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CHAPTER 5 Water and Seawater
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Types of Bonding
Water Molecule Formation & Configuration
Unusual Properties
Hydrogen Bonding
Heat Capacity
Phases of Water
Adding Salts to Water
Constituents of Seawater
Sampling Devices
Effects of Density and Salinity
Hydrologic Cycle
Composition of River Water
Residence Times
Dissolved Gases
pH of Seawater
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Covalent Bonding
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Ionic Bonding
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WATER’S UNUSUAL PROPERTIES
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Hydrogen bonding• Polarity means small
negative charge at O end
• Small positive charge at H end
• Attraction between + and – ends of water molecules to each other or other ions
Fig. 5.3
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Hydrogen bonding• Hydrogen bonds are weaker than covalent
bonds but still strong enough to result in:– High surface tension– High solubility of chemical compounds in
water– Solid, liquid, gas at Earth’s surface– Unusual thermal properties– Unusual density
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Surface tensionS
CALORIE
the amount of energy required to raise the temperature of 1 gm of liquid water 1 degree Centigrade
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HEAT CAPACITY (SPECIFIC HEAT)
The amount of energy required to raise the temperature of 1 gm of a substance 1 degree Centigrade
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(liquid)
(ice) 0.5
Granite 0.19**
Quartz 0.19**
**
**
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Soil (average) 0.70
What does this mean?
• If we had 3 cookie sheets each 1 cm deep
• One filled with water, one with soil and one with sand
• The amount of incoming energy that would heat the water 1oC, would
heat the soil 1.4oC and the sand 5oC
Unusual thermal properties of H2O
• Water - high heat capacity– Amount of heat required to raise the
temperature of 1 gram of any substance 1o C
– Water can take in/lose lots of heat without changing temperature very much
– Rocks - low heat capacity• Rocks quickly change temperature as they
gain/lose heat
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Day/Night Temperature DifferencesLarge on land, small in the ocean
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Global thermostatic effects• Moderate temperature on Earth’s surface
– Equatorial oceans (hot) don’t boil– Polar oceans (cold) don’t freeze solid
• Marine effect– Oceans moderate temperature changes
day/night; different seasons
• Continental effect– Land areas have greater range of
temperatures day/night and during different seasons
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Unusual thermal properties of H2O
• H2O has high boiling point• H2O has high freezing point• Most H2O is in the form of water (liquid) on
Earth’s surface (good for life)• High latent (hidden) heats of
– Vaporization/condensation– Melting/freezing– Evaporation
Fig. 5.6
Specific Heat = 1.0calories/ gm
Specific Heat = 0.5calories/gm
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Water molecules in different states of matter
Fig. 5.5
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Show water phase animation
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Changes of state due to adding or subtracting heat
• Heat is energy of moving molecules
• Temperature is measurement of average kinetic energy
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Elements within columns share similar properties
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Ionic bonding, loosely held together
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Dipolar water molecules break ionic bonds bysurrounding sodium and chloride ions
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CONSTITUENTS OF SEAWATER
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Salinity • Total amount of solid material dissolved in water• Typical salinity is 3.5% or 35o/oo• Six elements make up 99% of dissolved solids in seawater
Fig. 5.12
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SALINITY UNITS
% = PERCENT OR PARTS PER HUNDRED (PPH)
Since open ocean salinity varies from 3.3-3.7%, we move the
decimal one place to the right and express it as 0/00 OT PARTS
PER THOUSAND (PPT)3.3-3.7% BECOMES 33-37 o/oo
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Measuring salinity• Evaporation• Chemical analysis
– Principle of constant proportions– Major dissolved constituents in same
proportion regardless of total salinity– Measure amount of chlorine (chlorinity)
• Electrical conductivity– Salinometer– CTD
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Salinity variations• Open ocean salinity 33 to 37 o/oo
• Coastal areas salinity varies more widely– Influx of freshwater lowers salinity or
creates brackish conditions
– Greater rate of evaporation raises salinity or creates hypersaline conditions
– Salinity may vary with seasons (dry/rain)
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> 100 ppm
>1, <100 ppm
< 1 ppm
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Forchammer’s Principle(Rule of Constant Proportions)
Although the salinity of seawater may changefrom place to place, the ratio of ions
to each other remains constant
Importance: You only need to measure one ionto calculate the concentration of others -
this can be the cheapest or easiest one to measure
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How to change salinity
• Add water
• Remove water
• Add dissolved substances
• Remove dissolved substances
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Processes that add/subtract water from oceans
• Precipitation (rain or snow)
• Runoff (river flow)
• Melting icebergs
• Melting sea ice
• Evaporation
• Formation of sea ice
Salinity decreases through:
Salinity increases through:
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Nansenbottle
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Reversing Thermometer - takes only a single measurement
Expendable Bathythermograph (XBT) -
Takes a continuous profile as it falls through the water column
Water-samplingbottles
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Salinity is most commonlymeasured by electrical
conductivity
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Density of water
• Density of water increases as temperature decreases down to 4oC
• From 4oC to 0oC density of water decreases as temperature decreases
• Density of ice is less than density of water
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Density of water
Fig. 5.10
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Freshwater lake
10oC
8oC
6oC
5oC
4oC
8oC
6oC
5oC
4oC
Freshwater lake
6oC
5oC
4oC
Freshwater lake
5oC
4oC
Freshwater lake
3oC
2oC
0oC
1oC
ice
4oC
Freshwater lake
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