Chapter 3:
Water and Life
Essential Knowledge
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2.a.3 – Organisms must
exchange matter with the
environment to grow, reproduce,
and maintain organization (3.13.3).
7 Properties of Water
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1)
2)
3)
4)
5)
6)
7)
Cohesive
Adhesive
High surface tension
Stabilizes temperatures
High heat of vaporization
Expands when frozen
Versatile solvent
1) Liquid Water Is Cohesive
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Water sticks to water.
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Why?
• Because the polarity of water results in
hydrogen bonding.
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Contributes to transport of nutrients
(plants)
2) Liquid Water is Adhesive
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Water sticks to other molecules.
Why?
• Hydrogen bonding.
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Plants:
• Water adheres to cell walls (helps pull
water and nutrients through plant)
Water transport in trees uses
Cohesion and Adhesion
3) Water Has A High Surface
Tension
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The surface of water is difficult to
stretch or break.
Why? Hydrogen bonding.
Greater surf tension than most
liquids
4) Water Stabilizes Temperature
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Water can absorb and store a huge
amount of heat from the sun.
Result - climate moderation
Result - organisms are able to
survive temperature changes.
5) Water Has A High Heat Of
Vaporization
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Heat of Vaporization:
• The quantity of heat a liquid must
absorb for 1g of it to convert to a
gaseous state.
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Results:
• Water cools organisms from excessive
heat buildup.
• Why?
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Hydrogen bonding
6) Water Expands When It
Freezes
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The distance between water molecules
INCREASES from the liquid to the
solid form.
Result:
• Aquatic life can live under ice.
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Why?
• Hydrogen bonding
Solids and Liquids
Water
Benzene
Floats
Sinks
States of Matter
Solid
Liquid
Gas
7) Water Is A Versatile Solvent
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Water will form a solution with many
materials.
Considered the best solvent
Why?
• Hydrogen bonding
Solvent
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The dissolving agent.
The material in the greater quantity.
Ex:
• Water
• Alcohols
• Buffers
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Water is the best solvent
• Why? Versatile (can dissolve MOST
solutes)
Solute
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The substance that is dissolved.
The material in the lesser quantity.
Ex:
• Salt
• Sugar
• Kool-aid powder
Hydrophilic Materials
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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
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Materials that repel water.
Hydro - water
phobic - to fear
Have non-polar covalent bonds.
• Remember: In npc bonds, e- are shared
evenly.
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Ex:
• Lipids
• Cell membrane components
Quick Review
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What is cohesion?
What is adhesion?
Name the main reason that water
possesses the properties that it does.
Give an example of each of the
following:
• Solute
• Solvent
Solution Concentration
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Usually based on Molarity.
Molarity - the number of moles of
solute per liter of solution.
Use mass to calculate # of molecules
Moles
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The molecular weight of a substance
in grams.
One Avogadro’s number of
molecules.
• 6.02 X 1023 = 1 mole
One Mole of each
Sugar
Copper Sulfate
Sulfur
Mercury Oxide
Sodium Chloride
Copper
Dissociation of Water
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Water can sometimes split into two
ions.
In pure water the concentration of
each ion is 10-7 M
Dissociation of Water,
Continued
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Adding certain solutes disrupts the
balance between the two ions.
The two ions are very reactive and
can drastically affect a cell.
Acids
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Materials that can release H+ (when
dissolved in water)
pH = 0-7 (6.9)
Example: HCl
HCl
H+ + Cl-
Bases
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Materials that can absorb H+
Often reduce H+ (by producing OH- )
pH = 7.1-14
Example: NaOH, blood (7.4-7.8),
bleach
Neutrals
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Materials that are neither acids nor
bases.
pH = 7 (ish)
• Usually 6.5-7.4
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Ex:
• Urine
pH Scale
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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
pH, cont.
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Acids: pH <7 etc.
Bases: pH >7 etc.
Each pH unit is a 10x change in H+
[H+] + [OH-] = 14
Therefore, if you know the
concentration of one ion, you can
easily calculate the other.
Buffers
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Materials that have both acid and
base properties.
Resist pH shifts.
Cells and other biological solutions
often contain buffers
Buffers, cont.
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Advantage:
• Prevents damage to cell/DNA
• pH changes can denature proteins
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Ex:
• Buffers in blood keep pH around a
slightly basic pH
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Most are acid-base pairs
Summary
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Recognize the chemical structure of water.
Relate the structure of water to its properties.
Identify and discuss the unique properties of
water.
Calculate specific concentrations of solutions
(moles).
Recognize pH and the pH scale.
Recognize acids, bases, and buffers.