Abiotic Factors 2 - Chemistry
1. Chemical make-up of Seawater
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Colligative Properties - due to H-bonding, polarity
1. high heat of fusion (335 J g-1) - only NH4
is higher
2. high heat of vaporization (44 kJ mol-1 at 24oC)
3. high specific heat (4.18 J g-1 oC-1)
4. adhesion & cohesion
a. surface tension
b. capillary action
2. Seawater has many salts.
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What does this do to the characteristics of water? Why?
1. osmotic pressure raises
2. boiling point raises
3. density increases
4. electrical conductance increases
5. vapor pressure lowers
6. freezing point is depressed
3. Table 2-3: Major Components (Elements) of Seawater
4. Other ěSaltyî Facts You Ought to know
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A kilogram of average seawater contains 34.7 g of salts =
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expressed as 34.7 ppt (g kg-1, o/oo)
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Can also be measured as conductivity relative to KCl at 15oC
at 1 atm pressure.
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Ranges
1. oceanic = 32-38 ppt
2. hypersaline > 38 ppt
3. estuarine =1-32
5. Biotic Classifications based on salt tolerance
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Euryhaline or euhaline = 30-40 ppt
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Polyhaline = 18-30 ppt
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Mesohaline = 3-18
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Oligohaline = 0.5-5 ppt
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Brackish = 5-10 ppt (varies by author)
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Hypersaline = > 35 ppt
6. Salinity measurement
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density: hydrometer & pycnometer
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resistance to elect. current: conductivity meter or salinometer
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bending of light from air to saltwater: refractometer
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chemical: determination of [Cl] through titration with AgNO3
= chlorinity
AgNO3 + NaCl <-> AgCl ( ppt þ) + NaNO3
7. Oxygen in seawater
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[O2] ~ 0.9% in seawater vs. 21% in atmosphere
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Sources: atmosphere & net photosynthesis
Photosynthesis --------->
6 CO2 + 6 H2O <--> CH12O6
+ 6O2
<------------ Respiration
8. Determination of O2 in Seawater
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DO Meter
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polarographic probe, Au+ , Ag-
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O2 diffuses through a thin membrane, generating a current
between + & - proportional to [DO] in water
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O2 is used up at the surface of the probe, so it needs to be
stirred to give accurate readings
9. DO measurement => Winkler titration
1. sample taken in BOD bottle
2. dissolved oxygen in sample converted to a brown ppt.
MnSO4 + 2KOH --> K2SO4
+ Mn(OH)2
2MN(OH)2 + O2 --> 2MNO(OH)2
(precipitate)
3. sample is acidified to liberate I2
MnO(OH)2 + 2H2SO4
--> 3 H2O + MN(SO4)2
Mn(SO4)2 + 2KI --> MnSO4
+ K2SO4 + I2
4. iodine removed by titration with Na2S2O3
2 Na2S2O3
+ I2 --> Na2S4O6 + 2NaI
5. end point is reached with a starch indicator solution
becomes colorless
10. Constituents of Seawater: CO2
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most important factor in controlling pH
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Buffer!!!! = resists change in pH
CO2 + H2O <-> H2CO3
<--> H+ + HCO3-
<-> 2H+ + CO3-2
Carbonic Acid
Bicarbonate
Carbonate
CO2 + H2O+CO3-2 <->
2HCO3-
11. CO2 facts
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~99% in seawater as bicarbonate or carbonate
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during photosynthesis,
a. CO2 is removed
b. HCO3- is converted to H2CO3 then to CO2
c. H+ used
d. pH *
e. respiration reverses process
f. O2 production or CO2 removal can be used to measure photosynthesis
12. calcification
= how shells, corals and coraline algae get their raw material
Ca+2 + 2HCO3- <-> Ca(HCO3)2
bicarbonate
calcium bicarbonate
<->
CaCO3
+ H2CO3
calcium carbonate
carbonic acid
13. Nutrients shown essential for plant growth -->
CHOPKNS CaFe, Mighty
good, but
Not always
Clean.
CuMn CoZn MoBy?
14. How do we know these elements are essential?
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Constituent analysis: grind and find out of what the tissues
are made
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Growth studies: deprive and look for deficiency symptoms, stunted
growth or death.