10/14/2011
Properties of Water
Hydrogen Bonds
Hydrogen bonds do not join atoms …
Hydrogen bonds are attractions between compounds
1
10/14/2011
WATER
Hydrogen Bonds Give Water Unique
Properties (Part I)
Heat Storage
A large input of thermal
energy is required to disrupt
the organization of liquid
water
This minimizes temperature
changes
High Heat of Vaporization
At high temperatures,
hydrogen bonds do break
Water is changed into vapor
resulting in a cooling effect
2
10/14/2011
Heat Storage & High Heat of Vaporization
• Water’s heat
storage ability
keeps temp of
coastal areas
more stable!
Properties of Water
Heat Storage & High Heat of Vaporization
• These properties
allow water to trap
lots of heat and
take it away by
evaporative
cooling, like when
you sweat!
• Ahhhhh …
3
10/14/2011
Ice Formation
•At low
temperatures,
hydrogen bonds
don’t break
•Water forms a
regular crystal
structure that
floats
Ice is less dense than water, so
ice floats!
• This is super important
because it prevents
bodies of water from
freezing solid and
killing all life on the
surface and
underneath!
4
10/14/2011
Hydrogen Bonds Give Water Unique
Properties (Part II)
Cohesion
Attraction of water molecules to
other water molecules
Example: Surface tension
Water strider
Adhesion
• Attraction of water molecules to
other polar molecules
• Example: Capillary action
Surface Tension!
Cohesion (water to water) makes the surface of water like a
“solid” film!
5
10/14/2011
Capillary Action!
Cohesion and Adhesion Allows for
Transpiration
- The movement of water up a plant
(by “capillary action”) because of
pull from evaporation through the
leaves.
Water is a Great Solvent:
Hydrophilic & Hydrophobic Substances
Hydrophilic (“water-loving”)
substances
Polar
Hydrogen bond with water
Example: sugar
Hydrophobic (“water-fearing”)
substances
Nonpolar
Repelled by water
Example: oil
6
10/14/2011
Solution
Solute + Solvent = Solution
Solute- solid particles that dissolve
Solvent- what causes dissolving
Solution- homogenous mixture made from solute
and solvent
Concentrated: when there is more solute than solvent
Diluted: when there is more solvent than solute
The pH Scale
Measures H+ concentration of
fluid
Change of 1 on scale means 10X
change in H+ concentration
Highest H+
Lowest H+
0---------------------7-------------------14
Acidic
Neutral
Basic
BUFFERS
- Buffers are substances that resist
pH changes!
7
10/14/2011
Acids & Bases
Acids
These substances cause water
to release its H+
Acidic solutions have pH < 7
Bases
These substances grab H+
from water, leaving behind
OH- ions
Basic solutions have pH > 7
8