The Chemistry of Seawater

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The Chemistry of Seawater

• Chapter 6

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The pH of Seawater

• H
• Hydrogen cation
• OH-
• Hydroxide anion

H OH-
H lt OH-
H gt OH-
Neutral
Alkaline
Acidic
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pH Measurement
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Buffering Capacity of CO2

• Buffer
• Substance that prevents sudden, or large, changes
  in acidity or alkalinity of a solution
• CO2 H2O ?? H2CO3 ?? H HCO3-?? 2H CO32-

Too acidic
Too basic
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Salinity

• Units of Concentration
• Weight
• Volume
• Moles

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Ocean Salinity

• Measured in grams of salt per kilogram of
  seawater
• 1kg of seawater is made up of 965 g of water and
  35 g of salt
• 35

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Dissolved Salts

• Ionic bonds

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Major Constituents
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• Conservative ions
• Nonconservative ions

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Sources of Salt

• Chemical weathering
• Riverine input
• Most cations
• Anions from Earths mantle

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Sources of Salt

• Volcanic gases
• Hydrogen sulfide
• Sulfur dioxide
• Chlorine

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Sources of Salt

• Hydrothermal vents
• Discovered in 1977
• Geyser on the seafloor
• Spews super-hot, mineral-rich water
• Very biodiverse

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Sources of Salt

• Hydrothermal vents
• Black Smokers
• Hottest of the vents
• Spew iron and sulfide, which combine to form iron
  monosulfide
• White Smokers
• Cooler temp
• Barium, Calcium and Silicon

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Regulating the Salt Balance
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Rivers vs. Oceans
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Residence Time

• RT
• Amount of ion
• Rate of sup/removal

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Principle of Constant Proportions

• Constant composition
• 1819 Alexander Marcet
• 1865 Georg Forchhammer
• Challenger expedition
• William Dittmar
• Chloride ion

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Determining Salinity

• Electrical conductivity
• More ions greater conductance
• Salinometer
• Salinity () 1.80655 X chlorinity ()