Chapter 2 Water: the Medium of Life. Outline. What are the properties of water ? What is pH ? What are buffers, and what do they do ? Does water have a unique role in the fitness of the environment ?. 2.1 What Are the Properties of Water?. Water has unusual properties:
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Figure 2.1 The structure of water.
A comparison of ice and water, in terms of H-bonds and Motion
Figure 2.2 The structure of normal ice.
The fluid network of H bonds linking water molecules in the liquid state.
Van der Waals
London forces – instantaneous dipole
H-Bonds – H must be covalent to N or O
Hydrophobic interactions – entropy from solvent reorganization
Figure 2.4 Hydration shells surrounding ion in solution.
Figure 2.6 Nonpolar molecules increase the entropy of solvent water.
Figure 2.7 (a) Sodium palmitate is an amphiphilic molecule.
(b) Micelle formation by amphiphilic molecules in aqueous solution.
Figure 2.9 The ionization of water.
Figure 2.10 The hydration of H3O+.
Consider a weak acid, HA
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Titration curves illustrate the progressive dissociation of a weak acid.
The titration curves of several weak acids.
The titration curve for phosphoric acid.
A buffer system consists of a weak acid, HA and its conjugate base, A- or a weak base A and its conjugate acid HA+.
pH – rate profile
Figure 2.15 Enzymatic activity vs pH
(a) Pepsin is a protein-digesting enzyme active in gastric fluid.
(b) Fumarase is a metabolic enzyme found in mitochondria.
(c) Lysozyme digests the cell walls of bacteria (found in tears).
Figure 2.17 The structure of HEPES (an example of a buffer used in the laboratory), in its fully protonated form. pKa = 7.47