1. Properties of Water

2. Water is ESSENTIAL to life.
Living organisms are composed mostly of water.
Humans – 65%
Jellyfish – 90%
Tomato – 90%
Elephant – 70%

3. Structure of the Water Molecule
H atoms are “attached” to one
side of the O atom
This results in water molecule having a
(+) charge on the side
where the H atoms are and
a (–) charge on the side where oxygen
is.
This uneven distribution of charge is called polarity.

4. Opposite electrical charges attract
Water molecules tend to attract each other
Side with H atoms (+) attracts O side (-) of a different water molecule

5. What creates the HYDROGEN BOND?
Oxygen is slightly negative
Hydrogen is slightly positive
What creates the HYDROGEN BOND?
The +/- attraction between the H (+) of one water molecule and the O (-) of the adjacent water molecule.

6. COHESION
Force that holds molecules of a single substance together is cohesion.
Cohesion is due to hydrogen bonding between water molecules.
Contributes to upward movement of water from roots to leaves in plants.

7. SURFACE TENSION
Related to cohesion because water molecules are attracted to other water molecules.
Water molecules at the surface are pulled into body of water which causes it to bead up.

8. For water to spread out, surface tension must be reduced
Because of surface tension, water holds its shape and will not spread out
For water to spread out, surface tension must be reduced
Chemicals such as surfactants can reduce the surface tension
Surface tension enables water-striders to run on water without breaking the surface

9. ADHESION
Attractive force between two particles of different substances
Water molecules and glass molecules
Capillarity is the attraction between molecules that results in rise of liquid when it is in contact with solid

10. Temperature Moderation
Water can absorb or release large amounts of energy in the form of heat with only a slight change in temperature.
known as Heat Capacity
Another result of the multiple H bonds
A large amount of heat energy is needed for movement of water molecules to increases the temperature

11. Hot summer day – water can absorb large amount of energy from sun and can cool the air without large increase in water temp.
At night –
gradual cooling water warms the air

12. High Heat of Vaporization
As liquid evaporates, surface of liquid left behind cools down
Evaporative cooling prevents organisms from overheating
Evaporation of sweat releases body heat and prevents overheating.

13. Water is Less Dense as a Solid
Which is ice and which is water? 1

14. Water is Less Dense as a Solid
Ice is less dense as a solid than as a liquid (ice floats)
Liquid water has hydrogen bonds that are constantly being broken and reformed.
Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances. 1

15. Water is Less Dense as a Solid
Ice 1

16. Mixtures
Composed of two or more elements or compounds that are physically mixed together but not chemically combined
Water can make 2 types of mixtures: solutions & suspensions
Suspension: mixtures of water and nondissolved material
Biological example: blood

17. Solution A mixture of… Solute Solvent
A substance that is put INTO the solvent to dissolve.
Solvent
Substance that does dissolves the solute
Water = Universal Solvent

18. Acids & Bases
An important aspect of a living system is the degree of acidity or alkalinity
pH scale ranges from 0 – 14
Acids – range from 0 – 6 (0 strongest)
Neutral is 7
Bases - range from 8 – 14 (14 strongest)

19. Acids, Bases and Buffers
H2O  H+ + OH_
Water dissociated into equal amounts of hydrogen ions and hydroxide ions
The pH of pure water is 7 (neutral)
Acids have more hydrogen ions than hydroxide ions
Bases have more hydroxide ions than hydrogen ions