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ChemicalOceanography

Dr. David K. RyanDepartment of ChemistryUniversity of Massachusetts Lowell&Intercampus of Marine Sciences Program

http://faculty.uml.edu/David_Ryan/84.653

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Water –Amazing Stuff

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Chemical OceanographyPhysical Chemistry ofSeawater (E&H Chap. 3)

Seawater is 96.5 % H2O Water unique substance & solvent Review structure Discuss selected unusual properties Consequences of water anomalies Phase diagrams

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Hydrogen Bonding is key to anomalous properties of water

H-Bonding results from polarity

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Dipole &QuadrapoleDiagrams(Millero 2006)p. 125

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Arrangement for Hydrogen Bonding - Pentamer

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Water Clusters Dynamically Form, Break and Re-formFrank & WenFlickering Cluster Model

(Millero 2006)

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Millero

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Water Properties

High Heat Capacity (Cp)

(Heat energy to raise 1 g of water 1 oC)

Prevents extreme ranges of temperature (temp buffering)

Allows heat transfer by water masses to be large

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Water Properties

High Heat of Fusion(∆H = 79 cal/g)

(Heat energy for melting solid)

Absorption or release of latent heat results in high thermostatic effecta.k.a. Enthalpy of Fusion (kJ/kg)

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Water Properties

High Heat of Vaporization(∆H = 540 cal/g)

(Heat energy for evaporating liquid)

Highest of all liquidsResults in evaporative cooling and transfer of

heat to atmosphere, thermostatinga.k.a. Enthalpy of Vaporization

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Large Quantities of Heat are Absorbed & Released During Phase Changes

(Wiley 1999)

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Water Properties

Thermal Expansion

(temperature of maximum density)

Waters with low or no salt content have maximum density above freezing points

Ice floats

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Simple PhaseDiagram ofWater

(Wiley 1999)

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Water Properties

High Dielectric Constant

(highest of almost all substances)

Results in charge insulating powerImportant in dissolution of saltsImportant in hydration of ions

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Water Properties

Relatively High Viscosity

(high for low molecular weight substance)

Important in wave and current formation

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Water Properties

High Surface Tension

(highest of all substances)

Controls drop formation, important in waves and many surface properties

Important in cell physiology

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Interfacial Tensioncreates appearanceof a “skin” on surface

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Water Properties

High Heat Conduction

(highest of all liquids)

Important for small scale heat transfer as in cells

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Water Properties

High Transparency

(absorption of radiant energy high in IR and UV)

Water is colorlessImportant in photosynthetic and photochemical

processes

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Water Properties

Low Electrolytic Dissociation

(neutral molecule containing some OH- and H+)

Autodissociation of water important in acid-base chemistry, many geological and biological processes

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Water Properties

Low Compressibility

(similar to solids)

Little change in density as pressure increases with depth

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Simple PhaseDiagram ofWater

(Wiley 1999)

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Detailed Phase Diagram of Water Showing Forms of Ice

(Atkins 1990)

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Structure of Ice 1h with water pentamer highlighted (Emerson & Hedges Fig 3.4, page 67)

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Structure of Ice 1h, Hexagonal with Space Giving Low Density(Pilson 1998)

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Comparison ofIce and Liquid WaterStructures (NYU-SVL)

Ice 1h Liquid Water

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Water Clusters Dynamically Form, Break and Re-form

(Millero 2006)

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Structure or Association of WaterMolecules Versus Temperature and Affect on Density (Libes 1992)

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“Water, water, every where,Nor any drop to drink.”

The Rime of the Ancient Mariner

Samuel Taylor ColeridgeCirca 1798

What happens whenwe add solutes to water?

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Solutes (ParticularlyIons) are StructureBreakers

More accurately they form new structuresReorient some water moleculesCause new associationsModify propertiesAlter much of the Physical Chem. (Physicochemical Properties)

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TemperatureDensityDiagram forPure Water& SeawaterSalinity of 35

(Pilson 1998)

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SomePropertiesUndergoDramaticChanges

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Adding an Ion Like Sodium (Na+)Changes SomeThings inH2O

Polarity, HighDielectricConstantResult inStrongSolvation orHydration ofNa+ by H2O

PrimarySolvationShell of H2O

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SecondarySolvationShell or aSecondSphere ofH2O isBound tothe First

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Normal H2O Structure ExistsOut Here for “Bulk” Water

Bulk Water Bulk Water

DisruptedWater StructureExists inHere

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(Emerson & HedgesFig 3.6, page 69)

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Hydrated Ion(Morel 1993)

= H2O

= cation

Primarysolvent

Secondarysolvent

Disorderedsolvent

BulkSolution

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For Anions theConcept is AnalogousOnly ReversedWith Respect tothe Orientationof the H2O

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Other Effects Also Occur

Long Range(Non-Specific)Repulsion

Long Range(Non-Specific)Attraction

δ–

OrientedOutward

δ+ OrientedOutward