Should we control a chemical that:







Causes excessive sweating and vomiting.
Is a major component in acid rain.
Can cause severe burns in its gaseous state.
Accidental inhalation can kill you.
Contributes to erosion.
Decreases the effectiveness of car brakes.
Has been found in tumors of terminal cancer
patients.
What is the chemical?

Dihydrogen monoxide

Otherwise known as H2O
Chapter 2
Water and the Fitness of
the Environment


Three-quarters of the Earth’s surface is submerged in
water
The abundance of water is the main reason the Earth
is habitable



Water is the biological medium here on Earth
All living organisms require water more than any other
substance
Most cells are composed of 70-95% water.
Figure 3.1
States of Matter
Solid
Liquid
Gas
Water is a polar molecule (oxygen is more electronegative
than hydrogen creating a partial negative charge on oxygen
and a partial positive charge on hydrogen)
The polarity of water molecules results in unique
properties. Each water molecule can form 4
hydrogen bonds. The extraordinary qualities of
water are emergent properties resulting from
the hydrogen bonding.
–
+
H
+  – H+
–
–
+
Figure 3.2
Liquid Water Is Cohesive
Water sticks to water.
 Why?
Because the polarity of water results in hydrogen
bonding.

Liquid Water is Adhesive
Water sticks to other molecules.
 Why?
Hydrogen bonding.

Water transport in trees uses
Cohesion and Adhesion

Cohesion

Helps pull water up through the microscopic
vessels of plants
Water conducting cells
Figure 3.3
100 µm
Water Has A High Surface
Tension


The surface of water is difficult to stretch or
break.
Why? Hydrogen bonding.
Figure 3.4
Water Has A High Specific Heat
Specific Heat - the amount of heat needed to
raise 1 g of the substance 1 degree C.
 A measure of how well a substance resists
changing its temperature when it absorbs or
releases heat.
 Why?
Hydrogen bonding.

Heat is absorbed when hydrogen bonds break
 Heat is released when hydrogen bonds form

Heat

Total quantity of kinetic energy due to
molecular motion.
Temperature

Measures the
average speed of
the molecules.
Celsius Scale




Will be used for most of our temperature
measurements.
O oC - water freezes
100 oC - water boils
37 oC - human body
Water Stabilizes Temperature






Because of its high specific heat, water can absorb and store a
huge amount of heat from the sun.
Result - climate moderation
Water stabilizes air temperatures by absorbing
heat from the Sun and from air that is warmer and
releasing the stored heat to air that is cooler.
Water is effective as a heat bank because it can absorb or
release a relatively large amount of heat with only a slight
change in its own temperature. This is the reason coastal
areas generally have milder climates than inland regions.
Result – stabilized ocean temperatures create a favorable
environment for marine life
Result - organisms are able to survive temperature changes.
Because organisms are made primarily of water, they are
able to resist changes in their own temperatures.
Water Has A High Heat Of
Vaporization



Heat of Vaporization: the quantity of heat a
liquid must absorb for 1g of it to convert to a
gaseous state.
Water must absorb a large amount of heat to
break its hydrogen bonds from a liquid to a gas.
This helps to moderate
Earth’s climate.
Evaporative Cooling
Evaporative Cooling
Result:

As a liquid evaporates, the surface of the liquid
that remains behind cools down.
Contributes to the stability of temperature in lakes
and ponds
 Provides a mechanism that prevents terrestrial
organisms from overheating EX. sweating

Why?
Hydrogen bonding

Water Expands When It Freezes




The distance between water molecules
INCREASES from the liquid to the solid form.
Why?
Hydrogen bonding
Hydrogen bonds keep the water molecules far
enough apart that they lock into a crystalline
lattice structure, making ice about 10% less
dense than water at 4 degrees Celsius.
Solids and Liquids
Water
Benzene
Floats
Sinks
Result

Floating ice insulates the liquid water below,
preventing it from freezing and allowing aquatic
life to live under the frozen surface.
e 3.5
Hydrogen
bond
Ice
Liquid water
Hydrogen bonds are stable
Hydrogen bonds
constantly break and re-form
Water Is The Universal Solvent
Water will form a solution with many materials.
 Why?
Hydrogen bonding

Water is polar (unequal sharing of electrons)
ionic substances are soluble in water
polar dissolves polar ( sugar in water)
Nonpolar substances do not dissolve in water
EX. lipids
Solution
Homogeneous mixture of two or more substances.
Solvent
The dissolving agent.
The material in the greater
quantity.
Solute
The substance that is
dissolved.
The material in the lesser
quantity.
Hydrophilic Materials




Materials that dissolve in water.
Hydro - water
philic - to like or love
Have ionic or polar regions (polar covalent
bonds) on their molecules for H+ bonds.
Hydrophobic




Materials that repel water.
Hydro - water
phobic - to fear
Have non-polar covalent bonds. Ex - lipids.
Without Water Life
Would Not Be
Possible!!
Solution Concentration


Usually based on Molarity.
Molarity - the number of moles of solute per
liter of solution.
Moles



The molecular weight of a substance in grams.
A mole of one substance has exactly the same
number of molecules as a mole of another
substance.
Avogadro’s number is the number of
molecules in a mole.
6.02 X 1023
One Mole of each
Sugar
Copper Sulfate
Sulfur
Mercury Oxide
Sodium Chloride
Copper
Dissociation of Water

Water can sometimes split into two ions.

In pure water the concentration of each ion is 10-7


Adding certain solutes disrupts the balance
between the two ions.
The two ions are very reactive and can
drastically affect a cell.
Acids



Materials that can release H+
increases the hydrogen ion concentration of a
solution
Example: HCl
HCl
H+ + Cl-
Acid Rain
Acid Rain
Bases



Materials that can absorb H+
Often reduce H+ by producing OHExample: NaOH
NaOH
Na+ + OH-
pH Scale

A logarithmic scale for showing H+
concentration
pH = - log [H+]
pH Scale
Example:
For a neutral solution:
[H+] is 10-7
or - log 10-7
or - (-7)
or 7

Acids: pH <7 etc.
Bases: pH >7 etc.

Each pH unit is a 10x change in H+

Comment


[H+] + [OH-] = 14
Therefore, if you know the concentration of one
ion, you can easily calculate the other.
Buffers

The internal pH of most living cells

Must remain close to pH 7
Buffers



Materials that have both acid and base
properties.
Resist pH shifts.
Cells and other biological solutions often
contain buffers to prevent damage.
 Buffers
Are substances that minimize changes in the
concentrations of hydrogen and hydroxide ions in
a solution
 Consist of an acid-base pair that reversibly
combines with hydrogen ions

The Threat of Acid Precipitation

Acid precipitation
Refers to rain, snow, or fog with a pH lower than
pH 5.6
 Is caused primarily by the mixing of different
pollutants with water in the air
 Caused primarily by the presence in the
atmosphere of sulfur oxides and nitrogen oxides,
created by the burning of fossil fuels


Acid precipitation

Can damage life in Earth’s ecosystems
0
1
2
More
acidic
3
4
Acid
rain
5
6
Normal
rain
7
8
9
10
11
12
13
14
Figure 3.9
More
basic