation of the mass and that easily yield to pressure; capable of flowing.
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What is a fluid?
Viscosity (m): the resistance of a fluid to motion or internal friction
Reynolds number (Re): the ratio of inertial forces to viscous forces in a fluid
Density (r): the mass of a substance per unit volume
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ViscosityThe viscosity of liquids can vary drastically and decreases rapidly with an increase in temperature.
m = 1 x 10-3 N s/m2m = 50 N s/m2At 20º C
At 100º Cm = 0.07 N s/m2
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Reynolds number
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Reynolds number
Re = rUx/m
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Reynolds number
Re = rUx/m
Re = 1
Re = 108
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Copepod swimmingLow Re
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Boundary Layers and Mass Transport
Re = 101
Laminar Turbulent
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Boundary Layers
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Boundary Layers and Mass Transport
Re = 103
Re = 108
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Density
the mass of a substance per unit volume
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Temperature
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Temperature
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Thermoclines