Learning ObjectivesUnderstand water’s structure and unique

propertiesDefine solutions and their propertiesDetermine what properties change when a

solute is added to a solventDefine and explain colligative properties and

interactions of a solution Describe seawater’s properties and chemical

compositionDiscuss 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 unbonded3- 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

Lab1- 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 dioxideSodium ChlorideBicarbonate

Use the following website to help you:http://www.stolaf.edu/depts/chemistry/mo/struc/explore.htm

Water PropertiesDue 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

Properties of SolutionsSolution- a homogenous mixture of two or

more substances in a single physical state. very small evenly distributed-uniformly will not separate no matter how long it is allowed to

standSolute-substance that is dissolved

Solvent-substance that does the dissolvingExample: Salt Water- Salt-Solute, Water-Solvent

Properties of SolutionsSoluble- a substance that dissolves in

another substance. Example: Salt and Water

Insoluble-a substance that does not dissolve in another

Example: Oil and WaterPolar 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.com/videos/time-warp-oil-and-water.html

Ocean Connection

Photo from website

Temperature and Pressuresolutions of gases in liquids are greatly affected

by changes in temperature: SodaAs 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

Lab1-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 PropertiesSeawater is considered a solutionWater 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

Physical PropertiesSeawater 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 mid-ocean 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.

coolcosmos.ipac.caltech.edu/.../tempscales.html coolcosmos.ipac.caltech.edu/.../tempscales.html

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/tempscales.html

coolcosmos.ipac.caltech.edu/.../tempscales.html

Colligative InteractionsSalt added to water

increases the surface tensionSalt 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)

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?

CompositionTrace 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 SaltChemical weathering of rocks on the continents Earth’s interior- volcanic eruptions- water vapor and

other gases-outgassingSalinity remains constant through time

NOAA Website

GasesMost 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 GasesOxygen and Carbon Dioxide play important roles in

the ocean 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 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 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.

Click for Flash Animation

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://www.atmos.umd.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=A192258578>

"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=A171887003>

"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, Sept-Oct 2002 v90 i5 p436(9). Science Resource Center. Gale. 13 July 2009 <http://galenet.galegroup.com/servlet/SciRC?ste=1&docNum=A90570698>

SourcesLeMay, B. R. (2002). Chemistry "Connections to Our

Changing 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/estuaries10_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/