Chapter 3 Water
A. Structure
individual molecule
distorted tetrahedral shape
dipole moment
aggregate structure
B. Properties
specific heat – high relative to its molecular weight; protective value:
minimizes cellular T fluctuations
heat of vaporization – again high
solubility of ionic/polar compounds
solubility of organic compounds
determined by polarity/ability to form H-bonds
generalization – most organics with 5 or more carbons
are relatively insoluble in water
C. Non-covalent interactions in aqueous solution
relative magnitude
1. electrostatic interactions
ion-ion interactions
examples
salt
"salt bridges"
or ion pairing
ion-dipole interactions
examples salt in H20
2. hydrogen bonding
many possible pairings
small
van der Waals (short-range)
dipole-dipole
dipole-transient dipole
3. hydrophobic interactions
D. Acids and bases
pH calculations
strong acids
weak acids: incomplete dissociation
(Henderson-Hasselbach)
titration curves
buffers:
effective range of buffering by HA and A- is
from one unit above to one below pKa