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Seawater Chemistry

Seawater Chemistry. Elements. Pure substances that cannot be broken down into simpler chemical entities by ordinary chemical reactions. Periodic Table 112 known elements. Major Elements Comprising the Biological Molecules of Living Things. C arbon H ydrogen O xygen N itrogen P hosphorus

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Seawater Chemistry

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  1. Seawater Chemistry

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

  3. Major Elements Comprising the Biological Molecules of Living Things • Carbon • Hydrogen • Oxygen • Nitrogen • Phosphorus • Sulfur

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

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

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

  7. atomic number: number ofp; #p = #e- 2He2e- and 2p He

  8. He atomic mass (atomic wt.): sum of masses ofp+n He 2p + 2n, atomic mass = 4 4 2He p + n e-

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

  10. O Isotope Atoms that differ in the number of neutrons 16 8 O 17 8 O 18 8 O #p+n #p O16 O17 O18 stable isotopes

  11. Molecule Two or more atoms held together by chemical bonds Oxygen O2 Nitrogen N2 Ammonia NH3 Carbon Dioxide CO2 Water H2O Methane CH4 Glucose C6H12O6

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

  13. Sodium (Na) Atom 11 P+ 12 No

  14. 11 P+ 12 No Sodium (Na+) Ion

  15. 17 P+ 18 No Chlorine (Cl) Atom

  16. 17 P+ 18 No Chloride (Cl-) Ion

  17. Some Examples of Ions • Hydrogen H+ • Potassium K+ • Fluoride F- • Calcium Ca+2 • Nitrate NO3- • Phosphate PO4-3

  18. Bond Types: • Ionic • Covalent • Hydrogen

  19. 11 P+ 12 No Ionic Bonds Transfer of electron 17 P+ 18 No

  20. O Covalent Bonding:electron sharing H H

  21. Between Water Molecules Hydrogen Bonds Hydrogen bond Covalent bond

  22. Properties of Water Boiling Point: 100oC Freezing Point: 0oC Density: 1g/cm3 solid gas liquid

  23. 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%

  24. Ice Density vs Temp (oC)

  25. Properties of Water • High heat capacity • High heat of vaporization • High Surface tension • Polarity solvent properties

  26. Properties of Seawater Heat capacity: • Heat capacity with salinity Evaporation: • Evaporates more slowly than fw Specific gravity: • Pure water density = 1.000 g/cm3 • Seawater (2 oC) density = 1.028 g/cm3 Seawater’s Boiling Point: • As salinity , the boiling point

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

  28. Determining Salinity Salinometer Refractometer

  29. Source of Ocean Salts: • Na+ - Weathering of crustal rock • Cl- - from the mantle by way of volcanic vents and outgassing from mid-ocean rifts • Mg ++ - mid ocean rifts

  30. 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

  31. Major Solutes in Seawater Salt Ion Ions in sw (0/00) Cl- 18.980 Na+ 10.556 SO42- 2.649 Mg2+ 1.272 Ca2+ 0.400 K+ 0.380 HCO3- 0.140 Br- 0.065 H3BO3 0.026 Sr2+ 0.013 F- 0.001 Total 34.38

  32. Global surface salinity

  33. Salinity variations

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

  35. Thermohaline Circulation White sections represent warm surface currents. Purple sections represent deep cold currents

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

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

  38. Reverse Osmosis

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

  40. Bases Proton acceptor, i.e., they take up H+ ions NaOH is a strong base ~pH 12 Na+ + OH- NaOH NH3 + H+ NH4 OH -+ H+ H2O HCO3- +H+ H2CO3

  41. Neutralization- HCl + NaOH H2O + NaCl

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

  43. pH Scale 0-14 Type of Solution pH Value Acidic 0-6 Neutral 7 Basic (alkaline) 8-14

  44. pH Scale Logarithmic scale blood

  45. Carbon Dioxide System in the Ocean CO2 gas Air Water Photosynthesis 6CO2 + 6H2OC6H12O6 +6O2 Respiration C6H12O6 +6O2 6CO2 + 6H2O

  46. The effects of CO2 in an ocean system By-product of respiration CO2 + H2O ↔ H2CO3↔ HCO3- + H +↔ CO32- + 2H+ carbonic acid bicarbonate carbonate The addition of CO2 makes water acidic

  47. Bicarbonate buffer Seawater too basic: H2CO3 HCO3- + H +pH drops Seawater too acidic: HCO3- + H + H2CO3pH rises

  48. Ocean Acidity

  49. Global Ocean Acidity

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