Water Unit
SOL 6.5
The student will investigate and understand the unique properties and characteristics of water and
its roles in the natural and human-made environment. Key concepts include
a) water as the universal solvent; b) the properties of water in all three states; c) the action of water in physical and chemical
weathering; d) the ability of large bodies of water to store heat
and moderate climate; e) the origin and occurrence of water on Earth; f) the importance of water for agriculture, power
generation, and public health; and
g) the importance of protecting and maintaining water resources.
Web Sites:
http://www.unesco.org/water/
http://www.wateryear2003.org/en/ev.php-URL_ID=1462&URL_DO=DO_TOPIC&URL_SECTION=201.html
Youtube clips
http://www.youtube.com/watch?v=KiZJOTt3Dl0&feature=fvw
http://www.youtube.com/watch?v=KiZJOTt3Dl0&feature=fvw
http://www.youtube.com/watch?v=VGoJuLX3BQQ&NR=1&feature=fvwp
http://www.youtube.com/watch?v=DVCYlST6mYQ&safety_mode=true&persist_safety_mode=1&safe=active 10 minute video on properties of water……NICE
Water can be found in most areas of the Earth.
Water is found naturally as
a Liquid
http://static.guim.co.uk/Guardian/society/gallery/2007/jul/11/childrensservices/GD3984317@Wat
er-Babies---pics-s-550.jpg
http://www.depts.ttu.edu/CASNR/Water/water1.jpg
Solid
Gas
Water: the Universal Solvent
Water is Unique!
Why?
1. Only compound that
commonly exist in
all 3 forms in nature
(solid,liquid,gas)
2. Universal solvent
(many, many
materials dissolve in
H2O
3. Polar molecule (1
side slightly positive,
1 side slightly
negative) (leading to
cohesion, adhesion,
capillary action)
4. High surface tension
This daisy is under the
water level, which has risen gently and smoothly. Surface tension
prevents the water from submerging the flower.
5. Large range of
temps (0-100C)
liquid form WOW! The following link is good.
http://www.nyu.edu/pages/mathmol/textbook/info_wa
ter.html This is a fine link for studying water.
http://www.youtube.com/watch?v=Jy65YrPYZb0
Water, the great mystery. One of a number of
segments.
WATER
FORMULA for WATER
DIAGRAM of a WATER MOLECULE
POLAR MOLECULE
ADHESION
COHESION
MISCIBILITY
SOLVENT
SOLUTE
SOLUBLE/SOLUBILITY/SOLUTION
SURFACE TENSION
MENISCUS
Reservoir Volume 103 km3
%total Residence
Time
Ocean 1,370,0
00
97.25 > 3000
years
Glaciers &
Ice caps
29,000 2.05 10 - 100
thousand
years
groundwater 9500 0.68 Highly
variable, 10 -
300
Lakes 125 0.01 several
years
Soils 0.005 .005 1- 2 years
Atmospher
e
13 0.001 10 days
*but high
flux!
Rivers 1.7 0.0001 2 - 3
weeks
Biosphere 0.60 0.0000
4
weeks -
years
Total 1,408,7
00
100
Water that exists on, at or within the
Earth’s surface layer is termed the
hydrosphere.
Random Fact: Water weighs 8.37
pounds per gallon at 4 degrees C.
H2O The Mickey Mouse Molecule
Water is a polar molecule which gives each molecule the appearance of “Mickey Mouse ears”.
Atomic Structure of Water
2 hydrogen atoms bonded to 1 oxygen atom causes unique electrochemical properties.
Hydrogen side has slight positive charge. Other side has negative charge.
Hydrogen atoms form 105O angle
All atoms aspire to completely fill their orbitals. When the orbitals are full, there are no valence electrons available to participate in chemical bonds. So these atoms get left alone! That is why we call helium, neon, argon, krypton, and xenon INERT. They have full orbitals, so they have no way to interact with other elements.
Hydrogen would like to have 1 more electron to fill up its' orbital. Oxygen would love to have 2 more to fill up its' 2nd orbital. SO HYDROGEN AND OXYGEN SHARE ELECTRONS, which makes both of them happy. This is called a covalent bond.
Covalent bond: the sharing of electrons between atoms.
THE HYDROGEN BOND IS WHAT GIVES WATER IT’S HEAT CAPACITY, IT’S DENSITY BEHAVIOR, AND DISSOLVING ABILITY.
www.geo.umn.edu/
Properties Key to Life Handouts.doc
(honors)
Properties Key to Life Handouts Academic.doc (academic)
Temperature (degrees
Celsius) Density (grams per cubic
centimeter)
0 (solid) 0.9150
0 (liquid) 0.9999
2 1.0000
20 0.9982
40 0.9922
60 0.9832
80 0.9718
100 (gas) 0.0006
Freezing Point = Melting Point
Using the Pressure Cooker at High Altitudes
At High Altitude (3500-6500 ft) cooks really have
to plan ahead to do some of the same things the
rest of us take fro granted. The reason foods have
high altitude instructions is because the boiling point
of water changes with altitude. As you go higher, the
boiling temperature decreases. At sea level, the
boiling point of water is 212° F (100° C). As a
general rule, the boiling point temperature
decreases by 1 degree F for every 540 feet of
altitude (0.56° C for every 165 meters). On top of
the14,000 foot Pike's Peak, for example, the boiling
point of water is 187° F (86° C).
Figuring Altitude in Pressure Cooking
In order to cook at elevations above 2000 feet,
the cooking times in a standard pressure cooker
must be altered according to a very specific formula:
For every 1000 ft above 2000 ft
elevation, increase the cooking time by 5%.
Using a little basic physics we know that water
boils at 212°F at sea level, but as altitude increases
the temperature at which water boils decreases at
the rate of 1.9°F for each 1,000 feet because there
is less atmospheric pressure on the surface of
liquids. By adding 5PSI, water boils at about 16°F
higher than it naturally would at that altitude; at
10PSI it boils at 28 °F higher, and at 15PSI, water
boils 38°F higher. Therefore, by increasing the
pressure, as in a pressure cooker, the temperature
Boiling Point Of Water*
Altitude
in
Feet
Altit
ude in
Meters
Deg
rees F.
Deg
rees C.
0 0 212.
0
100.
0
500 152 211.
0
99.4
1000 305 210.
0
98.9
2000 610 208.
2
97.9
3000 914 206.
2
96.8
4000 121
9
204.
4
95.8
5000 152
4
202.
6
94.8
6000 182
9
200.
7
93.7
7000 213
4
198.
7
92.6
8000 243
8
196.
9
91.6
10,00
0
304
8
194.
0
90.0
12,50
0
381
0
189.
8
87.7
14,00 426 187. 86.3
at which water boils is raised and the food is cooked
more quickly.
A standard pressure cooker operating at 15 PSI,
rises the boiling point of water to 250°F (121°C) at
sea level. At 240°F (which corresponds to only 10.5
PSI) the cooking times must be increased by 33% in
comparison to the standard 15PSI.
0 7 3
* = These temperatures will all vary
according to whatever your current
barometric pressure is. The ONLY way
to find the exact boiling point is to take
standard barometric pressure (29.92
millibars) and subtract the local
barometric pressure (found on a
barometer or in the local weather
forecast). Multiply the resulting number
by 1.8518. Add 212 to that and you will
find the current boiling point of water
wherever you happen to be at the time
of testing (altitude does not matter). If
you use this formula to find the boiling
point, the result will only be correct for
a short while because the barometric
pressure is always changing. You'll
need to get an updated local
barometric pressure and refigure the
formula.
Surface Tension
The following illustration shows how water molecules are attracted to each other to create high surface tension. This property can cause water to exist as an extensive thin film over solid surfaces. In the example above, the film is two layers of water molecules thick.
Solution, Solvent, Solute
The larger amount is the SOLVENT. The lesser amount is the SOLUTE. A SOLUTION is a mixture of one substance (SOLUTE) dissolved (evenly distributed) in another, larger substance (SOLVENT) http://www.chemistryland.com/CHM107/Water/WaterTutorial.htm
The motto
regarding
solubility is "Like Dissolves Like." For example, to clean off
grease, use something that is greasy like vegetable oil or
butter. I had one student say he noticed potato chips
cleaned his hands. It must have been the oil in the chips.
http://www.chemistryland.com/CHM107/Water/WaterTutorial.htm
This child has a
clean face now, but
after eating the cotton
candy, it won't be. To
clean off cotton candy
we know that water
would good for that, not
oil. Remembering "Like Dissolves Like" we guess that water
and sugar must be alike in some way.
Here is a 3-d model of the sugar, glucose. I've placed water molecules at strategic places around the sugar molecule. Do you notice that the positive side of water is attracted to
the negative oxygen atoms? The negative side of water is attracted to the positive hydrogens which are bonded to the oxygens (not the other hydrogens bonded to carbons). Because water pulls the charged areas, it will pull the sugar into the water and hold it there. That's why water is good at cleaning the face of someone eating cotton candy or other sweets.
Water is known as the
Universal Solvent
Water is a good solvent due to
its polarity. Substances that will
mix well and dissolve in water
(e.g. salts) are known as
"hydrophilic" (water-loving)
substances, while those that do
not mix well with water (e.g. fats
and oils), are known as
"hydrophobic" (water-fearing)
substances.
LIKE MOLECULES DISSOLVE LIKE
Polar dissolve polar
COHESION
A property of water
and some other
substances in which
the molecules are
attracted to molecules
of the same substance.
Water molecules, being
polar, act like LITTLE
MAGNETS—they are
attracted to poles of
opposite charges.
ADHESION
When water molecules are attracted to molecules of a different substance.
http://www.nano-
world.org/frictionmodule/content/0200makroreibung/0600adhesionmodel/bild1.gif
CAPILLARY ACTION
Water molecules love some other molecules and
hate other molecules.
When water molecules stick to
other molecules that are also little
magnets, it is called "molecular
adhesion." This explains why it is
easy to clean up spilled water with
a paper towel: the water
molecule's little magnets like to stick to the cellulose molecules of
the paper, which are also like little magnets. Water molecules will
stick to any other molecules that
are like little magnets (polar), but do not like to get involved with
any molecules that hate little
magnets (nonpolar), like oil. Oil and water don't mix, right? That is
why you have to shake the salad dressing real hard before you pour
it: the oil molecules hate the water little magnets.
Paper towels are made out of
trees,
http://www.sciencebuddies.org/science-fair-projects/project_ideas/PlantBio_img014.jpg
and trees are made out of cellulose. The leaves make
molecules of sugar out of sunlight, water, and carbon dioxide, then
combine the sugars into huge
sugar chains. These sugar chain molecules are called cellulose. This
name comes from the fact that the plant material is made of cells, and
the "-ose" word ending means
"sugar". Cellulose is also a
great magnet (polar molecule), so water sticks to
cellulose just like a magnet to the refrigerator door!
Now that we know a bit
about water molecules, let's
look at how water acts in a little tube.
The redwood tree's trunk is made up of millions of
little bitty tubes (xylem), and these tubes are made of cellulose. The
water molecules like to stick together and like to stick to the walls of the
tubes of cellulose, so they rise up the tubes by capillary action.
The water pressure decreases as it rises up the tree. This is because the capillary action is
fighting the weight of the water. Although the xylem tube is very thin, and therefore the weight of
the water is very low, it is not zero. Eventually, the effects of gravity on the water starts to
equal the effects of capillary action. http://www.davidlnelson.md/Cazadero/Trees&CapillaryAction.htm
Drawing pig blood into a pipette=capillary action
http://oslovet.veths.no/teaching/pig/pigbleed/2.jpg
http://www.mobot.org/gardeninghelp/images/factsheets/2b.jpg
REVIEW http://www.ccs.k12.in.us/
chsBS/kons/kons/physical_properties_of_water.html
http://ga.water.usgs.gov/edu/waterproperties.html
http://kentsimmons.uwinnipeg.ca/cm1504/water.htm
Because water absorbs strongly in the infrared portion of the light spectrum, a small amount of visible red light is absorbed as well, resulting in water's slightly blue color when seen in mass quantities such as a lake or ocean.
UNIQUE PROPERTIES OF WATER?
1.
2.
3.
4.
5.
6.