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 3
Water and the Fitness of the
Environment
Question?
What molecule Is the most common In living
Cells?
Water - most cells are 70 - 95% water
The Water Planet
Properties Of Water
• Be ready and able to discuss several of
the following properties.
• Focus on definitions and examples.
• Review water structure and H-bonds
from Chapter 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
Water Has A High Surface
Tension
• The surface of water is difficult to stretch
or break.
• Why? Hydrogen bonding.
Water Has A High Specific Heat
• Specific Heat - the amount of heat needed
to raise 1 g of the substance 1 degree C.
• Why?
Hydrogen bonding.
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
• Water can absorb and store a huge
amount of heat from the sun.
• Result - climate moderation
• Result - organisms are able to survive
temperature changes.
Fig. 3-5
Los Angeles
(Airport) 75°
70s (°F)
80s
San Bernardino
100°
Riverside 96°
Santa Ana
Palm Springs
84°
106°
Burbank
90°
Santa Barbara 73°
Pacific Ocean
90s
100s
San Diego 72°
40 miles
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.
Evaporative Cooling
Result:
• Water cools organisms from excessive
heat buildup.
• Why?
Hydrogen bonding
Water Expands When It
Freezes
• The distance between water molecules
INCREASES from the liquid to the solid
form.
• Why?
• Hydrogen bonding
Solids and Liquids
Water
Benzene
Floats
Sinks
States of Matter
Solid
Liquid
Gas
Result
• Aquatic life can live under ice.
Water Is A Versatile Solvent
• Water will form a solution with many
materials.
• Why?
Hydrogen bonding
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.
• One Avogadro’s number of molecules.
6.02 X 1023
One Mole of each
Sugar
Copper Sulfate
Sulfur
Mercury Oxide
Sodium Chloride
Copper
Comment
• AP Biology students should be able to
calculate solutions in Molarity.
Dissociation of Water
• Water can sometimes split into two ions.
• In pure water the concentration of each ion
is 10-7 M
• 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+
• Example: HCl
HCl
H+ + Cl-
Acid Rain
Acid Rain
Bases
• Materials that can absorb H+
• Often reduce H+ by producing OH• Example: NaOH
NaOH
Na+ + OH-
Neutrals
• Materials that are neither acids nor bases.
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.
Fig. 3-9
pH Scale
0
H+
H+
+
– H
H+ OH
+
OH– H H+
H+ H+
Acidic
solution
Increasingly Acidic
[H+] > [OH–]
1
Battery acid
Gastric juice,
2 lemon juice
3 Vinegar, beer,
wine, cola
4 Tomato juice
5
Black coffee
Rainwater
6 Urine
OH–
H+
OH–
H+
OH–
OH– OH– +
H+ H+ H
Neutral
[H+] = [OH–]
8 Seawater
OH–
OH–
H+ OH–
–
–
OH OH
OH–
+
H
Basic
solution
Increasingly Basic
[H+] < [OH–]
Neutral
solution
OH–
Saliva
7 Pure water
Human blood, tears
9
10
Milk of magnesia
11
Household ammonia
12
Household
13 bleach
Oven cleaner
14
Buffers
• Materials that have both acid and base
properties.
• Resist pH shifts.
• Cells and other biological solutions often
contain buffers to prevent damage.
Summary
• Be able to discuss the properties of water.
• Be able to measure solution
concentrations in Molarity.
• Be able to work pH scale questions.