CHE 476 Chapter 2

Water

Ionic (Coulombic) Interactions

Electrostatic interactions between permanently charged species or between an ion and a permanent dipole.

Dipole Interactions

Electrostatic interactions between uncharged but polar molecules.

van der Waals Interactions

Weak interactions between all atoms, regardless of polarity. Include attractive (dispersion) and repulsive (steric) components.

Hydrophobic Effect

The phenomenon where nonpolar molecules aggregate in aqueous solutions to minimize the ordering of water molecules around them. Leads to decreased entropy of the system.

Protections from UV Light

Life evolved in water as it provides protection from harmful UV radiation.

High Water Content

Organisms typically contain 70-90% water, essential for biochemical reactions.

Solvent Properties

Water is a versatile solvent, dissolving a wide range of substances, facilitating chemical reactions.

Role in Structure and Function

Water influences the structure and function of proteins, nucleic acids, and membranes.

Entropy Considerations

The aggregation reduces the surface area exposed to water, decreasing the number of ordered water molecules and increasing the systems entropy.

Solubility

Nonpolar solutes have low solubility in water due to the hydrophobic effect.

Osmotic Pressure

Is affected by dissolved solutes, driving water movement across membranes.

Proton Hydration

Protons in solution form hydronium ions (H3O+), which are solvated by nearby water molecules, facilitating proton hopping.

Ionization of Water

Water can ionize into H+ and OH- ions, though the count of ionization is low (low Keq).

Weak Acids and Bases

They partially ionize in water, establishing an equilibrium between the ionized and unionized forms.

Buffers

Solutions that resist changes in pH upon the addition of small amounts of acid or base. They consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

Buffer Action

Buffers stabilize pH by neutralizing added acids or bases. This is crucial for maintaining the optimal pH range for enzymatic and biochemical processes.

Biological Importance of Buffers

Essential in biological systems to maintain homeostasis and proper functioning of metabolic pathways.

Hydrolysis Reactions

Water molecules break down larger molecules into smaller units.

Dehydration Synthesis

Water is released when smaller molecules combine to form larger moleculres.

Enzyme Function

Water is essential for the proper functioning of enzymes, often acting as a reactant or product in enzymatic reactions.

Molecular Geometry

Water has a distorted tetrahedral geometry with a dipole moment, making it both a hydrogen bond donor and acceptor.

Ice Structure

Hexagonal ice is the most common form, with maximal hydrogen bonding and lower density than liquid water, causing it to float.