Formation and Nature of the Hydrosphere

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Formation and Nature of the Hydrosphere
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Intermolecular Forces

• There are three intermolecular forces that when
  combined, determine the state of a molecular
  substance at a given temperature and pressure
• London Dispersion Force (LDF)
• Dipole-Dipole Force (DDF)
• Hydrogen Bonding (H-bond)

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London Dispersion Force

• Force of attraction between temporary,
  fluctuating dipoles on adjacent molecules of all
  substances
• As sizes of molecules increase, the ability of
  adjacent molecules to distort each others
  electron symmetry increases since valence
  electrons are less tightly held by the nuclei

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London Dispersion Forces

• One instantaneous dipole can induce another
  instantaneous dipole in an adjacent molecule (or
  atom).
• The forces between instantaneous dipoles are
  called London dispersion forces.

exist between all molecules
Prentice Hall 2003, Chp 11
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London Dispersion Forces (LDF)
LDF increases with increasing size of similar
molecules. Assume size ? molecular weight.
Higher M.W. increased LDF higher BP
Prentice Hall 2003, Chp 11
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Dipole-Dipole Force (DDF)
Force of attraction between permanent dipoles on
adjacent polar molecules
Most readily observed in properties of molecules
having same size (molecular wt.)
http//wine1.sb.fsu.edu/chm1045/notes/Forces/inter
mol/Forces02.htm
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Dipole-Dipole Forces
Dipole moment is a measure of polarity, as dipole
moment increases, polarity increases.
Increased Polarity higher BP
Prentice Hall 2003, Chp 11
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Hydrogen Bonding

• Polar molecules containing H bonded to either F,
  O, or N exhibit LDF, DDF, and an additional
  intermolecular force called H-bonding
• H-bonding is the force of attraction between a
  partially positive H in one polar molecule and a
  lone pair of electrons on O, N, or F in an
  adjacent molecule

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Hydrogen Bonding
Each water molecule can form H-bonds (shown as
dotted lines) with 4 other water molecules. All
H-O-H bond angles are 109.5º
http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/H/HydrogenBonds.html
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Evidence for H-Bonding
As size decreases, LDF decreases, and B.P.
decreases. However, the smallest molecule, water,
has the highest B.P. due to a strong additional
force H-bonding
Ebbing/Gammon, General Chemistry,6th,Houghton
Mifflin, 1999, 461
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Evidence for H-Bonding
HF and NH3 also exhibit H-bonding while CH4 does
not
Ebbing/Gammon, General Chemistry,6th,Houghton
Mifflin, 1999, 461
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Intermolecular Forces and the Formation of Oceans

• Of the molecules in the second atmosphere of
  primitive Earth, water was most abundant and had
  the strongest intermolecular forces (LDF, DDF,
  and H-bonding)
• As Earth cooled, water was the first to liquefy
  and it came down as rain which formed the
  hydrosphere - oceans, etc

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Bonding, Intermolecular Forces and Primitive Earth
LDF London Dispersion Force DDF
Dipole-Dipole Force
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How Oceans Became Salty

• Once water liquefied, solar heating evaporated
  water into the atmosphere where it cooled and
  fell again as rain - called Water or Hydrological
  Cycle
• The falling rain dissolved some gases and then
  percolated through soil dissolving some solids
  which it deposited in the oceans

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Water Cycle (omit living matter and transpiration)
www.italocorotondo.it/.../ hydrological_cycle.htm
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Solid Solutes and Polarities of Best Solvents
General rule Like dissolves like - maximum
solubility occurs when solute and solvent are of
same type or nearly the same type
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Dissolving an Ionic Substance

• Salt is held together by strong electrostatic
  forces, the attraction between oppositely charged
  ions
• When placed in water there is a strong force of
  attraction between ions and dipoles of water
  molecules
• Whichever force is stronger determines whether
  the substance is soluble

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Dissolving of NaCl in Water
Ion-dipole force ion-ion force making NaCl
somewhat soluble in water allowing it to
accumulate in oceans
http//www.iun.edu/cpanhd/C101webnotes/chemical2
0reactions/ioniccmpdsol.html
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Composition of Sea Water

• If a liter of ocean water is evaporated, the
  following solids separate in the order and
  amounts given 0.12 g CaCO3, 1.55 g CaSO4, 29.7 g
  NaCl, 2.48 g MgSO4, 3.32 g MgCl2, 0.55 g NaBr,
  and 0.53 g KCl
• These solubilities can also be expressed as
  molarity (moles/liter)

Baird/Goffke, Chemistry in Your Life,Freeman,NY,
2003, 412
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Concentrations of Solutions

• Molarity (M) - the number of moles of the solute
  per liter of solution
• M moles of solute/liters of solution
• Find molarity of a solution containing 2 moles of
  HCl in 4 liters of solution
• M moles of solute/liters of solution
• M 2 moles/4 L 0.50 moles/L HCl

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In 100 mL of sea water there is 0.332 g of
MgCl2. Find the molarity of seawater with respect
to MgCl2.
Mole of MgCl2 1(24.3) 2(35.5) 95.3 g.
Moles of MgCl2 0.332 g/95.3 g/mole 0.0035
moles. M 0.0035 moles/0.100 L 0.035 M
MgCl2
http//misterguch.brinkster.net/molaritytutorial.h
tml
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Reactions of Aqueous Solutions

• Water percolating through soils in different
  regions of the earth dissolved different
  substances
• When solutions having different compositions came
  together in oceans, they sometimes reacted with
  each other
• Two common reactions in aqueous solutions are
  precipitation and acid/base

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Precipitation Reaction
Reaction involving the formation of an insoluble
substance which separates from the solution
Silberberg, Chemistry, Mosby, MO, 1996, 146
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Acids/Base Reactions Bronsted-Lowry Definitions

• Acid is a proton (H) donor
• Base is a proton (H) acceptor
• Reaction of acid with base is transfer of the
  proton (H) from the acid to the base
• NH3(aq) HCl(aq) NH4Cl(aq)
• NH3 is Bronsted base, HCl is Bronsted acid

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Reactions on Primitive Earth

• Water reacted with metal oxides to produce bases
  CaO H2O Ca(OH)2, and with non-metal oxides
  to produce acids CO2 H2O H2CO3
• A later acid/base and precipitation reaction
  produced water and precipitated limestone
  Ca(OH)2(aq) H2CO3(aq) CaCO3(s) 2 H2O(l)

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Physics of Ocean Waves
For d 4000 m, V (9.8 m/s24000 m )1/2 or 200
m/s or 450 miles/hr
http//www.tulane.edu/sanelson/geol204/tsunami.ht
m
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Comparison of Wind Waves and Tsunamis
Wind-generated waves usually have period (time
between two successive waves) of five to twenty
seconds and a wavelength of 100 to 200 meters
Tsunami can have a period in the range of ten
minutes to two hours and  wavelengths greater
than 500 km.
http//www.ess.washington.edu/tsunami/images/tsulg
.jpg, http//www.tulane.edu/sanelson/geol204/tsun
ami.htm
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Tsunami

• A tsunami is a series of waves generated by an
  undersea disturbance such as an earthquake
• From the area of the disturbance, the waves will
  travel outward in all directions
• Time between wave crests may be from 5 to 90
  minutes, and wave speed in open ocean will
  average 450 miles per hour

http//www.fema.gov/hazards/tsunamis/tsunami.shtm
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http//news.bbc.co.uk/1/hi/in_depth/4136289.stm
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http//news.bbc.co.uk/1/hi/in_depth/4136289.stm
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How Earthquakes Under the Ocean Produce Tsunamis
Seafloor is uplifted and down-dropped, pushing
the entire water column up and down. The
potential energy that results from pushing water
above mean sea level is then transferred to
horizontal propagation of the tsunami wave
(kinetic energy).
http//science.howstuffworks.com/tsunami2.htm,
http//walrus.wr.usgs.gov/tsunami/basics.html
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http//news.bbc.co.uk/1/hi/in_depth/4136289.stm
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Landfall of a Tsunami
As the depth of the water decreases, the velocity
of the tsunami decreases, wavelength decreases
and wave height increases
Tsunamis can travel up to 600 mph at the deepest
point of the water, but slow as they near the
shore, eventually hitting the shore at 30 to 40
mph. The energy of the wave's speed is
transferred to height and sheer force as it nears
shore.
http//www.nationalgeographic.com/ngkids/9610/kwav
e/how.html
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Mega Tsunami
http//wwp.mega-tsunami.com/
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Destruction Caused by a Tsunami
http//news.bbc.co.uk/1/hi/in_depth/4136289.stm
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Theory of Continental Drift - Wegener 1915
Pangaea "all the land" - one continent that split
to form all the present day continents
http//www.agen.ufl.edu/chyn/age2062/lect/lect_28
/lect_28.htm