SEAWATERSEAWATER and the and the

properties of the properties of the water moleculewater molecule

The form of the HThe form of the H22O O molecule determines its molecule determines its behaviorbehavior One hydrogen H and two oxygen O One hydrogen H and two oxygen O

atoms bonded by sharing electronsatoms bonded by sharing electrons Both H atoms make a positive side, Both H atoms make a positive side,

O side is negative, so it is a: O side is negative, so it is a: Polar Polar moleculemolecule

Hydrogen bondingHydrogen bonding Polarity means Polarity means

small negative small negative charge at O endcharge at O end

Small positive Small positive charge at H endcharge at H end

Attraction Attraction between + and – between + and – ends of water ends of water molecules to each molecules to each other or other ionsother or other ions

Fig. 5.3

Effects of hydrogen Effects of hydrogen bonding: bonding: the result of polaritythe result of polarity Hydrogen bonds are weaker than Hydrogen bonds are weaker than

covalent bonds but still strong enough covalent bonds but still strong enough to result in:to result in:1.1. High surface tensionHigh surface tension

2.2. Cohesion and adhesionCohesion and adhesion

3.3. High solubility of chemical compounds High solubility of chemical compounds in waterin water

4.4. Solid, liquid, gas at Earth’s surfaceSolid, liquid, gas at Earth’s surface

5.5. Unusual thermal propertiesUnusual thermal properties

6.6. Unusual density Unusual density

Water molecules in different Water molecules in different states of matterstates of matter

Fig. 5.5

Putting heat in perspectivePutting heat in perspective

Heat is energy of moving moleculesHeat is energy of moving molecules Calorie is amount of heat needed to Calorie is amount of heat needed to

raise the temperature of 1 gram of raise the temperature of 1 gram of water by 1water by 1oo C C

Temperature is measurement of Temperature is measurement of average kinetic energyaverage kinetic energy

Fig. 5.6

Effect of heat input on temperature

Unusual thermal properties of Unusual thermal properties of HH22OO HH22O has high boiling pointO has high boiling point HH22O has high freezing pointO has high freezing point High High latent (hidden) heatslatent (hidden) heats of of

Vaporization/condensationVaporization/condensation Melting/freezingMelting/freezing EvaporationEvaporation

Unusual thermal properties of Unusual thermal properties of HH22OO Water high Water high heat capacityheat capacity

Which is the amount of heat required to Which is the amount of heat required to raise the temperature of 1 gram of any raise the temperature of 1 gram of any substance 1substance 1oo C, also called “ C, also called “specific specific heatheat””

Water can take in/lose lots of heat Water can take in/lose lots of heat without changing temperature muchwithout changing temperature much

Rocks low heat capacityRocks low heat capacity Rocks quickly change temperature as Rocks quickly change temperature as

they gain/lose heatthey gain/lose heat

Specific Heat Values

  Specific Heat

Material (cal/g °C) (J/kg K)

Aluminum 0.215 900

Copper 0.092 385

Iron 0.107 448

Lead 0.031 130

Brass 0.092 385

Magnesium 0.245 1030

Zinc 0.093 390

Styrofoam 0.27 1131

Air 0.240 1006

Water 1.000 4190

Ice 0.500 2095

Global thermostatic Global thermostatic effectseffects

Moderate temperature on Earth’s Moderate temperature on Earth’s surfacesurface Equatorial oceans (hot) don’t boilEquatorial oceans (hot) don’t boil Polar oceans (cold) don’t freeze solidPolar oceans (cold) don’t freeze solid

Marine effectMarine effect Oceans moderate temperature changes Oceans moderate temperature changes

day/night; different seasonsday/night; different seasons Continental effectContinental effect

Land areas have greater range of Land areas have greater range of temperatures day/night and during temperatures day/night and during different seasonsdifferent seasons

Density of water due to Density of water due to temperaturetemperature

Density of water increases as Density of water increases as temperature decreases, until it temperature decreases, until it gets to 4gets to 4ooC to 0C to 0ooC (ice) density of C (ice) density of water decreases as temperature water decreases as temperature decreasesdecreases Density of ice is less than density of Density of ice is less than density of

waterwater

Density of waterDensity of water

Fig. 5.10

Density of Various MaterialsMaterial g/cm3

Aluminum 2.7

Copper 8.96

Iron 7.87

Lead 11.3

Brass 8.4

Magnesium 1.74

Zinc 7.14

Lead 11.3

Water 1.00

Ice 0.917

SalinitySalinity Total amount of solid material dissolved in water- Total amount of solid material dissolved in water- Traditional Traditional

definitiondefinition Typical salinity is 3.5% or 35Typical salinity is 3.5% or 35oo/oo/oo

oo/oo or parts per thousand (ppt) = grams of salt per kilogram of /oo or parts per thousand (ppt) = grams of salt per kilogram of waterwater

g/Kgg/KgSix elements make up 99% of dissolved solids in seawaterSix elements make up 99% of dissolved solids in seawater

Fig. 5.12

Measuring salinityMeasuring salinity Can be measured by specific gravity, Can be measured by specific gravity,

electrical conductivity or by electrical conductivity or by refraction of lightrefraction of light

We will measure with a refractometer We will measure with a refractometer in parts of salt per thousand of water in parts of salt per thousand of water (the unit being ppt or 0/00)(the unit being ppt or 0/00) 2% would be equal to 20 0/002% would be equal to 20 0/00

Salinity variationsSalinity variations Open ocean salinity 33 to 38 Open ocean salinity 33 to 38 oo/oo/oo Coastal areas salinity varies more Coastal areas salinity varies more

widelywidely Influx of freshwater lowers salinity or Influx of freshwater lowers salinity or

creates creates brackishbrackish conditions conditions Greater rate of evaporation raises Greater rate of evaporation raises

salinity or creates salinity or creates hypersalinehypersaline conditions conditions

Salinity may vary with seasons Salinity may vary with seasons (dry/rain)(dry/rain)

Processes that add/subtract Processes that add/subtract water from oceanswater from oceans

Precipitation (rain Precipitation (rain or snow)or snow)

Runoff (river Runoff (river flow)flow)

Melting icebergsMelting icebergs Melting sea iceMelting sea ice

EvaporationEvaporation Formation of Formation of

sea icesea ice

Salinity decreases through:

Salinity increases through:

Deep ocean variation of Deep ocean variation of salinitysalinity

Surface ocean salinity is variableSurface ocean salinity is variable Deeper ocean salinity is nearly Deeper ocean salinity is nearly

the same (polar source regions the same (polar source regions for deeper ocean water)for deeper ocean water)

HaloclineHalocline, rapid change of , rapid change of salinity with depthsalinity with depth

SalinitSalinity y versus versus depthdepth

Fig. 5.22

Hydrologic cycle describes Hydrologic cycle describes recycling of water near Earth’s recycling of water near Earth’s surfacesurface

Fig. 5.15

Surface ocean variation of salinity…Surface ocean variation of salinity…why?why?

Fig. 5.21

Surface ocean variation of Surface ocean variation of salinitysalinity Polar regionsPolar regions: salinity lower, lots of : salinity lower, lots of

rain/snow and runoffrain/snow and runoff Mid-latitudesMid-latitudes: salinity higher, high : salinity higher, high

rate of evaporationrate of evaporation EquatorEquator: salinity lower, lots of rain: salinity lower, lots of rain Thus, salinity at surface varies Thus, salinity at surface varies

primarily with latitudeprimarily with latitude

What else affects What else affects DENSITY DENSITY

(besides salinity)?(besides salinity)?

TEMAPERATURE affects TEMAPERATURE affects DENSITYDENSITY

Density seawater controlled by Density seawater controlled by temperature, temperature, Most important influence is temperatureMost important influence is temperature Density increases with decreasing Density increases with decreasing

temperature, as more molecules can pack temperature, as more molecules can pack tightly when not moving as muchtightly when not moving as much

Ocean layered according to densityOcean layered according to density 1.022 to 1.030 g/cm1.022 to 1.030 g/cm3 3 surface seawatersurface seawater

Salinity greatest influence on density in Salinity greatest influence on density in polar oceanspolar oceans Polar ocean is isothermalPolar ocean is isothermal

Our ocean is Our ocean is layered layered due to density due to density

differences at depthdifferences at depth PycnoclinePycnocline, abrupt change of density , abrupt change of density

with depthwith depth ThermoclineThermocline, abrupt change of , abrupt change of

temperature with depthtemperature with depth HaloclineHalocline, abrupt change of salinity , abrupt change of salinity

with depthwith depth High latitude oceansHigh latitude oceans

IsothermalIsothermal IsopycnaIsopycnal l

Fig. 5.23

Lastly…sound and light of Lastly…sound and light of seawaterseawater

Due to density, the Due to density, the speed of speed of sound sound in salt water is 1500 m/secin salt water is 1500 m/sec As opposed to 340 m/sec in airAs opposed to 340 m/sec in air

The The index of refraction index of refraction of light in of light in water is 1.33, as you increase the water is 1.33, as you increase the salinity, you increase the indexsalinity, you increase the index

Residence time and steady Residence time and steady statestate

Fig. 5.16

Carbonate bufferingCarbonate buffering Keeps ocean pH about same (8.1)Keeps ocean pH about same (8.1) pH too high, carbonic acid releases H+pH too high, carbonic acid releases H+ pH too low, bicarbonate combines with pH too low, bicarbonate combines with

H+H+ Precipitation/dissolution of calcium Precipitation/dissolution of calcium

carbonate CaCOcarbonate CaCO33 buffers ocean pH buffers ocean pH Oceans can absorb COOceans can absorb CO22 from from

atmosphere without much change in pHatmosphere without much change in pH

Fig. 5.18

Carbonate bufferingCarbonate buffering

Acidity and alkalinityAcidity and alkalinity Acid releases H+ when dissolved Acid releases H+ when dissolved

in waterin water Alkaline (or base) releases OH- Alkaline (or base) releases OH- pH scale measures pH scale measures the hydrogen the hydrogen

ion concentrationion concentration Low pH value, acidLow pH value, acid High pH value, alkaline (basic)High pH value, alkaline (basic) pH 7 = neutralpH 7 = neutral

Can you drink seawater?Can you drink seawater? No, it will make your cells No, it will make your cells

plasmolyze and you will die. plasmolyze and you will die. But we now can remove salt But we now can remove salt from seawaterfrom seawater

DistillationDistillation--most common --most common processprocess

ElectrolysisElectrolysis Reverse osmosisReverse osmosis Freeze separationFreeze separation

Fig. 5.24