This has been the 1592nd visit to this site since August 26, 1996.

Life on earth probably evolved in water. Cells are 70-95% water and water covers 75% of the earth's surface.

A. WATER IS STICKY AT THE MOLECULAR LEVEL

COHESION = property of being held together by H bonds
transitory but there are so many and constantly reforming.(see Fig. 3.1)

Affects water movement in plants(see Fig. 3.2)

ADHESION = clinging of water to hydrophilic surfaces
like glass or cellulose

SPECIFIC HEAT = amount of heat absorbed to raise one gram of a substance one degree Celsius.

for water = one calorie (1 cal / g water / degree C)

KINETIC ENERGY = the energy of motion

HEAT = Total kinetic energy due to molecular motion

TEMPERATURE = measure of heat intensity due to the average kinetic energy of molecules in a body of matter

WHY DOES WATER HAVE A HIGH SPECIFIC HEAT?

Because of all those H bonds
They absorb heat to break (and release heat when they form)
Therefore much heat is needed to disrupt H bonds before water molecules can move faster (= increase in temp.)

Consequences:

Takes a lot of heat to change the temperature of water

1) Areas around large bodies of water have less variable climates (compare Colorado and California)
2) Marine environment more stable than the land
3) Temps. on earth are suitable for life

VAPORIZATION (= evaporation) = liquid to gas
Molecules with a lot of kinetic energy can escape into air
Heat of vaporization for water is high = 540 calories / g.

EVAPORATIVE COOLING = loss of molecules with high kinetic energy --- means temp. of liquid will drop

Consequences:

MODERATES earth's climate esp. in tropical waters

Our bodies are cooled by the evaporation of sweat (Fig. 3.4)

(See fig. 3.5 and 3.6)
As water cools it loses heat until the molecules don't have enough kinetic energy to even break H bonds. Thus it is held in a lattice. ICE FLOATS!

Consequences:

Ice forms on the tops of lakes and insulates the water below
Bodies of water would freeze solid if they froze from the bottom up

SOLVENT = dissolving agent (e.g. H2O)

SOLUTE = substance dissolved in a solution (e.g. NaCl)

Ionic and polar compounds dissolve in water by interacting with H-BONDS of water.

These compounds are HYDROPHILIC (water loving)

Non-polar compounds are not soluble in water and are HYDROPHOBIC (water hating)

A. 1) MOLE = 1 gram molecular weight of a substance

e.g. for NaCl

Atomic mass of Na = 23

Atomic mass of Cl = 35
__________________________
Total = 58 daltons

Therefore, 1 mole of NaCl = 58 grams

a 2 M solution of NaCl = 116 grams (2 x 58) of NaCl/L
(M = molar, L = liter)

We think of water as dissociating:

H2O ---> H+ + OH-

At equilibrium in water:
[H+] = [OH-] = 1/10,000,000 M = 10-7; M

[] = concentration

e.g. Hydrochloric acid: HCl ---> H+ + Cl-

e.g. Sodium hydroxide: NaOH --> Na+ + OH-
OH- then reacts with H+ to form water

[H+] and [OH-] can vary over a huge range
therefore we use a LOG SCALE
pH = -log10 of [H+]

For neutral solution: [H+] = 10-7 M
pH = -log10 of 10-7 M = 7

examples (see Fig. 3.9):

Coffee pH = -log10 of 10-5 M = 5

Tomato juice pH = -log10 of 10-4 M = 4

Lemon juice pH = -log10 of 10-2 M = 2

Each unit on the pH scale is 10x difference, thus lemon juice is 100 x more acid than tomato juice

= Rain more acidic than pH of 5.6

Occurs when S and N oxides react with H2O to form acids
These oxides come from cars and power plants that burn fossil fuels

Affect mineral mobility in soils,

Kills fish and amphibians (Lakes in Adirondack Mtns., pH < 5)

Levels have gone down in some areas due to pollution control (but not here).

1) Drive less (mass transport, bikes, walking)
2) Use less energy to heat and cool homes (insulate more, wear a sweater instead of turning up the heat etc.....)