Water Chemistry Lecture Notes

Importance of Water

• Essential for life on Earth
• Life would not exist without it

Chemistry of Water

Polar Molecule

• Water is a polar molecule with polar covalent bonds
• Capable of forming hydrogen bonds
• Forms hydrogen bonds between water molecules, not within

Properties Determined by Hydrogen Bonds

• Cohesion

  • Water molecules form hydrogen bonds with each other
  • Leads to properties like surface tension and capillary action

• Heat Storage

  • Hydrogen bonds, though weak, are additive and collectively strong
  • Water can absorb a lot of heat, moderating temperatures

• Solvent Ability

  • Dissolves ions or polar molecules by forming hydrogen bonds
  • Example: Water dissolves sodium chloride and proteins

Interaction with Nonpolar Molecules

• Water organizes nonpolar molecules (e.g., lipids, oils)
• Nonpolar molecules do not mix with water and are excluded from it
• Important for structures like plasma membranes

pH and Water

• pH Definition

  • Measure of hydrogen ion concentration in water
  • Inverse scale: low pH = high hydrogen ion concentration, high pH = low hydrogen ion concentration
  • Hydrogen ion = proton (interchangeable terms)

• Acids and Bases

  • Acids: Release hydrogen ions, increasing hydrogen ion concentration, lowering pH
  • Bases: Bind free hydrogen ions, reducing their concentration, increasing pH
  • Both impact pH, which affects biological processes