Seawater Chemistry

Pure substances that cannot be broken down into simpler chemical entities by ordinary chemical reactions. Elements Periodic Table 112 known elements

Major Elements Comprising the Biological Molecules of Living Things C arbonC arbon H ydrogenH ydrogen O xygenO xygen N itrogenN itrogen P hosphorusP hosphorus S ulfurS ulfur

Other Major Elements of Living Things Calcium (Ca)Calcium (Ca) Potassium (K)Potassium (K) Chlorine (Cl)Chlorine (Cl) Magnesium (Mg)Magnesium (Mg)

Atomic structure Atoms are the building blocks of all matter Nucleus contains: –Neutrons (no charge) – Protons (+ charge) Outer shell(s) contain: –Electrons (– charge)

proton neutron electron hydrogen atom helium atom carbon atom Electron Shell Configurations of Atoms 1p, 0n, 1e-2p, 2n, 2e- 6p, 6n, 6e-

atomic number: number of p; #p = #e- 2 He  2e- and 2p He

atomic mass (atomic wt.) : sum of masses of p+n He  2p + 2n, atomic mass = He He p + ne-

p = n = e- = Atomic number = Atomic mass = C Carbon Atom

O16O17O18 stable isotopes Isotope Atoms that differ in the number of neutrons 16 8 O 18 8 O 17 8 O #p #p+n O

Molecule Two or more atoms held together by chemical bonds OxygenO 2 NitrogenN 2 AmmoniaNH 3 Carbon DioxideCO 2 WaterH 2 O MethaneCH 4 GlucoseC 6 H 12 O 6

Ion An atom that has either gained or lost electrons such that it exhibits a net charge Na + Cl -

Sodium (Na) Atom 11 P + 12 N o

Sodium (Na + ) Ion 11 P + 12 N o

Chlorine (Cl) Atom 17 P + 18 N o

Chloride (Cl - ) Ion 17 P + 18 N o

Some Examples of Ions HydrogenH + PotassiumK + Fluoride F - Calcium Ca +2 NitrateNO 3 -NitrateNO 3 - PhosphatePO 4 -3PhosphatePO 4 -3

Bond Types Bond Types : Ionic Covalent Hydrogen

Ionic Bonds Transfer of electron 17 P + 18 N o 11 P + 12 N o

Covalent Bonding: Covalent Bonding: electron sharing O H H

Between Water Molecules Covalent bond Hydrogen bond

Boiling Point: 100 o C Freezing Point: 0 o C Density: 1g/cm 3 Properties of Water gasliquid solid

The formation of ice As water cools to 4°C: –Molecules slow –Water contracts –Density increases Below 4°C: –Hydrogen bonds form –Water expands As water freezes: –Expands by 9%

IceDensity vs Temp ( o C)

Properties of Water 1.High heat capacity 2.High heat of vaporization 3.High Surface tension 4.Polarity solvent properties

Properties of Seawater Heat capacity: Heat capacity with salinity Evaporation: Evaporates more slowly than fw Specific gravity: Pure water density = g/cm 3 Seawater (2 o C) density = g/cm 3 Seawater’s Boiling Point: As salinity, the boiling point

Seawater’s Freezing Point: As salinity, the freezing point Salt is an antifreeze- doesn’t freeze until -2 o C 35 o / oo ) Pancake ice

Refractometer Salinometer

Na + - Weathering of crustal rock Cl - - from the mantle by way of volcanic vents and outgassing from mid-ocean rifts Mg ++ - mid ocean rifts

Processes affecting seawater salinity Processes that decrease seawater salinity: –Precipitation –Runoff –Icebergs melting –Sea ice melting Processes that increase seawater salinity: –Sea ice forming –Evaporation

Salt IonIons in sw ( 0 / 00 ) Cl Na SO Mg Ca K HCO Br H 3 BO Sr F Total34.38

Global surface salinity

Salinity variations Location/typeSalinity Normal open ocean33-38‰ Baltic Sea10‰ (brackish) Red Sea42‰ (hypersaline) Great Salt Lake280‰ Dead Sea330‰ Tap water0.8‰ or less Premium bottled water0.3‰

Global ocean circulation that is driven by differences in the density of the sea water which is controlled by temperature and salinity.

White sections represent warm surface currents. Purple sections represent deep cold currents

Desalination The production of drinkable water from seawater Techniques: 1.Distillation- water vapor and condensation 2.Freezing- ice crystals form leaving salt behind 3.Reverse osmosis- sw is forced through a semipermeable membrane; only water molecules pass through 4.Electrodialysis- e- charged, semipermeable membranes draw salt ions out of sw 5.Salt absorption- chemically active resins or charcoals are used to draw off the dissolved salt ions  fw

Distillation of seawater seawater evaporation freshwater Solar energy Widely used technique plastic

Reverse Osmosis

Acids HCL  H + + Cl - Proton donor, i.e., they donate H + ions HCl is a strong acid with a pH 1-2

Na + + OH -  NaOH NH 3 + H +  NH 4 OH - + H +  H 2 O HCO 3 - +H +  H 2 CO 3 Proton acceptor, i.e., they take up H+ ions NaOH is a strong base ~pH 12 Bases

Neutralization- HCl + NaOH  H 2 O + NaCl

Buffer- resists dramatic changes in pH; ex. tums, rolaids…buffers stomach acid

Acidic0-6 Neutral7 Basic (alkaline)8-14 Type of Solution pH Value 0-14

Logarithmic scale blood

Carbon Dioxide System in the Ocean Respiration Photosynthesis C 6 H 12 O 6 +6O 2 6CO 2 + 6H 2 O 6CO 2 + 6H 2 O C 6 H 12 O 6 +6O 2 Air Water CO 2 gas

CO 2 + H 2 O ↔ H 2 CO 3 ↔ HCO H + ↔ CO H + By-product of respiration carbonic acid bicarbonate carbonate The addition of CO 2 makes water acidic The effects of CO 2 in an ocean system

Bicarbonate buffer Seawater too basic: H 2 CO 3 HCO H + pH drops Seawater too acidic: HCO H + H 2 CO 3 pH rises

Ocean Acidity

Global Ocean Acidity

Consequences of Ocean Acidity Animals with CaCO 3 skeletons affected Plankton Corals Mollusks Fish o.uk/2/hi/science /nature/ stm Fisheries

In a high CO 2 world, the ocean will be… More acidic More stratified More oligotrophic, but better light conditions Less oxygenated Consequences of Ocean Acidity

Acid Rain in Marine Environment reduces ability of marine organisms to utilize calcium carbonate Coral calcification rate reduced 15-20% Skeletal density decreased, branches thinner

Inquiry 1.How many neutrons in 7 N? 2.Why do all the oceans have relatively the same proportion of salinity? 3.At what temperature is fw most dense? 4.Of the following pH’s which is most acidic? Why are there no plants at the compensation depth? 6. Why can a water strider walk on water? 7. Besides temperature and salinity, what physical factor effects thermohaline circulation? 8. What is the oceans most dense sea water called? 14