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Life’s Water: Necessary and Abundant. Human H 2 O content:. Even in unusually cold hearty Antarctic bacteria ( e.g. -2C) H 2 O is essential. Life on Europa (Jupiter moon) only considered if H 2 O is present. Water Unlike its Molecular Neighbors. Compound MW BP MP
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Life’s Water: Necessary and Abundant Human H2O content: Even in unusually cold hearty Antarctic bacteria (e.g. -2C) H2O is essential Life on Europa (Jupiter moon) only considered if H2O is present
Water Unlike its Molecular Neighbors Compound MW BP MP H2S Sulfide 34 -60 -85 H2Se Selenide 81 -4 -50 H2Te Telluride 130 -2 -49 H2O Water 18 100 0 As the molecule becomes heavier how should this affect boiling point and melting point?
Unusual Physical Properties of H2O High surface tension Adhesion – sticks to other molecules Cohesion – sticks to itself
Water Hydrogen Bonding: Weak But Abundant Distance for: Covalent H-bonding Non-interacting Where is H-bonding on this graph? Van der Waals radius Van der Waals Radius: distance from nucleus to effective electron surface
Hydrogen Bonding in Water Oxygen Electronic configuration? Bond angle?
Relative Bond Strengths 400 Where do dipole-dipole interactions fit into this ranking? 100 20 0.1
Hydrogen-Bonding Requirement Differential electronegativity Name the following interactions: S – H - - - - - S
Water: the Universal Solvent Polar solvents weaken electrostatic interactions
Dielectric Solvent Constants1 1Dielectric solvent constant is a measure of the ability of a solvent to diminish electrostatic attraction between dissolved ions
Hydrophobic Effect Exclusion of non-polar substances from a water phase Entropy driven ∆G = ∆H - TΔS
Single Tail Amphipathic Molecules: Micelles What is the driving force for this reaction?
Driving Force for Protein Folding: Hydrophobic Effect Amphipathic molecules contain both hydrophobic and hydrophilic portions
pH Versus pKA Is a molecule always charged or uncharged?
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.
Acetic Acid Titration Curve What is the effective buffering range?
Henderson-Hasselbalch Equation pH = pKA – log [HA]/[A-] pKA = -log KA and pH = -log [H+] 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-]
Inverse Relationship: [H+] and [OH-] pH Value of Biological Fluids H2O ↔ H+ + OH- K = [H+][OH-]/[H2O] KW = K[H2O] = [H+][OH-] KW = 10-14 = [H+][OH-]
Water Acidification CO2 + H2O ↔ HCO3- + H+
Chapter 2 Problems: 1-15, 21, 33, 35, 41, 53, 55 and 60