Water

(Review of what we already know)



Info we already know about water

  • Water is highly polar at the O-H covalent bonds
  • Because O is highly electronegative it attracts the electrons from the O-H bond making the O slightly negative and the H slightly positive.
  • The bond angle is 105 and has a bent shape and because of this shape the two polar ends do not cancel causing the whole molecule to be polar.
  • Polar molecules are attracted to each other by dipole interactions, but for water it’s molecular bonding is due to hydrogen bonding.

H- bonds and water

  • Most of waters unique properties result from it’s ability to hydrogen bond.
 

Surface Tension 

  • The surface tension of water acts like a skin.
  • The molecules within the liquid are surrounded by the hydrogen bonded to adjacent water molecules.
  • At the surface of the liquid the water molecules experience an uneven attraction and the water molecule is only hydrogen bonded to one side.
  • Since the water molecule cannot form a hydrogen bond with the air it is not attracted to the air so what ends up happening is the water molecules at the surface tend to be drawn into the body of the liquid.
  • The inward force or pull that tends to minimize the surface area of a liquid is called surface tension.
 

Affects of Detergents on Surface Tension

  • It is possible to decrease the surface tension of water by adding a substance like soap this is known as a surfactant.
  • What happens is the detergent molecules interface with the hydrogen bonding between water molecules and as a result the surface tension is reduced the beads collapse and the water spreads out.

vapor pressure

  • Water also has a very low vapor pressure because of hydrogen bonding.
  • Vapor pressure of a liquid is caused by molecules that escape the surface of the liquid and enter the gas phase.
  • Because hydrogen bonds hold water molecules to one another the tendency of these molecules to escape is low
  • if this didn’t happen all the lakes and oceans would evaporate rapidly because of their large surface areas.

Specific Heat (4.18 J/(goC)

  • The reason water has a high specific heat compared to most other objects is also due to hydrogen bonding.
  • Water helps control the climate due to its specific heat, on a hot day water absorbs the heat and on cold nights water releases the heat this is why water is a good medium for solar energy.
  • Unlike Iron which only has a specific heat of 0.447 J /(goC) so water can absorb about 10 times as much heat as iron.

complete the student response section