CHAPTER 5 Water and Seawater
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Transcript of CHAPTER 5 Water and Seawater
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Basic chemistry○ Atomic structure
Nucleus = protons (positive) + neutrons (neutral)
http://www.rstp.uwaterloo.ca/manual/matter/graphic/atom.jpg
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Electrons (negative charge)
http://fig.cox.miami.edu/~cmallery/150/
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Chemical bonds Attractive force that holds atoms together Three major types
○ Ionic bonds ○ Covalent bonds○ Hydrogen bonds
http://w3.dwm.ks.edu.tw/bio/activelearner/02
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http://serc.carleton.edu/images/usingdata/nasaimages
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○ Ionic bonds Atoms “exchange” electrons fill outer shell
- becomes positive ion if lose electron - becomes negative ion if gain electron - + & – ions attracted to each other
Na & Cl Na+ + Cl-
http://www.physicalgeography.net/fundamentals/images
http://www.evsc.k12.in.us/schoolzone/schools/harrison
http://www.msnucleus.org/membership/html/k-6/rc/minerals/3
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Covalent bonds Atoms “share” electrons to fill outer shell H (hydrogen) has one electron, needs 1 more O (oxygen) has 6 electrons in outer shell, needs two
electrons Therefore, oxygen and 2 hydrogens bond to form water
Covalent bonds are stronger because there is sharing of the electrons
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/notes/chpt2
http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/cpmd-vmd
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Polarity of covalent bonds○ Electrons not equally distributed in molecule○ Water is a dipolar molecule (two polar covalent
bonds) O strongly attracts electrons slightly negative H slightly positive
- Think of oxygen as being the “bully” – it’s larger so it pulls the electrons towards it’s nucleus more often
○ Allows formation of H-bonding between water molecules
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig
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H2O molecule One hydrogen H and two oxygen O
atoms bonded by sharing electrons Both H atoms on same side of O atom Dipolar covalent bondDipolar covalent bond
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Hydrogen bonding Polarity
small negative charge at O end
small positive charge at H end
Attraction between + and – ends of water molecules to each other or other ions
Happens because of the polar covalent bondFig.
5.3
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Weak bonds between +/- ends of poles causes water molecules to "stick" together – cohesion
Gives water important distinct properties H2O molecule forms H-bonds w/ up to four
other water molecules, depending on temperature
http://www.nyu.edu/pages/mathmol/modules/waterhttp://info.citruscollege.com/lc/SUBJECTS/BIOL/CovalentBondimages
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Hydrogen bonding and water Hydrogen bonds are
weaker than covalent bonds but still strong enough to result in unique properties of water Cohesion = sticks to
other water molecules Adhesion = sticks to
other types of molecules High surface tension
http://faculty.uca.edu/~benw/biol1400
http://ucsu.colorado.edu/~meiercl/photography
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Hydrogen bonding and waterH-bonds absorb red
light, reflect blue light blue color
High solubility of chemical compounds in water
Solid, liquid, gas at Earth’s surface
Unusual thermal properties
Unusual density
http://www.pacific-promotion.com.fr/Phototek
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Water molecules in three states of matter
Ice locked in place by maximum H-bonding
(break/form)Molecules vibrate but relatively fixed
Fig. 5.5
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Changes of state due to adding or subtracting heat
Heat is energy of moving molecules
calorie is amount of heat needed to raise the temperature of 1 gram of water by 1o C
Temperature is measurement of average kinetic energy
http://www.magnet.fsu.edu/education/tutorials/magnetacademy/superconductivity101/images/superconductivity-temperature.jpg
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Unusual thermal properties of H2O H2O has high boiling
point H2O has high freezing
point
Most H2O is in liquid form of water on Earth’s surface VERY important for life
http://www.magnet.fsu.edu/education/tutorials/magnetacademy/superconductivity101/images/superconductivity-temperature.jpg
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Unusual thermal properties of H2O High latent (hidden) heatslatent (hidden) heats
ofVaporization/condensationMelting/freezingEvaporation – cools ocean
surface
H-bonds holding water together require extra energy (heat) to break bonds change states without
change in temperature (a to b, c to d in figure)
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Fig. 5.6
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Water Phase Changes
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Unusual thermal properties of H2O
Water high heat capacity heat capacity (specific heat)(specific heat)Amount of heat required to raise
temperature of 1 gram of any substance 1o C
Water can take in/lose lots of heat without changing temperature – must break H-bonds
On the other hand, rocks have low heat capacity○ Rocks quickly change temperature
as they gain/lose heat
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Global thermostatic effects Moderates temperature on
Earth’s surface – water temp less variable and less extreme than air temperaturesEquatorial oceans (hot) don’t
boilPolar oceans (cold) don’t
freeze solid
http://www.goredsea.com/media/images/EN
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Global thermostatic effects Marine effectMarine effect
Oceans moderate temperature changes day/night; different seasons
Continental effectContinental effectLand areas have greater range of temperatures
day/night and during different seasons
Look at the differences between coastal Florida compared to Orlando
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Density of water Density of water
increases as temperature decreases down to 4oC
From 4oC to 0oC density of water decreases as temperature decreases
Density of ice is less than density of water http://www.grow.arizona.edu/img/water
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Density of water
Fig. 5.10
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Density of water Dissolved solids reduce
freezing point of waterAs water freezes, the
crystalline structure “pushes out” much of the dissolved solids
Creates icy “slush” and surrounding waters become saltier
Putting salt on icy roads melts ice○ Salt lowers freezing point
of water on roads allowing it to remain liquid at colder temps http://www.ibarron.net/users/robert/pics/2003/Norway/OsloFjord11.jpg
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Table 5.2
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Water = Life• Summary:
• Unique properties of water that make life possible• High heat capacity and specific heat
• Moderates climates• Keeps equatorial regions from boiling and pole regions
from freezing solid• High latent heat – when undergoing change of state, large
amount of heat is absorbed or released• Sweat evaporating from your skin draws heat from your
body, keep you cool• Ice is less dense than liquid water• Cohesion
• Water moving up xylem in plants• Surface tension – allows plankton to stay near surface of
water
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Salinity Six elements make
up 99% of dissolved solids in seawater – from erosion of land, volcanism
Total amount of solid material dissolved in water- Traditional definition
Typical salinity is 3.5% or 35o/oo o/oo or parts per thousand
(ppt) = grams of salt per kilogram of water (g/Kg )
Adding salts changes many properties of water
Fig. 5.12
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Measuring salinity EvaporationEvaporation Chemical analysis - Chemical analysis - titrationtitration
Principle of constant proportionsMajor dissolved constituents in
same proportion regardless of total salinity
Measure amount of halogens (Cl, Br, I, F) (chlorinity)
Salinity = 1.80655 * Chlorinity (ppt) Specific gravity (1.028 g/ml)Specific gravity (1.028 g/ml)
Hydrometer Electrical conductivity Electrical conductivity
Salinometer http://iodeweb5.vliz.be/oceanteacher/resources/other/AndersonBook/images/salmeter.jpg
http://static.howstuffworks.com/gif/beer-hydrometer.jpg
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Pure water vs. seawater
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Salinity variations Open ocean salinity 33 to 38
o/oo However, coastal areas
salinity varies more widelyInflux of freshwater lowers
salinity or creates brackishbrackish conditions
Greater rate of evaporation raises salinity or creates hypersalinehypersaline conditions
Salinity may vary with seasons (dry/rain)
http://farm1.static.flickr.com/58/186020843_205a03e35e.jpg?v=0
http://www.caborojopr.com/images/cabo-rojo-salt-flats-las-salinas-puerto-rico-55.jpg
Salt flats in Puerto Rico
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How to change salinity
Add/remove water Add/remove
dissolved substances
http://seagrant.mit.edu/2ifbysea/issues/images/pamet.gif
Variation of the salinity, tidal height, nitrate, and radium-224 during a complete tidal cycle at the Pamet River Estuary inlet, Cape Cod, MA.
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Processes that add/subtract water from oceans
Precipitation (rain or snow)
Runoff (river flow)
Melting icebergs Melting sea ice
Evaporation Formation of sea
ice
Salinity decreases through:
Salinity increases through:
Floating in the Dead Sea
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Processes that add/subtract water
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Hydrologic cycle describes recycling of water near Earth’s surface
Fig. 5.15
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Processes that add/subtract dissolved substances
River flow Volcanic eruptions Atmosphere Biologic
interactions
Salt spray Chemical reactions at
seawater-sea floor interface
Biologic interactions Evaporite formation Adsorption
Physical attachment to sinking clay or biological particles
Salinity increases through:
Salinity decreases through:
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Residence time Average length of time a substance remains
dissolved in seawaterIons with long residence time are in high
concentration in seawater (Na+, Cl-)Ions with short residence time are in low
concentration in seawater percipitate out (K+, Ca2+ )
Steady state condition
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Residence time and steady state
Fig. 5.16
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pH – Acidity and alkalinity Acid releases H+ when
dissolved in water (HCl, H2SO4)
Alkaline (or base) releases OH- (NaOH)
pH scale measures the hydrogen ion concentrationLow pH value, acidHigh pH value, alkaline (basic)pH 7 = neutral
http://www3.oes.edu/ms/science6/Pictures%20of%20Science%20Concepts/pH%20Scale.gif
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Figure 5.17
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Carbonate buffering
Keeps ocean pH about same (8.1, slightly alkaline)pH too high, carbonic acid releases H+pH too low, bicarbonate combines with H+
Precipitation/dissolution of calcium carbonate CaCO3 buffers ocean pH (CaCO3 Ca+ + CO3
-)CO3
- bonds with H ions created when CO2 interacts with H2O
Oceans can absorb CO2 from atmosphere without much change in pH
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Fig. 5.18
Carbonate bufferingCarbonate buffering
Too acidic removes H+
Too basic adds H+
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Surface ocean variation of salinity Surface salinity varies primarily with latitudePolar regions: salinity
lower lots of rain/snow and runoffLow temps, not a lot of
evaporation
Mid-latitudes: higher salinity
because of evaporation (dry areas)
Equator: salinity slightly lower than mid-latitudes
due to lots of rain despite high evaporation
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Deep ocean variation of salinity Surface ocean salinity is
variable○ Due to occurrences at
surface – rain, evaporation, etc
Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water)
HaloclineHalocline, rapid change of salinity with depth
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Density of seawater 1.022 to 1.030 g/cm3 surface
seawater Saltwater more dense than pure
water That is why you can float better in
saltwater Ocean layered according to
density Density seawater controlled by
temperature, salinity, and pressureMost important influence is
temperatureDensity increases with decreasing
temperature
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Density of seawater Overall, temp has greatest
effect on density However, salinity greatest
influence on density in polar oceanspolar ocean is isothermal
(same temperature as depth increases)
Currents from lower latitudes bring higher salinity water into polar areas
But polar waters are overall isothermal AND isopycnal
http://www.waterencyclopedia.com/images/wsci_03_img0394.jpg
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Density versus depth
PycnoclinePycnocline, abrupt change of density with depth
ThermoclineThermocline, abrupt change of temperature with depth
Density differences cause a layered ocean
Mixed surface water Pycnocline and thermocline Deep water
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Desalination processes Remove salt from seawater Distillation Distillation – most common process,
but energetically costly Reverse osmosis Reverse osmosis – flimsy
membranes
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Misconceptions Increases in global temperatures in the
atmosphere and the consequent warming of the oceans will only create a problem for people living along the coast.
Water exists in the ground in actual rivers or lakes that are constantly renewed.
People drink bottle water because it is better for our health; the safety of tap water is below consumption standards.
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Ocean Literacy Principles 1e - Most of Earth’s water (97%) is in the ocean. Seawater has unique properties: it is saline, its
freezing point is slightly lower than fresh water, its density is slightly higher, its electrical conductivity is much higher, and it is slightly basic. The salt in seawater comes from eroding land, volcanic emissions, reactions at the seafloor, and atmospheric deposition.
1g - The ocean is connected to major lakes, watersheds and waterways because all major watersheds on Earth drain to the ocean. Rivers and streams transport nutrients, salts, sediments and pollutants from watersheds to estuaries and to the ocean.
3a - The ocean controls weather and climate by dominating the Earth’s energy, water and carbon systems.
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Sunshine State Standards SC.6.E.7.1 Differentiate among radiation, conduction, and convection, the three mechanisms by
which heat is transferred through Earth's system. SC.6.E.7.6 Differentiate between weather and climate. SC.8.P.8.1 Explore the scientific theory of atoms (also known as atomic theory) by using models to
explain the motion of particles in solids, liquids, and gases. SC.8.P.8.4 Classify and compare substances on the basis of characteristic physical properties that
can be demonstrated or measured; for example, density, thermal or electrical conductivity, solubility, magnetic properties, melting and boiling points, and know that these properties are independent of the amount of the sample.
SC.8.P.8.6 Recognize that elements are grouped in the periodic table according to similarities of their properties.
SC.8.P.8.8 Identify basic examples of and compare and classify the properties of compounds, including acids, bases, and salts.
SC.912.E.7.9 Cite evidence that the ocean has had a significant influence on climate change by absorbing, storing, and moving heat, carbon, and water.
SC.912.P.8.4 Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom
SC.912.P.8.5 Relate properties of atoms and their position in the periodic table to the arrangement of their electrons.