Water and Buffers Lecture 2

Importance of Water

• Comprises 70-90% of organisms, essential for nutrient dissolution and transportation.
• Facilitates chemical reactions in an aqueous environment.
• Critical for protein, nucleic acid, and membrane structure and function.

Structure of Water

• Composed of one oxygen atom and two hydrogen atoms.
• Oxygen has four electron pairs: two involved in covalent bonds with hydrogen, two as lone pairs.
• Water is a polar molecule, with opposite charges at each end.
• Electronegativity of oxygen creates a net dipole moment, enhancing hydrogen bonding capabilities.

Hydrogen Bonding

• Strong interactions occur between electronegative atoms (commonly nitrogen and oxygen).
• Hydrogen bonds are strongest when molecules are aligned linearly.
• Hydrogen can act as both a donor and acceptor, enabling extensive bonding (up to four per molecule).

Unique Properties of Water

• Exhibits remarkably high boiling and melting points due to hydrogen bonding.
• Demonstrates large surface tension resulting from cooperative hydrogen bonding.
• Hydrogen bonds are weaker than covalent bonds but accumulate to affect water's behavior significantly.

Water and Polar Solutes

• Water forms hydrogen bonds with polar substances, enhancing solubility.
• Polar solutes, including amino acids, small alcohols, and carbohydrates, replace water-water interactions with more favorable water-solute interactions.

Solubility Characteristics

• Hydrophilic substances dissolve readily in water due to favorable interactions.
• Hydrophobic substances poorly dissolve and tend to cluster, as they disrupt water-water interactions without forming significant water-solute interactions.

Ionization of Water

• Water can ionize into protons (H+) and hydroxide ions (OH–), a rapid reversible process.
• Most water molecules remain un-ionized, resulting in very low electrical conductivity.
• Water plays a role in biochemical processes including hydrolysis, condensation, and oxidation-reduction reactions.

Buffers and pH

• Buffers manage pH by minimizing changes in H+ concentration.
• Understanding dissociation constants of weak acids and bases is essential for comprehending buffering systems and pH scale.