Honors Biology
WATER
AND
pH Notes
August 22nd, 2014
Pick up: Water and pH Notes
 Immediately Take out a grading pen
and put your 3.4 and 3.5 summaries on
your desk
 Warm up: Watch the short video and
on your warm up sheet, please list all
the properties of water that show up!
 Agenda: Exam Check, Start Water
notes, Water Activity?

Characteristics of Water
http://www.allaboutwater.org/waterfacts.html Cool water facts.
 A single water molecule is held together
by polar covalent bonds, BUT, if you
want to attach a bunch of water
molecules together, (Which is normally
what we think of when we hear the
word water), we need Hydrogen Bonds.

Molecule Image

Dotted lines are the
Hydrogen Bonds
Key Properties of Water
(table 3.2)
A) Heat storage
 B) Ice Formation
 C) High Heat of Vaporization
 D) Cohesion/adhesion
 E) Hydrophobic/hydrophilic

A) Heat Storage
When talking about temperature, we are really talking
about how fast molecules are moving. IF they move fast
the temperature is high, if they move slowly, the
temperature is low.
 Large input of thermal energy is required to disrupt the
organization of liquid water
 This minimizes temperature changes
 Water heats up and cools down VERY slowly because
you first need to break the hydrogen bonds.

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Biological importance of heat
storage
Your body doesn’t immediately boil
when you step outside in July.
 You can swim in your swimming pools
in October and not freeze, but you can’t
jump in your pool during June before
the pool heats up enough.
 What other things can you think of?

B) Ice Formation

Low temperature means the H-Bonds
are pretty stable, but they may take on
a cool property. They arrange
themselves in a way that makes ice
LESS dense as a solid. Most other
liquids react the opposite when they get
colder.
Biological Importance of Ice
Formation
Ice floats!
 Oceans/bodies of water freeze from the
top down. Creates a nice insulated
layer so that life can still exist in the
ocean.
 Any other reasons you can think of?


C) High heat of vaporization
To Vaporize means to turn into a gas.
What does it take for liquid water to do
this?
 Move fast enough so that the H-bonds
can break. When the H-Bond is broken,
it carries with it a great deal of heat!

Biological importance …..

Sweating cools you
off! When you
sweat, the fast
moving water is
literally leaving your
body… the
molecules left
behind are moving
slowly so you feel
cooler.
D) Cohesion/Adhesion

Because of the H-Bonds, water can
stick to other water molecules and to
other objects. (Examples: Capillary
Action and Surface Tension)
Biological Importance of
Cohesion/Adhesion
http://www.youtube.com/watch?v=CT4
pURpXkbY
 Towels can actually dry you off when
you get out of the shower.
 Straws work
 Any other ideas?

Surface tension

Molecules inside a
water droplet are
attracted in all
directions. Drops on
the surface are
attracted to the
sides and inward.
E) Hydrophobic and
Hydrophilic
The term Hydrophobic means “water
fearing”.
 The term Hydrophilic means “water loving”.
 The terms really mean the ability or inability
to DISSOLVE in water. Like dissolves like.
 Since water is polar, any polar molecule can
dissolve in water.

Biologic Importance
Most of our blood is made up of water,
so nutrients can be dissolved in our
blood and transported through out the
body without needing to be big and
clunky and blocking up the veins and
arteries.
 Our skin must be hydrophobic since we
don’t dissolve when it rains.

Structure of Water video

http://www.youtube.com/watch?v=KiZJ
OTt3Dl0&feature=related
pH
Reminder: Water is held together by
___________________ bonds.
 These are relatively __________ bonds.
 These bonds are constantly _________
and _____________.
 When water breaks apart, there is a
way to represent this using chemical
equations. (Dissociation of water)

Dissociation of water
IF you measure how
much is H+ you would
find the concentration
to be 1/10,000,000.
 Use exponents
 10 to the negative 7
 [ ] brackets mean
“concentration” so
[H+] is translated to
concentration of
Hydrogen

What is a logarithm?
How many of one number do we
multiply to get another number?
Example of a logarithm

Example: How many 2s do we multiply
to get 8?

Answer: 2 × 2 × 2 = 8, so we needed
to multiply 3 of the 2s to get 8

So the logarithm is 3
What are we trying to determine
by using the pH scale?
We want to know how much of a
solution is made out of Hyrdogen Ions.
(By number and by weight.)
 In a liter of pure water, 1 in 550 million
water molecules is ionized at any point
in time. Why not more?
 1/10,000,000 of the weight (Molar
mass)
 What does ionization mean?

IONization
Ionization= When one of the hydrogen
molecules in a water molecule is
“ripped’ away from the water molecule,
two Ions are formed. H+ (Hydrogen
Ions) and OH- (Hydroxide molecule)
 Why does this happen? Spontaneous
Ion formation. (Covalent bonds in
water sometimes break spontaneously)

[H+] and pH values are
opposite!
A) if pH is low, what about the [H+] ?
 B) if the pH is high, what about the
[H+]?

Acids vs Bases
Acids: Anything that dissolves in water
and adds H+. OH NO! IMBALANCE!
 Bases: Anything that dissolves in water
and combines with H+. Not necessarily
bad, but now there is an imbalance with
the OH- ion.
 THEY NEED TO STAY BALANCED!

BUFFERS
What would a buffer do if pH falls?
 What would a buffer do if pH rises?
