1.2 - Water: Life’s Solvent

• Cohesion: The attraction force between like molecules.

  • water molecules form hydrogen bonds with each other
• Adhesion: The attraction force between different molecules.

  • water molecules my form hydrogen bonds with other polar molecules
• Approximately 60% of your body is water.
• Properties of Water: Cohesion, Adhesion, High Specific Heat Capacity, High Specific Heat of Vaporization and Solid Water is Less Dense than Liquid Water.
• Water molecules are polar and have a strong attraction to each other.
• Hydrophilic: Polar substances that are attracted to water (ex. salt)
• Hydrophobic: Non-polar substances that are NOT attracted to water & non-soluble (ex. oil)
• Acids have a pH of less than 7 and are corrosive.
• Bases have a pH of 7<14. Acids have a pH of 0<7.
• A pH scale measures the concentration of hydrogen ions in a solution.
• Cohesive forces between molecules cause the surface of a liquid to contract to the smallest possible surface area —> creates surface tension
• What force allows plants to transport water (sticks to xylem)?


  Adhesion
• What force allows water to dissolve in polar substances?


  Adhesion
• What force allows insects to walk in water?

  Surface tension because of cohesion in water
• High Specific Heat Capacity - The ability of a substance to store and release heat energy.
• Why is High Specific Heat Capacity important?


  It helps organism to maintain a constant body temperature/heat.
• High Specific Heat of Vaporization - water absorbs large amounts of heat as it evaporates
• Why is High Specific Heat of Vaporization important?


  Helps organisms to cool themselves through evaporation (sweating )
• Why is solid water less dense than liquid water?

  Because as liquid water cools, a lattice structure is formed

  • molecules spread apart —> creates extra hydrogen bonds —> lowers density —> ice floats!
• Why is solid water useful?

  • Prevents ice from killing aquatic organisms
  • Snow keeps animals warm in winter—-> contains high insulation
• How can you tell is something is acidic?

  • Tastes sour
  • Conducts Electricity
  • Turns Blue Litmus paper Red
• How can you tell is something is basic?

  • Tastes Bitter
  • Feels Slippery
  • Conducts Electricity
  • Turns Red Litmus paper Blue
• Strong Acid/Base - completely dissociates in water
• Weak Acid/Base - only a small part of the molecule can dissociate in water
• Buffers - A chemical that can change pH by accepting or releasing H+ ions
• What does this buffer system do?

  Maintains blood pH to be stable

  
• Since most weak acids/weak bases have reversible reactions, they often act as buffers