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Life’s Water: Necessary and Abundant

Explore the unique physical properties of water, its importance in sustaining life, and the significance of hydrogen bonding. Learn about the impact of molecular weight on boiling and melting points, the role of water as a universal solvent, and the concept of hydrophobic effect in cellular processes.

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Life’s Water: Necessary and Abundant

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  1. 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

  2. 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?

  3. Unusual Physical Properties of H2O High surface tension Adhesion – sticks to other molecules Cohesion – sticks to itself

  4. 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

  5. Hydrogen Bonding in Water Oxygen Electronic configuration? Bond angle?

  6. DNA Base Pair Hydrogen Bonding

  7. Relative Bond Strengths 400 Where do dipole-dipole interactions fit into this ranking? 100 20 0.1

  8. Hydrogen-Bonding Requirement Differential electronegativity Name the following interactions: S – H - - - - - S

  9. Water: the Universal Solvent Polar solvents weaken electrostatic interactions

  10. Dielectric Solvent Constants1 1Dielectric solvent constant is a measure of the ability of a solvent to diminish electrostatic attraction between dissolved ions

  11. Hydrophobic Effect Exclusion of non-polar substances from a water phase Entropy driven ∆G = ∆H - TΔS

  12. Single Tail Amphipathic Molecules: Micelles What is the driving force for this reaction?

  13. Double Tail Amphipathic Molecules: Bilayer

  14. A Bilayer Limits Movement of Polar Substances

  15. Driving Force for Protein Folding: Hydrophobic Effect Amphipathic molecules contain both hydrophobic and hydrophilic portions

  16. pH Versus pKA Is a molecule always charged or uncharged?

  17. Ka/pKa Values

  18. 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.

  19. Acetic Acid Titration Curve What is the effective buffering range?

  20. 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-]

  21. 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-]

  22. Water Acidification CO2 + H2O ↔ HCO3- + H+

  23. Acids to Buffer at Any pH

  24. Chapter 2 Problems: 1-15, 21, 33, 35, 41, 53, 55 and 60

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