Chapter 2 – Water and pH
Water - one of the most important molecules in life.
70% of the bodies mass is water
2/3 of total body water is intracellular (55-66% body weight of men and 10% less for women)
The rest is interstitial fluid of which 25% is in the blood plasma.
pH - The body tightly controls both the volume and pH of water.
The bicarbonate system is crucial for blood maintenance
changes of pH greater than 0.1 are dangerous and can lead to coma -diabetics
Properties of water
Hydrogen bonding potential
Specific heat, heat of vaporization
Water is an ideal
Water is close to a tetrahedral shape with the unshared
electrons on the two sp
-hybridized orbital are in two corners and the
hydrogen in others
Compared to a tetrahedron, CH
) or NH
the bond angle is smaller
Water has hydrogen
•H-bonds are non-covalent, weak
O is both a Hydrogen donor and acceptor
O can form up to four H-bonds
What Are the Properties of Water?
A comparison of ice and water, in terms of H-bonds and Motion
Ice: 4 H bonds per water molecule
Water: 2.3 H bonds per water molecule
Ice: H-bond lifetime - about 10 microsec
Water: H-bond lifetime - about 10 psec
(10 psec = 0.00000000001 sec)
The Solvent Properties of Water Derive from Its Polar Nature
Water has a high dielectric constant
Ions are always hydrated in water and carry around a "hydration shell"
Water forms H bonds with polar solutes
The Solvent Properties of Water Derive
from Its Polar Nature
What makes this molecule important?
solvent ability - easily disrupts ionic compounds - dielectric constant (D) is
high (measure of the ability to keep ions apart)
Large electronegativity creates a strong ionic type
Liquid water has a higher density than solid water
(ice). Is this normal? Think of why this is important?
orderliness - solvating shells
ability to take place in many hydrogen bonds (up to
4 at a time)