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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