Business

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Business

• Buy your lab manual ASAP (3.00 cash),
• Friday, 1 - 2, BI261,
• Quiz next Thursday covering reading materials
  through that day, i.e. Proteins,
• Lecturesupdated by morning of the lecture.

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Water is common to all life on Earth.
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H2O Polarity

• polar molecule,
• each water molecule can form hydrogen bonds to as
  many as four other molecules.

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H2O Bonding

• Forms a rough tetrahedron,
• hydrogens at two corners,
• unpaired electrons at two corners.

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Polar Molecules

• when electrons are shared unevenly in a covalent
  bond, the bond is polar,
• substances with polar bonds are hydrophilic.

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Effects of Waters Polarity

• The polarity of water molecules results in
  hydrogen bonds,
• Organisms depend on the hydrogen bonding of of
  water molecules,
• cohesion,
• adhesion,
• Water moderates temperatures on Earth,
• Water is the solvent of life.

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Cohesion

• water molecules stick together because of
  hydrogen bonding,
• hydrogen bonds in liquid water last only a few
  trillionths of a second,
• collectively, the hydrogen bonds hold the water
  together.

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Cohesion
Evaporation from leaves pulls water up from the
roots.
An unbroken transpiration stream is required
for water transport.
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Adhesion

• water also sticks to other substances.

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Surface Tension

• a measure of how difficult it is to stretch or
  break the surface of a liquid,
• water has a high surface tension due to the
  hydrogen bonding of surface molecules.

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Water - Air Interface

• water molecules in solution have attractions in
  all directions,
• at the surface, nothing counterbalances the
  downward pull.

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Water Moderates Temperatures

• water is effective as a heat bank because it can
  absorb or release a relatively large amount of
  heat with only a small change in its own
  temperature.

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Specific Heat

• the amount of heat that must be absorbed or lost
  for 1 g of a substance to change its temperature
  1o C,
• 
  
• ...calorie the amount of heat it takes to raise
  1 g of H2O by 1o C.

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Specific Heat Examples
Substance
Specific Heat

• Alcohol 0.58
• Gold 0.03
• Granite 0.19
• Iron 0.10
• olive oil 0.47
• water 1.00

cal/g oC
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Hydrogen Bonds Again

• waters high specific heat is due to the
  breakdown and formation of hydrogen bonds,
• heat energy is absorbed or dissipated by the
  numerous hydrogen bonds.

Remember heat is a measure of total quantity of
kinetic energy due to molecular motion in a body
of matter
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Moderates Temperatures

• absorbs heat from the sun during the day,
• prevents drastic high temperatures,
• slowly releases heat at night,
• prevents drastic cold temperatures,
• moderates large bodies of water and nearby land
  masses,
• also moderates temperatures within organisms.

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Heat of Vaporization

• is the amount of heat a liquid must absorb for 1
  g of it to be converted from the liquid to the
  gaseous state,
• 580 calories of heat are required to convert 1 g
  of water to steam.

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Heat of Vaporization Examples
Substance
HV

• Methanol 1100
• Ethanol 854
• Acetone 523
• Benzene 394
• Butane 381
• water 2,260

cal/g oC
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Climate

• waters high heat of vaporization helps moderate
  Earths climate,
• the extreme heat absorbed by tropical seas is
  consumed during the evaporation of surface water,
• as moist tropical air circulates pole-ward, heat
  is released as it condenses to form rain.

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Evaporative Cooling

• occurs because the hottest molecules are most
  likely to leave as gas,

• bodies of water,
• animals,
• plants.

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Ice Floats

• water is less dense as a solid than it is as a
  liquid,

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Oceans and Lakes Dont Freeze Solid

• if ice sank, as does most solids, bodies of
  water would freeze,
• floating ice insulates the water, maintaining
  temperatures near 0o C.

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Water is the Solvent of Life

• a liquid that is a complete mixture of two or
  more substances is called a solution,
• the dissolving agent is the solvent,
• the dissolved substance is the solute,
• aqueous solution is one in which water is the
  solvent.

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Water is Not a Universal Solvent

• or else nothing would hold it,
• biological systems use hydrophobic molecules to
  contain water.

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Mole

• the standard reference unit for the amount of
  each pure chemical substance is the molecular
  weight of the substance taken in grams,
• H2O H is 1.008 Dalton, O is 16 Dalton,
• molecular weight of H2O is 18.016,
• ...one mole of H2O is equal to 18.016 grams.

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Avagadros Number

• the number of atoms or molecules in that
  quantity of a substance that, expressed in grams,
  is numerically equivalent to the atomic weight
  6.02 X 1023,
• or one mole 6.02 X 1023 atoms or molecules.

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Molarity

• the number of moles of solute per liter of
  solution,
• Sugar, C12H22O16 (MW 342),
• 1 mole of sugar 342 grams,
• 342 grams in a liter of water 1 M, a 1 molar
  solution.

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Self Ionization of Water
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H is a Proton

• in pure water, only one in 554 million molecules
  is auto-ionized,
• H (hydrogen ions) in pure water is 10-7 M (at
  25o C),
• OH- (hydroxide ions) is the same.

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Acids

• acids increase H in aqueous solutions,
• when HCl (hydrocloric acid) is added to water,

HCl ----gt H Cl-
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Bases

• bases reduces H in aqueous solutions,
• when NaOH (hydrocloric acid) is added to water,

OH- H ----gt H2O
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Bases

• bases reduces H in aqueous solutions,
• when NH3 (ammonia) is added to water,

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Strong/Weak Acids

• strong acids dissociate completely when mixed
  in water,
• HCl ----gt H Cl-
• weak acids the binding and dissociation of the
  H ion is readily reversible,

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Strong/Weak Bases

• strong bases dissociate completely when mixed
  in water,
• NaOH ----gt Na OH-
• weak bases the binding and dissociation of the
  OH- ion is readily reversible,

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pH is the measure of H

• acid and base refer to compounds and ions,
• acidic and basic refer to solutions.

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Hand OH- ions

• in any aqueous solution the concentration of the
  H and OH- ions is constant at 10-14 M,
• H OH- 10-14 M
• if H is 10-7, then OH- is 10-7,
• ...if H is 10-5, then OH- is 10-9.

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pH

• to conveniently express the variation in the
  concentrations of H and OH- ions, scientists use
  the pH scale,
• pH (potential of Hydrogen) is the negative
  logarithm of H ,
• pH -log10 H

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pH -log10 H
pH -log10 10-7 -(-7) 7
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pH and H are Inversely Proportional
pH -log10 10-12 -(-12) 12
pH -log10 10-7 -(-7) 7
pH -log10 10-4 -(-4) 4
pH -log10 10-2 -(-2) 2
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10 Fold Steps

• each pH unit represents 10 fold difference in H
  and OH- ions,
• a solution of pH 3 is not twice as acidic as a
  solution of pH 6,
• it is 103, or 1000 times more acidic,
• Small changes in pH represent large changes in H
  and OH- concentrations.

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Buffers

• a solution characterized by the ability to
  resist changes in pH when limited amounts of acid
  or base are added to it,

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Buffers Minimize pH Changes
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To Do

• Read through pp. 48-55, as assigned in the
  syllabus,
• Note, for Tuesday, read pp. 58-60.