1. Water— The Elixir of Life!

2. Why are we studying water?
All life occurs in water
inside & outside the cell

3. Water’s 4 main properties

4. Chemistry of water Water is polar molecule
remember polar covalent bonds
+ & – poles

5. H2O molecules form H bonds with each other
Water
1st property of water – COHESION/ADHESION occurs due to hydrogen bonding
H2O molecules form H bonds with each other
+ attracted to –
creates a sticky (cohesive) molecule

6. Water
Cohesion
H bonding between H2O creates cohesion (binding of like molecules)
Remember drops of water on a penny?
surface tension
water is “sticky”

7. 1st Property of Water (cont’d)- Adhesion
H2O molecules form H bonds with other substances (adhesion-attraction between different kinds of molecules)
Capillary action
Ex: Water “climbs up” fiber (paper towel)

8. How does H2O get to top of tree?
Water
How does H2O get to top of tree?
Example of Capillary Action - Transpiration

9. 2nd Property of Water – Versatility as a solvent
H2O is a good solvent due to its polarity
Polar H2O molecules surround + & – ions
Solvents dissolve solutes creating aqueous solutions
In your words
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

10. Hydrophilic Hydrophilic – water loving
Some substances have affinity for H2O
Look at diagram- polar or non-polar?
Ionic
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?

11. Hydrophobic Hydrophobic – water hating
Some substances do not have affinity for H2O
polar or non-polar?
non-ionic
What dissolves in water easily?
polar or non-polar molecules?
How about Oxygen? Does that dissolve in H2O?
fat (triglycerol)

12. 3rd Property of Water – Expansion upon freezing
Most substances are more dense when they are solid.
But not water…water expands
Therefore, water is less dense as a solid than as a liquid which is why ice floats in water!

13. Below, hydrogen bonds form a crystal with a loose structure
Water
Ice floats in water
Below, hydrogen bonds form a crystal with a loose structure

14. Floating ice is the key to life.
Water
Floating ice is the key to life.
Oceans & lakes don’t freeze solid
if ice sank… ?
surface ice insulates water below
seasonal turnover of lakes
cycling nutrients

15. Water
4th property of water – Regulates temperature due to its high specific heat. The heat of vaporization is higher than most liquids making it resistant to change
Due to H bonding, H2O resists changes in temperature
takes a lot to heat it up
takes a lot to cool it down
H2O moderates temperatures on Earth

16. 4th property usefulness: Evaporative cooling
Water
4th property usefulness: Evaporative cooling
Organisms rely on heat of vaporization to remove heat and help resist a change in temperature.
From a biological perspective, why is temperature stability important?
Think warm blooded

17. Summary Water is a polar molecule
The special properties of water, often due to its hydrogen bonding, make life on Earth possible
The chemical behavior of water governs how organisms function

18. Questions
1. A person with swollen gums rinses his mouth with warm salt water, and the swelling decreases. Which has
occurred?
A The swollen gums have absorbed the saltwater solution.
B The saltwater solution lowers the temperature of the water in the gums.
C The salt in the solution has moved against the concentration gradient.
D The water in the gums has moved from a high to a low concentration of water.

19. Question 2
Water is an essential part of all life and considered the universal solvent. Which of the
following properties is responsible for this?
A. Water forms polar bonds that attract other similar molecules.
B. Water forms ionic bonds that attract other similar molecules.
C. Water is found in all organic molecules.
D. Water forms four covalent bonds.

20. Question 3
Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability to sweat to lower body temperature?
A. Water’s change in density when it condenses
B. Water’s ability to dissolve molecules in the air
C. The absorption of heat by the breaking of hydrogen bonds.
D. Water’s high surface tension forms four covalent bonds.