3.1.7 Water

3.1.7 Water

1. Molecular structure of water

   • 2x H and 1x O
   • Water is dipole
   • A polar molecule
     • Molecule contain a dipole
   • H bonding occurs due to dipole

2. Important properties of water

   • Liquid @ room temp
     • Provide stable habitat for organisms
     • Major component of tissues
     • Reaction medium
       • Reactants can move around in water
     • gr8 for transport
     • Due to H bonds
   • Density
     • water is most dense at 4℃
     • ∴ why ice can float on water as an insulating layer
   • Solvent
     • Things can dissolve in H₂O
     • reactions can occur more readily in water
       • allow for transport of solutes in water
     • AS water is dipole ionic molecules
       • ∴ water gets in-between the ionic molecules and dissolve them
   • Cohesion + surface tension
     • Ability of water molecules to 'stick' together
       • allow water to act as one column when being transported in plant vessels (Xylem)
     • Surface tension carries due to the interactions between H₂O molecules are greater than interaction w/ things surrounding it e.g Air
       • ∴ this allows water to support life at the water surface
   • Incompressibility
     • H₂O canto be squashed like a gas
     • ∴ cells can maintain their shape and size
   • High specific heat capacity + high latent heat of vaporisation
     • Need to put in 4.2KJ of energy to rise 1kg of water by 1℃
       • water ∴ doesn't quickly warm up or cool down
         • Stable temp = stable habitat
     • Requires a lot of energy to evaporate water
       • sweat cools the body quickly