Transcript Chemical Properties of Seawater

Learning Objectives
 Understand water’s structure and unique properties
 Define solutions and their properties
 Determine what properties change when a solute is
added to a solvent
 Define and explain colligative properties and
interactions of a solution
 Describe seawater’s properties and chemical
composition
 Discuss the environmental issues associated with
seawater’s chemical properties.
Water’s Chemical Structure
 Chemical Structure:
1- Oxygen and Hydrogen bonds-hydrogen shares one pair of electron with oxygen.
2- Two unpaired electron pairs are unbonded
3- Electrons shared with oxygen are strongly attracted towards the oxygen atom.
(this is called electronegativity)
4- The unequal sharing of electrons create a charge difference. Hydrogen has
slight positive charge and oxygen has a slight negative charge.
5- The structure formed is a bent polar molecular structure. Also called a Dipole
molecule.
105° Angle, 2 bonded pairs and 2 unshared pairs. H2O
Lab
1- Draw a Bohr’s model for each of elements listed below:
Hydrogen, Oxygen, Sodium, Chloride, Calcium,
Magnesium, Potassium, Nitrogen, Phosphorus, Carbon
and Fluoride.
2- Using the molecular model kits build a model of water
and other chemical compounds.
Include these compounds:
Carbon dioxide
Sodium Chloride
Bicarbonate
Use the following website to help you:
http://www.stolaf.edu/depts/chemistry/mo/struc/explore.
htm
Water Properties
 Due to the hydrogen
bonds in water, water’s
freezing and boiling
points are much
higher than other
substances.
 Water has a high heat
capacity, which means
it takes a great deal of
energy to change the
state of water.
 This is an important
factor when discussing
ocean currents and
atmospheric
conditions.
Heat Capacity of Water
Discussion:
• Which heats up faster, water or land? Give an
example of this thermal interaction.
Watch the video from How Stuff Works
• http://videos.howstuffworks.com/hsw/8451-waterheat-capacity-video.htm
Properties of Solutions
 Solution- a homogenous mixture of two or more
substances in a single physical state.
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very small
evenly distributed-uniformly
will not separate no matter how long it is allowed to stand
 Solute-substance that is dissolved
Solvent-substance that does the
dissolving
Example: Salt Water- Salt-Solute,
Water-Solvent
Properties of Solutions
 Soluble- a substance that dissolves in
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another substance. Example: Salt and Water
Insoluble-a substance that does not dissolve
in another
Example: Oil and Water
Polar solutes tend to dissolve in polar
solvents. Example: Water is the universal
solvent due to its polar molecule. Salt Water.
Grease or oil do not dissolve in water
because both are nonpolar molecule.
(Insoluble)
Ionic compounds do dissolve in water
because they have charges which make them
polar compounds
Demonstration: Cooking Oil and Water
Free-StockPhotos.com
Time Warp:
Oil in Water
http://dsc.discovery.co
m/videos/time-warpoil-and-water.html
Ocean Connection
Problem: Oil Spills and Oil Waste
• Using the information on solutions and the
website below, explain why oil spills and waste are
an environmental problem for oceans.
http://www.waterencyclopedia.com/OcPo/Oil-Spills-Impact-on-the-Ocean.html
Photo from website
Temperature and Pressure
 solutions of gases in liquids are greatly affected by changes
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in temperature: Soda
As temperature increases the solubility of a gas in a liquid
decreases.
The effect of temperature changes on the solubility of
solids in liquids is very different from that of gases.
Solubility of solid solute increases, as temperature
increases.
solubility of a gas in a liquid is strongly influenced by
pressure
The solubility of a gas in a solvent is increased, when the
pressure is increased
Lab
1-Gas Simulation Lab
 Learning goal: To understand the properties and behavior of gases under
certain conditions, particularly under changing temperature, pressure and
volume.
 Use the website below to answer all questions:
http://phet.colorado.edu/simulations/sims.php?sim=Gas_Properties
2- Complete the Investigating How Temperature Affects Gas Solubility Lab
Colligative Properties and
Interactions
 Depends on the concentration of solute particles and
their chemical identity
 Includes vapor pressure reduction, boiling point
elevation, freezing point depression and osmotic
pressure.
 Colligative interactions-surface tension, viscosity,
cohesion and density
Seawater Properties
 Seawater is considered a solution
 Water dissolves salt (NaCl) an ionic
compound by breaking the bonds
of between ions .
Salinity: the total amount of dissolved
salt. Units: parts per thousands (ppt)
Example: Seawater 35 ppt. which
translates to 0.26 gallons (1kg) of
seawater contains about 1.13 ounces
(35 g) of dissolved salts
Click for Animation
coolcosmos.ipac.caltech.edu/.../tempscales.html
Physical Properties
 Seawater demonstrates colligative properties:
Salt (solute) lowers the freezing point of water
and raises the boiling the pt of water.
 The freezing and boiling point will depend on
the salinity of the seawater.
 An example of boiling point elevation can be
seen near the hydrothermal vents at the midocean ridges.
 Density- is controlled by salinity, pressure and
temperature. Greater than pure water because
of dissolved salts. Also depends on
temperature- example cooling surface water
with less salt content will increase in density
and sink.
http://coolcosmos.ipac.caltech.ed
u/cosmic_classroom/cosmic_refer
ence/tempscales.html
Colligative Interactions
 Salt added to water increases the
surface tension
 Salt added to water increases the
viscosity of water, however by a
small amount.
Surface water at the equator
is warmer, decreasing the
viscosity of seawater.
 Temperature effects both
interactions
Click to the photo to view
Teacher Tube Video
Lab:
 Students should be able to understand the differences
between water and seawater: (Lab is from “Life on an
Ocean Planet: Activity #1 Chapter 6. Teachers can
substitute a Lab of their choice)
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Complete “Water, More than just Wet, it’s unique” Lab
Start with Station 2 “Study of Cohesion”
Make sure you repeating the steps for each station with salt
water solution (prepared by teacher)
Complete all diagrams and label all information
Conclusion:
Explain the differences between salt water and pure
water?
Composition
 Trace elements are present in small
concentration-parts per billion
 Major constituents are listed in the
table and appear in seawater in
minute quantities.
 The ionic composition of open-ocean
water remains the same. A constant
proportion is maintained (Marcet
and Forchhammer).
 Give the chemical symbol, atomic
mass, atomic number and what
group they appear in on the periodic
table.
Table from An introduction to
the World’s Oceans
Sources of Salt
 Chemical weathering of rocks on the continents
 Earth’s interior- volcanic eruptions- water vapor and other
gases-outgassing
 Salinity remains constant through time
NOAA Website
Gases
 Most gases are
obtained from the
atmosphere and
distributed
through depths by
mixing processes.
 Nitrogen, Oxygen
and Carbon
Dioxide are the
most abundant
dissolved gases.
Information taken from Introduction to the World’s Oceans
Dissolved Gases
 Oxygen and Carbon Dioxide play important roles in the ocean
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for biological activities.
Concentrations of Oxygen are high on surface waters, while
Carbon Dioxide concentrations are low.
As depth increases, oxygen levels decrease and carbon dioxide
increases.
Both are influenced by the biology. Photosynthesis takes place at
the surface, as depth increases respiration increases and oxygen
decreases.
Carbon dioxide is added to deep waters, these deep waters can
hold high concentrations of CO2 due to low temperatures and
high pressure.
Carbon dioxide in seawater reacts with water to form carbonic
acid (H2CO3)
Seawater pH
 Water is amphoteric-it can act as an acid or base
 As an Acid water gives up H+ to become OH As a base water accepts an H+ to become an
H3O+
 In pure water- H3O+ and OH- ions are found at a
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concentration of 1.0 x 10-7 M- pH 7- neutral
Acidity or alkalinity of solutions are measured
using the pH scale.
Seawater is slightly alkaline with a pH between
7.5 and 8.5.
Buffering-is a substance that prevents sudden
changes in acidity or alkalinity of a solution.
Carbon dioxide acts as a buffer, controlling the
pH of seawater.
Click the pH scale to view a parcel of water as
its pH changes from acidic to alkaline
Carbon dioxide and Carbonic Acid
Chemistry
CO2 + H2O
H2CO3
HCO3 - + H+ or CO32- + 2H+
CO2 combines with the water form carbonic acid. Carbonic acid
dissociates into bicarbonate, hydrogen ion and 2 hydrogen ions.
•This helps to maintain a constant pH
•pH of seawater depends on the concentration of CO2
•Higher concentrations of CO2more acidic seawater becomes
•Warm water at the surface has a high pH 8.5
•Cold deep water is more acidic due to high concentrations of CO2
Environmental
Concern
 Oxygen-deprived zones-
- caused by sluggish circulation and
oxygen-poor waters can reduce oxygen
concentrations at intermediate depths.
- these can occur from natural
occurrences, such as cold water rising
Click for Flash Animation
from depths bringing nutrients especially
nitrogen to the surface.
Plankton and nekton growth occurs, when these organisms die, bacteria takes
over and deplete the water of oxygen.
- Currently fertilizer runoff from farms and lawns is fueling oxygen-deprived
zones.
- Climate change can also increase the occurrences of oxygen-deprived zones.
- These zones do not sustain fish and will cause ecological and economic
problems.
Environmental Concern
 Ocean Acidity- one-third of carbon dioxide released by burning fossil fuels end up in the oceans
- evidence shows the ocean’s natural ability to process carbon dioxide is being
overwhelmed
-since the industrial revolution there has been a 30% surge in acidity
-continued emission of CO2 indicate ocean chemistry will change
drastically, this hasn’t happened for million of years.
-this will threaten a variety of calcite-secreting organisms.
Image
from:
http://ww
w.atmos.u
md.edu/~
rjs/oco/
Sources
 "Chemical detectives follow nitrogen's elusive and essential trail in the
ocean: the 'isotope effect' offers a new way to track nitrogen." Oceanus,
Dec 2008 v47 i1 p33(2). Science Resource Center. Gale. 13 July 2009
<http://galenet.galegroup.com/servlet/SciRC?ste=1&docNum=A192258
578>
 "Ocean acidification: the biggest threat to our oceans?(Washington
Watch)." BioScience, Nov 2007 v57 i10 p822(1). Science Resource
Center. Gale. 13 July 2009
<http://galenet.galegroup.com/servlet/SciRC?ste=1&docNum=A171887
003>
 "Deep-ocean life where oxygen is scarce: oxygen-deprived zones are
common and might become more so with climate change. Here life
hangs on, with some unusual adaptations." American Scientist, SeptOct 2002 v90 i5 p436(9). Science Resource Center. Gale. 13 July 2009
<http://galenet.galegroup.com/servlet/SciRC?ste=1&docNum=A90570
698>
Sources
 LeMay, B. R. (2002). Chemistry "Connections to Our Changing
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World". Upper Saddle River, New Jersey: Prentice Hall.
Sverdrup, A. &. (2008). An Introduction to the World's Oceans.
New York, New York: McGraw Hill.
Lutgens, T. &. (2009). Earth Science. Upper Saddle River, New
Jersey: Prentice Hall.
NOAA. (2008, March 25). Retrieved July 13, 2009, from
Monitoring Estuaries:
http://oceanservice.noaa.gov/education/kits/estuaries/estuaries
10_monitoring.html
Maryland, U. o. (2009, March 1). Orbiting Carbon Observatory.
Retrieved July 13, 2009, from Orbiting Carbon Observatory:
http://www.atmos.umd.edu/~rjs/oco/