life’s water: necessary and abundant human h 2 o content: life on europa (jupiter moon) only...
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Life’s Water: Necessary and Abundant
Human H2O content:
Life on Europa (Jupiter moon) only considered if H2O is present Even in unusually
cold hearty Antarctic bacteria (e.g. -2C) H2O is essential
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Compound MW BP MP
H2S Sulfide 34 -60 -85H2Se Selenide 81 -4 -50H2Te Telluride 130 -2 -49
H2O Water 18 100 0
Water Unlike its Molecular Neighbors
As the molecule becomes heavier how should this affect boiling point and melting point?
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Unusual Physical Properties of H2O
Adhesion – sticks to other molecules
Cohesion – sticks to itself
High surface tension
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Water Hydrogen Bonding: Weak But Abundant
Distance for:
Covalent
H-bonding
Non-interacting
Van der Waals radius
Van der Waals Radius: distance from nucleus to effective electron surface
Where is H-bonding on this graph?
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Oxygen Electronic configuration? Bond angle?
Hydrogen Bonding in Water
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DNA Base Pair Hydrogen Bonding
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100
400
200.1
Relative Bond Strengths
Where do dipole-dipole interactions fit into this ranking?
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Hydrogen-Bonding Requirement
Differential electronegativity
S – H - - - - - SName the following interactions:
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Water: the Universal Solvent
Polar solvents weaken electrostatic interactions
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Dielectric Solvent Constants1
1Dielectric solvent constant is a measure of the ability of a solvent to diminish electrostatic attraction between dissolved ions
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Exclusion of non-polar substances from a water phase
Entropy driven ∆G = ∆H - TΔS
Hydrophobic Effect
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Single Tail Amphipathic Molecules: Micelles
What is the driving force for this reaction?
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Double Tail Amphipathic Molecules: Bilayer
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A Bilayer Limits Movement of Polar Substances
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Amphipathic molecules contain both hydrophobic and hydrophilic portions
Driving Force for Protein Folding: Hydrophobic Effect
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Is a molecule always charged or uncharged?
pH Versus pKA
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Ka/pKa Values
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Le Chatelier’s Principle
When a system in a state of dynamic equilibrium is acted upon by some outside stress, the system will, if possible, shift to a new position of equilibrium in order to minimize the effect of the stress.
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Acetic Acid Titration Curve
What is the effective buffering range?
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Conceptionally: pKA is the pH at which the ionized
and unionized forms are equal. HA ↔ H+ + A-
KA = [A-][H+]/[HA]
KA[HA]/[A-] = [H+]
log KA + log [HA]/[A-] = log [H+]
pH = pKA – log [HA]/[A-]
Henderson-Hasselbalch Equation
pH = pKA – log [HA]/[A-]
pKA = -log KA and pH = -log [H+]
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pH Value of Biological Fluids
Inverse Relationship: [H+] and [OH-]
H2O ↔ H+ + OH-
K = [H+][OH-]/[H2O]
KW = K[H2O] = [H+][OH-]
KW = 10-14 = [H+][OH-]
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CO2 + H2O ↔ HCO3- + H+
Water Acidification
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Acids to Buffer at Any pH
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Chapter 2 Problems:
1-15, 21, 33, 35, 41, 53, 55 and 60