Water
Describe Water
(46NBtop)
How would you describe water to someone
who had never seen it before?
• You might say that pure water has no color, no
taste, and no odor. You might even say that
water is a rather plain, ordinary substance.
• If you asked a chemist to describe water, the
chemist would say that water is very unusual. Its
properties differ from those of most other familiar
substances.
NB Setup:
– NB44 - Hydrosphere Unit Page
• (label & decorate)
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NB45 - Hydrosphere Objectives & Tracker
NB46 – Describe Water /
NB47 - Unique Properties of Water Webquest
NB48 - Unique Properties of Water Foldable
NB49 – Properties of Water Station Lab
NB50 – Frayer Diagrams Cohesion/Adhesion
Why is water so Important?
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All life on Earth depends on water
Our fresh water resources are scarce
Global warming is effecting the hydrosphere
Different types of pollution are contaminating all
of our water
• Etc, etc, etc….
• Now…. Let’s look at what makes water so special
in the first place….
Properties of Water
foldable Instructions
•
Fold your white paper into a 3-fold
brochure
Title is “Unique Properties of Water”
Label inside 3 section:
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1. Universal Solvent/Solubility
2. Cohesion/Adhesion (Capillary Action!!)
3. Surface Tension
•
Label two outside sections:
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Polarity/Specific Heat
Density/Buoyancy
foldable Instructions
What goes in our foldable?
 Facts!
 Definitions!
 Pictures!
 Be creative! Own it!
 What seems important TO YOU??
Polarity of Water
• In a water molecule two
hydrogen atoms form
single polar covalent
bonds with an oxygen
atom.
– A water molecule is a
polar molecule with
opposite ends of the
molecule with
opposite charges.
Water has a variety of unusual
properties because of attractions
between these polar molecules.
– Each water molecule
can form hydrogen
bonds with up to
FOUR neighbors.
– Gives water more
structure than other
liquids… and therefore
causes lots of
interesting things to
happen……
foldable Instructions
What goes in our foldable for Polarity?
 Facts!
 Definitions!
 Pictures!
 Be creative! Own it!
 What seems important TO YOU??
Capillary Action
Now, how does that
work??
Hydrogen bonds hold water together, a
phenomenon called ….
Cohesion &
Adhesion
Cohesion
Co-hesion=
1. “Co-” = share
2. “-hesion”= bonded
example -> (adhere)
So…
Cohesion refers to waters
attraction to other water
molecules.
Adhesion
– Adhesion refers to
attraction to other
substances.
• Water is adhesive to
any substance with
which it can form
hydrogen bonds.
Trees have specialized structures to transport water:
- xylem and phloem “plumbing”
* Water molecules are “dragged” from the roots to the
top of the tree by capillary action and cohesion!
Capillary action
water evaporates from
leaves = transpiration
adhesion,
cohesion and
capillary action
water taken up by
roots
Surface Tension
• Have you ever watched water striders (spiders!!!)
skate across the surface of a pond without sinking?
• They are supported by the surface tension of the
water….
• Surface tension is the tightness across the
surface of water that is caused by the polar
molecules pulling on one another.
(its related to cohesion)
Some animals can stand,
walk, or run on water
without breaking the
surface.
– Water has a greater surface tension than most other
liquids because hydrogen bonds among surface
water molecules resist stretching or breaking the
surface.
– Water behaves as if
covered by an invisible
film.
Where else have you seen surface tension
in action?
Specific Heat
• It is a steamy summer day. The air is hot, the
sidewalk is hot, and the sandy beach is hot. But
when you jump into the ocean, the water is
surprisingly cool! If you go for an evening swim,
however, the water is warmer than the cool air.
Because….
• Water has a HIGH Specific Heat.
• Specific Heat is the amount of heat
that must be absorbed or lost for
one gram of a substance to change
its temperature by 1oC.
Three-fourths of the earth is covered by
water. The water serves as a large heat
sink responsible for:
1. Prevention of temperature The Earth is over 75% water!
fluctuations that are outside
the range suitable for life.
2. Coastal areas having a mild
climate
3. A stable marine environment
Universal Solvent
“Universal” Solvent
• What happens when you make a fruit drink
from a powdered mix?
• homogeneous = solution.
• In an aqueous solution, water is the
solvent.
Shhh….Water is not really a universal
solvent, but it is very versatile because of
the polarity of water molecules.
Solvent for Life
• Can be either:
– Solute (if its not main
ingredient)
– Solvent (= Aqueous solution )
• Hydrophilic (H20 loving)
– Ionic compounds dissolve in
water
– Polar molecules (generally)
are water soluble
• Hydrophobic (H20 phobic)
Nonpolar compounds
Cohesion and solubility allow….
• Water to transport molecules dissolved in it:
– Blood, a water-based solution, transports molecules of
nutrients and wastes organisms
– Nutrients dissolved in water get transported through
plants
– Unicellular organisms that live in water absorb
needed dissolved substances
Density of Water
• Most dense at 4oC
• Contracts until 4oC
• Expands from 4oC to
0oC
The density of water:
1. Prevents water from freezing from the bottom up.
2. Ice forms on the surface first—the freezing of the
water releases heat to the water below creating
insulation.
3. Makes transition between season less abrupt.
Solid water (ice) is less dense than
liquid
• Ice is less dense than water: the molecules are spread
out to their maximum distance
Density = mass/volume
same mass
but a larger
volume
How does ice float?
• Ice is “Buoyant”
– It floats on top of the more dense liquid
water…
– But what is “Buoyancy”?
Oceans and lakes don’t freeze solid
because ice floats
 water expands as it
solidifies
 water reaches
maximum density at
4-degrees C
 water freezes from
the top down
 organisms can still
live in the water
underneath the ice
during winter
Water is Transparent
• The fact that water is clear allows light to
pass through it
– Aquatic plants can receive sunlight
– Light can pass through the eyeball to
receptor cells in the back
Let’s Wrap it up!
• Ticket out the door:
– 3/2/1: 3 things you learned, 2 questions, 1 favorite or
Least favorite thing about today’s lesson
• H.W. - Brochure
– Follow given rubric, and use notes from today
– Due Mon/Tues
Warm-Up - 46NBbottom
What properties of water do you feel make it a
Unique/Special Substance? Explain and
justify your response.
Frayer Diagrams
Stations on Water Properties
Let’s Wrap it up!
• Ticket out the door ~ Take #2
– 3/2/1: 3 things you learned, 2 questions, 1 favorite or
Least favorite thing about today’s lesson
– Psst! (did your questions from last lesson get
answered? Let me know!!)
• H.W. – Frayer Diagrams completed
• Also:
– Complete all station reports, if not completed in
Class.
– Notebooks due Friday for NB check!