The Chemistry of Seawater

Chapter 6

The pH of Seawater

H+

Hydrogen cation OH-

Hydroxide anion

H+ = OH- H+ < OH- H+ > OH-

Neutral Alkaline Acidic

pH Measurement

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+ + CO3

2-

Too basicToo acidic

Salinity

Units of Concentration Weight Volume Moles

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‰

Dissolved Salts

Ionic bonds

Major Constituents

Conservative ions

Nonconservative ions

Sources of Salt

Chemical weathering Riverine input Most cations Anions from Earth’s mantle

Sources of Salt

Volcanic gases

Hydrogen sulfide Sulfur dioxide Chlorine

Sources of Salt

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

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

Regulating the Salt Balance

Rivers vs. Oceans

Residence Time

RT =

Amount of ion

Rate of sup/removal

Principle of Constant Proportions

Constant composition 1819 – Alexander Marcet 1865 – Georg Forchhammer Challenger expedition

William Dittmar Chloride ion

Determining Salinity

Electrical conductivity More ions = greater

conductance

Salinometer

Salinity (‰) = 1.80655 X chlorinity (‰)