THE IMPORTANCE OF WATER TO LIFE

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THE IMPORTANCE OF WATER TO LIFE
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Hydrogen Bonds Give Water Unique Properties

• Water molecules are polar molecules
• Unequal sharing of electrons V-like shape
• They can thus form hydrogen bonds with each other
  and with other polar molecules
• Each hydrogen bond is very weak
• However, the cumulative effect of enormous
  numbers can make them quite strong
• Hydrogen bonding is responsible for many of the
  physical properties of water

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HYDROGEN BONDING DRAW 2-3 MOLECULES OF WATER
INDICATE THE HYDROGEN BONDS
Not effective over long distances
WEAK BONDS
Formed by the attraction of opposite partial
electric charges between two polar molecules
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COHESIVE PROPERTIES
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Heat vs Temperature

• Heat is a measure of the total amount of kinetic
  energy due to molecular motion in a body of
  matter.
• Calorie the amount of heat it takes to raise the
  temperature of 1g of water by 10C
• Kilocalorie 1,000 calories
• Joule (J) one joule 0.239 calories and 1
  calorie 4.184J
• Temperature the intensity of heat due to the
  average kinetic energy of the molecules.
• We will use Celsius to indicate temperature

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THERMAL PROPERTIES
High Heat of Vaporization
High Specific Heat
Water absorbs a lot of heat, hydrogen bonds
break, then water turns to vapor then
evaporates.
Water can absorb or release a lot of heat without
changing its own temperature by very much. Its
ability to store heat
Makes water a good coolant
Have to add a lot of heat to change its temp.
Heat needed for the evaporation of water in sweat
is taken from the tissues of the skin
Helps keep oceans relatively stable
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WATER AS ICE, FLOATS
Ice
Liquid water
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SOLVENT PROPERTIES
Most of the important molecules in and out of the
cell are polar molecules. These molecules create
solutions that enable for biochemical processes
to occur.
Water is a versatile solvent because of its
polarity
Protein synthesis glycolysis
Gas Exchange
Salt dissolves when all ions have separated from
the crystal
Water forms a hydration shell around each solute
ion.
Light independent processes of photosynthesis
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HYDROPHILLIC vs HYDROPHOBIC

• Hydrophillic

• Hydrophobic

• Molecules that love water
• With positive or negative charges including polar
  molecules

• Molecules that fear water
• Do not have positive or negative charges are
  nonpolar

EX all substances that dissolve in water like
glucose
EX all substances that do not dissolve in water
like fats oils
If substances are soluble in water can be freely
transported in the blood plasma. Ex glucose
amino acids, sodium chloride If they are
hydrophobic they are transported inside a
lipoprotein complex. EX fats and cholesterol
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Solute Concentration in Aqueous Solutions

• Molecular mass sum of the masses of all the
  atoms in a molecule. number of daltons
• Measuring is done in moles6.02 x 1023
• Once the molecular mass of a molecule is
  determined, that number is used with a unit in
  grams.

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How would you make 1 liter of a 1M solution of
sucrose (C12H22O11)

• Review Avogadros number (a mole)
• There are 6.02 x 1023 daltons in 1g.

Carbon has an atomic mass of 12 there are 12
carbons so 12 x 12 144
Hydrogen has an atomic mass of 1 there are 22
hydrogens so 1 x 22 22
Oxygen has an atomic mass of 16 there are 11
oxygens so 16x 11 176
For a total of .342 daltons
So, this means you would need 342g of sucrose in
a liter of 1M sucrose solution
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Calculate the solutions of sucrose (C12H22O11)
Solution Grams of Sucrose Total Volume in Flask
0.2 M
0.4M
0.6M
0.8M
1.0M 342g 1,000mL
68.4g
1,000mL
136.8g
1,000mL
205.2g
1,000mL
273.6g
1,000mL
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Water Ionizes

• Covalent bonds within a water molecule sometimes
  break spontaneously

Simplified version

• This process of spontaneous ion formation is
  called ionization
• It is not common because of the strength of
  covalent bonds

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BELOW IS A BEAKER OF DISTILLED WATER
WHAT IS THE CHEMICAL FORMULA FOR THIS BEAKER OF
DISTILLED WATER?
H2O H2 H3O OH-
H2O H OH-
Simplified version
Is the concentration of water in the beaker the
same as the total concentration of H OH- ?

NO
What does it mean to be at equilibrium?
The reactions is flowing back forth, but there
is no longer any net gain in either the
concentration of the products or the reactants.
Which is in higher concentration in this beaker
H2O or H OH- ?
H2O
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pH

• A convenient way to express the hydrogen ion
  concentration of a solution

• The pH scale is logarithmic
• A difference of one unit represents a ten-fold
  change in H concentration
• Acid
• Dissociates in water to increase H concentration
  
• Base
• Combines with H when dissolved in water

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Remember

• The pH scale is logarithmic.
• A change in one pH number actually represents a
  tenfold change in hydrogen ion concentration
• EX pH of 3 is actually ten times more acidic
  than a pH of 4.

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CALCULATE THE RATIO OF DISSOCIATED TO INTACT
WATER MOLECULES IN A BEAKER OF DISTILLED WATER OF
pH at 250 C
If pH 7, then the concentration of hydrogen H
1 x 10-7 , which is the same as
H 1/10,000,000 , which is the same as
Saying there is 1 dissociated molecule of H2 O
for every 10 million intact H2 O molecules in the
beaker of distilled water on the table.
IN OTHER WORDS.
If you could reach in pick out a single
molecule from the beaker of water, 9,999,999
times out of 10,000,000 you would pull out a
molecule of H2 O 1 out of 10,000,000 times you
would pick out a hydrogen ion.
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pH chart (from WS)
pH level Exponetial notation Decimal notation Fraction notation OH-
1 1 X 10-1 0.1 1/10 1 X 10-13
4 1 X 10-4 0.0001 1/10,000 1 X 10-10
7 1 X 10-7 0.0000001 1/10,000,000 1 X 10-7
10 1 X 10-10 0.0000000001 1/1,000,000,000 1 X 10-4
14 1 X 10-14 0.00000000000001 1/10,000,000,000,000 1 X 10-0
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DISCUSSION QUESTIONS
Considering the equation H2O H OH- at
equilibrium to answer the following questions
Does the equation tend to one direction of the
other? If so, which direction does it tend to go?
This reaction tends towards the left
Which is in higher concentration in the above
equation (H2O) or (H OH- )
H2O
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DISCUSSION QUESTIONS
How many times different is a change in one unit
of the pH scale?
10X more or less concentrated
Whats the difference in hydrogen concentration
between pH5 pH2?
pH2 has 1,000 times the concentration of H than
a solution of pH5
What is the difference between a strong acid/base
a weak acid/base?
A strong acid/base dissociates readily because
the differences in the electronegativity of the
ions are greater a weak acid/base has atoms that
are not as different in their electronegativity
so they dont tend to the dissociated side of the
equation as easily.
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DISCUSSION QUESTIONS
Which acids/bases are weaker which are stronger
--- HCl, NH3, H2CO3 NaOH?
Cl Na both have very high electronegativity
they are both in column VII of ther periodic
table with nearly full valence shells - so they
tend to dominate the electrons of H or OH- since
the electronegativity of these atoms are very
low. This huge difference in electronegativity
causes a strong tendency for NaOH and HCl to
dissociate. When the H or OH- dissociate from
the Na the Cl they are free to react with other
molecules making them strong acids bases. N
CO3 dont have as strong of an electronegative
difference with H since they are in columns
IV-VI. Because of their lower electronegativity
they do not dissociate as readily as HCl NaOH
so they are considered weaker acids bases.
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Buffers

• Hydrogen ion reservoirs that take up or release
  H as needed
• The key buffer in blood is an acid-base pair
  (carbonic acid-bicarbonate buffering system)

Response to a rise in pH
Response to a drop in pH
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Acid Precipitation