1. Properties of Water!
Why Water is Special

2. Why do we study water properties in biology class?
About 2/3 of the mass of a cell is water!
Most life-sustaining reactions occur in water solutions

3. Polarity
Polarity describes the distribution of electrons in a molecule
Polar molecules have an uneven distribution of electrons.
Example: Water + -

4. Water forms Hydrogen Bonds
Hydrogen Bonds: Form due to attraction between water molecules.
Not as strong as ionic/covalent bonds
Water can form up to 4
hydrogen bonds at once

5. Properties of water
Emergent Properties of water contribute to Earth’s fitness for life
Cohesion/Adhesion
Surface tension
Specific Heat
Solution pH

6. Water is Cohesive
Cohesion: Water molecules are drawn tightly together (on the surface of a lake or a pond, this forms a film, which is called surface tension)
Explains why:
Water beads on a surface (like the lab table)
Insects can walk on water

7. A Cool Example of Cohesion / Surface Tension: Water Strider Insect
Water Strider - Video
YouTube:
Surface Tension
YouTube:
Jesus Lizard

8. Water is Adhesive =
Adhesion = Water adheres (sticks) to different surfaces
Ex: Measuring water in a graduated cylinder
Water adheres (sticks) to the glass more than it adheres to itself.
Why is this property of water important to organisms?
Allows water to move through bloodstream.

9. Cohesion Adhesion Ex: Water Bubble Ex: Water on a Leaf
Surface Tension and Adhesion

10. Water can undergo Capillary Action
Capillary Action= Water can flow up a tube, against gravity
Ex: Plants absorbing water through their roots (Transpiration)

11. Specific Heat
Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC
Water has a high specific heat which allows it to minimize temperature fluctuations to within limits that permit life
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form

12. Moderation of temperature
Water’s high specific heat
Change temp less when absorbs/loses heat
Large bodies of water absorb and store more heat  warmer coastal areas
Create stable marine/land environment
Humans ~65% H2O  stable temp, resist temp. change

13. High Heat of Vaporization
Amount of energy to convert 1g or a substance from a liquid to a gas
In order for water to evaporate, hydrogen bonds must be broken.
As water evaporates, it removes a lot of heat with it.
Sweating cools the body as heat energy from the body changes sweat into a gas 1

14. Moderation of temperature
Evaporative Cooling
Water has high heat of vaporization
Molecules with greatest KE leave as gas
Stable temp in lakes & ponds
Cool plants
Human sweat

15. Water has a High Heat Capacity
Water absorbs a lot of heat from the air without having a large temperature change
So…lakes and oceans often stabilize air temperatures
Water absorbs heat when it evaporates; this is why sweating helps us cool down!

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

17. Water is Less Dense as a Solid
Ice 1

18. States of Matter
Liquid
Gas
Solid

20. Water is less dense in its solid form
Water is less dense in its solid form than it is in its liquid form (Ice floats!)
Why might it be a bad thing for ice to sink in a pond?

21. Moderation of temperature
Insulation by ice – less dense, floating ice insulates liquid H2O below
Life exists under frozen surface (ponds, lakes, oceans)
Ice = solid habitat (polar bears)

22. So why does it take so much heat to increase the temperature of water?!
You have to break the hydrogen bonds between water molecules first!

23. Solutions and Mixtures
A mixture is a substance that is made of two or more elements physically mixed together
Example: Mixing Skittles and M&Ms together
A solution is a type of mixture where one substance is dissolved in another.
Solute- the substance that is dissolved
Solvent- the substance that does the dissolving

24. Water as a solvent
Water is often referred to as the “Versatile Solvent” because of it’s ability to dissolve such a wide variety of substances.
GO WATER!!!

25. Solution The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them

26. Solvent of life Hydrophilic Hydrophobic “like dissolves like”
Affinity for H2O
Repel H2O
Polar, ions
Nonpolar
Cellulose, sugar, salt
Oils, lipids
Blood
Cell membrane

27. Water Has a Neutral pH
pH: measure of how acidic or basic a solution is
scale is 0 to 14
If pH = 7, then substance is neutral (not acid or base)