1. Water

2. Water
A water molecule (H2O), is made up of three atoms --- one oxygen and two hydrogen. H O 1

3. Properties of Water Polar molecule Cohesion and adhesion
High specific heat
Density – greatest at 4oC
Universal solvent of life

4. Polarity of Water
In a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Gives water more structure than other liquids
Because oxygen is more electronegative, the region around oxygen has a partial negative charge.
The region near the two hydrogen atoms has a partial positive charge.
A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.
In each water molecule, the oxygen atom attracts more than its "fair share" of electrons
The oxygen end “acts” negative
The hydrogen end “acts” positive
Causes the water to be POLAR
However, Water is neutral (equal number of e- and p+) --- Zero Net Charge
2 corners are orbitals with unshared electrons and a weak negative charge
2 are occupied by hydrogen atoms that have polar covalent bonds

5. HYDROGEN BONDS Cohesive behavior Resists changes in temperature
Extraordinary Properties that are a result of hydrogen bonds.
Cohesive behavior
Resists changes in temperature
High heat of vaporization
Expands when it freezes
Versatile solvent
Hold water molecules together
Each water molecule can form a maximum of 4 hydrogen bonds
They form, break, and reform with great frequency

6. Organisms Depend on Cohesion
Hydrogen bonds hold the substance together, a phenomenon called cohesion
Attraction between particles of the same substance ( why water is attracted to itself)
Results in Surface tension (a measure of the strength of water’s surface)
Produces a surface film on water that allows insects to walk on the surface of water

7. Adhesion Attraction between two different substances.
Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton.
Capillary action-water molecules will “tow” each other along when in a thin glass tube. Which gives water the ability to “climb” structures
Example: transpiration process which plants and trees remove water from the soil, and paper towels soak up water.
Fig. 3.3
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. Moderates Temperatures on Earth
Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air.
Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.
Celsius Scale at Sea Level
100oC
Water boils
37oC
Human body temperature
23oC
Room temperature
0oC
Water freezes
What is kinetic energy?
Heat?
Temperature?
What is specific heat?

9. Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1oC.
Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for:
Prevention of temperature fluctuations that are outside the range suitable for life.
Coastal areas having a mild climate
A stable marine environment

10. Evaporative Cooling
The cooling of a surface occurs when the liquid evaporates (Under Armor)
This is responsible for:
Moderating earth’s climate
Stabilizes temperature in aquatic ecosystems
Preventing organisms from overheating

11. Density of Water Most dense at 4oC Contracts until 4oC
Expands from 4oC to 0oC
The density of water:
Prevents water from freezing from the bottom up.
Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation.
Makes transition between season less abrupt.

12. Ice is about 10% less dense than water at 4oC.
When water reaches 0oC, water becomes locked into a crystalline lattice with each molecule bonded to to the maximum of four partners.
As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state.
Ice is about 10% less dense than water at 4oC.
Fig. 3.5
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

13. Water is Less Dense as a Solid
Ice 1

14. Buoyancy
Buoyancy is the ability of a fluid to exert an upward force on an object floating in it.
Buoyant force (upward) must be greater than gravitational force (downward) in order for an object to float
Objects with a lower density than water will float in water.
Metal is more dense than water, so the shape of a boat helps it float.

15. Buoyancy and the Titanic

16. Solvent for Life Solution Hydrophilic Hydrophobic Solute Solvent
Ionic compounds dissolve in water
Polar molecules (generally) are water soluble
Hydrophobic
Nonpolar compounds

17. Solutions & Suspensions
Water is usually part of a mixture.
There are two types of mixtures:
Solutions
Suspensions

18. Solution Ionic compounds disperse as ions in water Evenly distributed
SOLUTE
Substance that is being dissolved
SOLVENT
Substance into which the solute dissolves

19. Solution

20. Suspensions
Substances that don’t dissolve but separate into tiny pieces.
Water keeps the pieces suspended so they don’t settle out.

21. The pH Scale Indicates the concentration of H+ ions Ranges from 0 – 14
pH of 7 is neutral
pH 0 up to 7 is acid … H+
pH above 7 – 14 is basic… OH-
Each pH unit represents a factor of 10X change in concentration
pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6

22. Acids and Bases
An acid is a substance that increases the hydrogen ion concentration in a solution.
Any substance that reduces the hydrogen ion concentration in a solution is a base.
Some bases reduce H+ directly by accepting hydrogen ions.
Strong acids and bases complete dissociate in water.
Weak acids and bases dissociate only partially and reversibly.
There is only 1 molecule out of 554,000,000 water molecules that is dissociated.

23. Acids
Strong Acids have a pH of 1-3
Produce lots of H+ ions

24. Bases Strong Bases have a pH of 11 to 14
Contain lots of OH-ions and fewer H+ ions

25. Buffers
Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization).
Produced naturally by the body to maintain homeostasis
Weak Acid
Weak Base