Download Properties of Water

Properties of Water
A.P. Biology
Water Video
Water: The Liquid of Life
70-90% of living cells is water
¾ of Earth is covered with water
Life cannot be sustained without it
Water is a polar covalent molecule which
allows water to Hydrogen bond with itself
and other polar and charged particles
All of water’s properties come from it being
dipolar and it’s ability to H bond with other
molecules
Properties
Property
1. Cohesive (sticks to self) &
Adhesive (sticks to other
things) due to H-bonding
2. Unique Density Property
Ice (solid form) is less dense
than water (liquid) due to Hbonds forming as molecules
slow down - keeping
molecules more spread out)
Why necessary to life on
earth?
1a.Water can be transported
against gravity in plants –
allows plants to be the base
of the foodweb
1b.Causes surface tension and
provides for aquatic
ecosystems
2. Ice floats allowing oceans and
lakes to freeze from the top
down allowing living things
to live underneath
Cohesion
Adhesion
Ice Formation
3. Almost Universal Solvent
(dissolves all polar and ionic
cmpds.) due to water
surrounding molecules and
pulling them apart – partially
neg. O is attracted to pos. and
partially pos. H is attracted to
neg.
4. High Specific Heat (can absorb
or lose a lot of heat before
temperature changes) – as
heat is added, energy is used
to break H bonds before
molecules can move faster
(temp. increase)
3a. Allows salts, proteins, to be
dissolved in cells, blood, sap
3b. Allows blood and sap to carry
oxygen, nutrients,
messengers
3b. Allows biological fluids to act
as buffers
5. High Heat of Vaporization
(takes longer to evaporate)
since must break H bonds
before can move fast enough
to evap.)
5a. Cools body since molecules
with highest energy (temp.)
leave
5b. Cools aquatic ecosystems
4. Maintains moderate temp. on
Earth
Helps maintain body
temperature
Dissolving Ability of Water
Water and pH
• 1/554,000,000 molecules of water dissociates
• Water dissociates into H+ and OH• pH is the relative concentrations of H+ and OH- (pH is
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acutally the concentration of H+) -log [H+]
Acid – donates an H+ or accepts an OHBase – accepts an H+ or donates an OH[H+][OH-] = 10-14 so if [H+] = [OH-] then H+ = 10-7 so
pH = 7
As H+ increases, the pH decreases
Each pH unit is a 10 fold difference in [H+]
pH Practice Problems
• [H+] is 10-4 M, what is [OH-]?
• If [H+] is 10-11 M, what is the pH? Is it acidic or basic?
• If [OH-] is 10-6 M, what is the pH?
• How much greater is [H+] in a solution that is pH 2 vs.
pH 6?
Buffers
• Which lines represent the buffers?
• Buffers keep the pH relatively constant
• Buffers are salts or weak acids or bases
that can accept and donate H+ reversibly
or salt solutions that can accept H+ or OH• Buffers are important to maintain pH in
organisms and ecosystems
Diversity of Carbon – 4 valence electrons
Can get a lot of variation
A. Length
B. Arrangement and Shape – Isomers –
molecules with the same formula but
different arrangements – different shape
and different function
C. Number of Double Bonds
A. Double bonds cause kinks in the chain not
allowing the molecules to pack together as
closely so they don’t solidify at room temp.
B. Atoms can’t swivel around double bonds
causing enantiomers.
Isomers
Double vs. Single Bonds
D. Functional Groups
A. Hydroxyl – OH – form alcohols – make
sugars dissolvable
B. Carbonyl – C=O – form aldehydes or ketone
C. Carboxyl groups – COOH – forms carboxylic
acids – fatty acids, amino acids
D. Amino groups – NH2 - form amines – amino
acids
E. Sulfhydryl groups – SH - forms thiols – cross
linking proteins
F. Phosphate groups – PO4- form phosphates
– important part of nucleotides and ATP
G. Methyl groups – CH3 – important for
controlling DNA expression
-SH Groups
Amino and
Carboxyl
Groups
Methyl Groups