Biochemistry Quiz on Water Properties

Study Notes

Water is the most abundant substance in living organisms, comprising 70% or more of their weight
Early life likely originated in an aqueous environment
Water's properties (e.g., attractive forces, ionization tendencies) deeply affect biomolecules' structure and function
Water molecules are polar, enabling them to form hydrogen bonds with each other and solutes
Hydrogen bonds are relatively weak (23 kJ/mol) compared to covalent bonds (470 kJ/mol) but still very influential
Hydrogen bonding leads to water's high melting point, boiling point and heat of vaporization compared to other solvents
Water molecules cluster together in ice forming a crystal lattice, causing ice to be less dense than liquid water
Water dissolves salts (e.g., NaCl) by hydrating ions, weakening electrostatic attraction and making them soluble
The dielectric constant of water (78.5 at 25°C) screens electrostatic interactions between dissolved ions
Nonpolar molecules cluster together in water
Water's ability to form hydrogen bonds with itself and solutes influences solute solubility
The ordering (reduced entropy) of water surrounding nonpolar solutes is energetically unfavorable

Hydrogen bonds between water molecules provide cohesive forces, making water a liquid at room temperature
Water's unique properties are crucial to life
Weak interactions (hydrogen bonds, ionic, hydrophobic, and van der Waals) determine the three-dimensional structures of biological molecules (e.g., proteins, nucleic acids)
These weak interactions collectively significantly influence biological molecules' structures contributing to their strength, flexibility and precise shapes
Water's ability to form hydrogen bonds with polar solutes facilitates the solubility of polar biomolecules
The strength of hydrogen bonds is determined by the orientation of the molecules, maximizing electrostatic attraction when the molecules are in line

Water ionizes slightly into H⁺ and OH⁻ ions.
The ionization of water is an equilibrium reaction expressed by a constant (K)
Water's ionization is significant because it contributes to the pH of solutions.
Weak acids and bases also ionize in water, influencing the pH.
Equilibrium constants describe the proportion of reactants compared to products in an equilibrium reaction
Equilibrium constants can be calculated from the concentrations of reactants and products at equilibrium,
The ionization of water is expressed by an equilibrium constant (K)
The product of [H⁺] and [OH⁻] in water is called K_w, which has a constant value at a given temperature
The pH scale measures hydrogen ion concentration
Changes in pH can affect the structure and function of biomolecules.