1. NOTES: 2.2 – Properties of Water

2. Water Overview…
• Water is perhaps the most important compound in living organisms
• Because so many substances can dissolve in water:
molecules and ions are free to
move and collide with one
another in the reactions of life;
water serves as a means of
material transportation
(i.e. blood, plant sap)

3. Water Overview… Living cells are 70%-95% water
Water covers approx. ¾ of earth.
In nature, water naturally exists in all 3 states of matter: solid, liquid and gas

5. Water is a POLAR molecule
• the bonds that hold the hydrogen and oxygen atoms together are POLAR COVALENT BONDS…
so, a water molecule has a positive end and a
negative end

6. Water is POLAR…
• POLAR WATER MOLECULES attract one another, as well as ions and other polar molecules

7. Water Molecules…
• The polarity of water molecules
results in HYDROGEN BONDING
• a HYDROGEN BOND is the
attraction of opposite charges
between hydrogen and oxygen
• How many hydrogen bonds can a single water molecule make with neighboring water molecules?

9. Properties of Water (as a result of polarity and H-bonding):
► COHESION: molecules are held together by H bonds
• contributes to upward
movement of water in
plants from roots to leaves

10. Tension– Cohesion Model

11. Properties of Water
► ADHESION: water sticks to other surfaces (by polarity or H bonds)…
…can counteract gravity in plant vessels

12. ► SURFACE TENSION: measure of how difficult it is to stretch the surface of a liquid
-water has greater surface tension than most liquids because at the air/water interface the surface water molecules are H-bonded to each other and to the water molecules below
-causes water to “bead”
-creates a “skin” on the surface

14. ► HIGH SPECIFIC HEAT (resists changes in temp)
• Specific Heat: amt. of heat that must be absorbed or lost for 1 gram of a substance to change its temp by 1°C
• Water’s high specific heat means that it resists temp. changes when it absorbs or releases heat
*Heat is absorbed to break H-bonds; and given off when they form

17. Compounds that are HYDROPHILIC (“water loving”), are soluble in water:
ionic compounds: charged regions of polar water molecules have an electrical attraction to charged ions
polar compounds: charged regions of polar water molecules are attracted to oppositely charged regions of other polar molecules

18. Compounds that are HYDROPHOBIC (“water fearing”) and are insoluble in water:
Nonpolar compounds: symmetric distribution in charge, or composed of nonpolar bonds

19. ► EVAPORATIVE COOLING: after high temp
► EVAPORATIVE COOLING: after high temp. molecules have evaporated, the remaining liquid is cooler (ex: sweating)
-stabilizes temp. in aquatic ecosystems
-protects organisms from overheating
*(as 1 g of water evaporates
from our skin, 539 g
of body cools by 1°C)

20. The air in the shower stall is at the same temperature as the air outside, but there's less water vapor outside to condense on the skin.

21. HEAT OF VAPORIZATION (WHILE CHANGING STATE)
EVAPORATIVE COOLING
HEAT OF VAPORIZATION (WHILE CHANGING STATE)
SPECIFIC HEAT
(WHILE WATER IS HEATING)

22. ► WATER EXPANDS WHEN IT FREEZES
• because of H-bonding, water is less dense as a solid than it is as a liquid...ice floats!
• since ice is less dense, it forms on the surface at first
• as water freezes, it releases heat to the water below and insulates it!
• Oceans and lakes don’t freeze solid!!

24. ► WATER IS THE SOLVENT OF LIFE
cell
► WATER IS THE SOLVENT OF LIFE
• due to its polarity, water is a versatile solvent

25. Water forms Solutions
All the components of a solution are evenly distributed throughout the solution.
In a saltwater solution, table salt is the solute—the substance that is dissolved.
Water is the solvent—the substance in which the solute dissolves.

26. Acids, Bases, and pH
Water molecules sometimes split apart to form hydrogen ions and hydroxide ions.
This reaction can be summarized by a chemical equation in which double arrows are used to show that the reaction can occur in either direction.

27. pH Scale
Chemists devised a measurement system called the pH scale to indicate the concentration of H+ ions in solution.
The pH scale ranges from 0 to 14.
At a pH of 7, the concentration of H+ ions and OH– ions is equal. Pure water has a pH of 7.
Acids have a pH less than 7.
Bases have a pH greater than 7.