Seawater Chemistry

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Pure substances that cannot be broken down into simpler chemical entities by ordinary chemical reactions.

Pure substances that cannot be broken down into simpler chemical entities by ordinary chemical reactions.

ElementsElements

Periodic Table 112 known elements

An element is composed of atoms (0.1-1 nm in diameter)

Atom cluster of small particles (proton, neutron, electron)

Protons (p +)

Neutrons (n o)

Electrons (e -)

proton

neutron

electron

hydrogenatom

heliumatom

carbonatom

1p, 0n, 1e- 2p, 2n, 2e- 6p, 6n, 6e-

atomic number: number of p; #p = #e-

2He2e- and 2p

He

atomic mass (atomic wt.): sum of masses of p+nHe 2p + 2n, atomic mass = 4

4

2He

He

p + n e-

p = n = e- = Atomic number = Atomic mass =

C

Carbon Atom

O16 O17 O18

stable isotopes

IsotopeIsotopeatoms that differ in the number of neutrons

16

8 O

18

8 O17

8 O#p

#p+n

O

Major Elements Comprising the Biological Molecules of

Living Things

Major Elements Comprising the Biological Molecules of

Living Things

• CCarbonarbon• HHydrogenydrogen• OOxygenxygen• NNitrogenitrogen• PPhosphorushosphorus• SSulfurulfur

Other Major Elements of Living Things

Other Major Elements of Living Things

• Calcium (Ca)Calcium (Ca)• Potassium (K)Potassium (K)• Chlorine (Cl)Chlorine (Cl)• Magnesium (Mg)Magnesium (Mg)

Some Important Trace Elements of Living Things

Some Important Trace Elements of Living Things

• Boron (B)Boron (B)• Cobalt (Co)Cobalt (Co)• Iron (Fe)Iron (Fe)• Copper (Cu)Copper (Cu)• Fluorine (F)Fluorine (F)• Zinc (Zn)Zinc (Zn)

MoleculeTwo or more atoms held

together by chemical bondsOxygenOxygen OO2 2

NitrogenNitrogen NN22

AmmoniaAmmonia NHNH33

Carbon DioxideCarbon Dioxide COCO22

WaterWater HH22OO

MethaneMethane CHCH44

GlucoseGlucose CC66HH1212OO66

• Carbohydrates: C6H12O6 (glucose)

• Lipids: C3H8O3 (glycerol) + 3C16H32O2 (fatty acids)

• Proteins: COOH-NH2

• Nucleic Acids: sugar, PO4, N2 containing base

Organic Molecules

CompoundBinding two or more different kinds of elements together

NaClNaCl

CHCH44

CC66HH1212OO66

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 No

Sodium (Na+) Ion

11 P+

12 No

Chlorine (Cl) Atom

17 P+

18 No

Chloride (Cl-) Ion

17 P+

18 No

• Hydrogen H+

• Potassium K+

• Fluoride F-

• Calcium Ca+2

• Magnesium Mg+2

• HydroxideHydroxide OHOH--

• BicarbonateBicarbonate HCOHCO33--

• NitrateNitrate NONO33--

• PhosphatePhosphate POPO44-3-3

• Ionic• Covalent• Hydrogen

Transfer of electron

17 P+

18 No

11 P+

12 No

electron sharing

O

HH

Between Water Molecules

Covalent bond

Hydrogen bond

Boiling Point: 100oCFreezing Point: 0oCDensity: 1g/cm3

Properties of WaterProperties of Water

gas liquid 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%

Ice Density vs Temp (oC)

Properties of WaterProperties of Water

1.High heat capacity

2.High heat of vaporization

3.High Surface tension

4.Polarity solvent properties

The ocean moderates coastal temperatures

• Water has high heat capacity, so it can absorb (or release) large quantities of heat without changing temperature

• Moderates coastal temperatures

The ocean moderates coastal temperatures

Hawaii Average High and Low Temperature

Hawaii Average Ocean Water Temperature

Interconnections of water molecules

• Polarity causes water molecules to form weak (hydrogen) bonds between water molecules

• Water sticks to itself and to other substances

• Allows water to be the universal solvent

Water as a solvent

• Water dissolves table salt (NaCl) by attracting oppositely charged particles

• Pulls particles out of NaCl structure to dissolve it

Water has a high surface tension

Water in the 3 states of matter• Latent (hidden) heat = energy that is either

absorbed or released as water changes state

Properties of SeawaterProperties 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

When NaCl dissolves, each ion becomes hydrated

Seawater’s Freezing Point:

• As salinity , the freezing point

• Salt is an antifreeze- doesn’t freeze until -2oC (@35 o/oo)

Lattice structure of an ice crystal

Sea ice (pancake ice)

Salt Ion Ions in sw (0/00)Cl- 18.980Na+ 10.556SO4

2- 2.649Mg2+ 1.272Ca2+ 0.400K+ 0.380HCO3- 0.140Br- 0.065H3BO3 0.026Sr2+ 0.013F- 0.001 Total 34.38

• Na+ - Weathering of crustal rock

• Cl- - from the mantle by way of volcanic vents and outgassing from mid-ocean rifts

• Mg ++ - mid ocean rifts

                                           

                                                                                                             

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

Acids

HCL H+ + Cl-

Proton donor, i.e., they donate H+ ions

HCl is a strong acid with a pH 1-2

Bases

Na+ + OH- NaOHNH3 + H+ NH4

OH - + H+ H2O

HCO3 +H+ H2CO3

Proton acceptor, i.e., they take up H+ ions

NaOH is a strong base ~pH 12

NeutralizationHCl + NaOH H2O + NaCl

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

AcidsAcids

HCL H+ + Cl-

Proton donor, i.e., they donate H+ ions

HCl is a strong acid with a pH 1-2

BasesBases

Na+ + OH- NaOHNH3 + H+ NH4

OH - + H+ H2O

HCO3- +H+ H2CO3

Proton acceptor, i.e., they take up H+ ions

NaOH is a strong base ~pH 12

Neutralization- HCl + NaOH H2O + NaCl

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

Neutralization & BuffersNeutralization & Buffers

pH ScalepH Scale

Acidic 0-6Neutral 7Basic (alkaline) 8-14

Type of Solution pH Value

0-14

pH ScalepH ScaleLogarithmic scale

Dep

th (

m)

Concentration of dissolved gas (ppm)

0

500

1000

1500

2000O2

CO2

90 94 98 102 106 110

1.5 3.0 4.5 6.0 7.5

CO2O2

O2 and CO2 vs ocean depth

Compensation depth

Carbon Dioxide System in the OceanCarbon Dioxide System in the Ocean

Respiration

Photosynthesis

C6H12O6 +6O2 6CO2 + 6H2O

6CO2 + 6H2O C6H12O6 +6O2

Air

Water

CO2 gas

CO2 + H2O ↔ H2CO3 ↔ HCO3- + H + ↔ CO3

2- + 2H+

By-product of respiration

carbonic acidbicarbonate

carbonate

The addition of CO2 makes water acidic

The effects of pH in an ocean systemThe effects of pH in an ocean system

Carbonate bufferCarbonate buffer

Seawater too basic:

H2CO3 HCO3- + H + pH drops

Seawater too acidic:

HCO3- + H + H2CO3 pH rises

Ocean Acidity

Global Ocean Acidity

Consequences of Ocean Acidity

Animals with CaCO3 skeletons affected• Plankton• Corals• Mollusks • Fish

http://news.bbc.co.uk/2/hi/science/nature/7933589.stm

Fisheries

In a high CO2 world, the ocean will be…

• More acidic• More stratified• More oligotrophic, but better light conditions • Less oxygenated

Consequences of Ocean Acidity

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? 3 7 6 25. 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?

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