• Water is not an organic molecule but is essential
for life on this planet
• All cells are surrounded inside and out with water
– anything that interacts with a cell must first be
dissolved in water
• Physical properties:
–
–
–
–
colourless and transparent
liquid at room temperature
density = 1.0 g/mL
m.p. = 0℃
b.p = 100℃
• water has LD, D-D forces, and H-bonding
• Water has cohesive properties – the high
number of intermolecular forces causes water
molecules to ‘stick’ together
Examples:
– surface tension – beading of water
– water striders – too light to break surface tension
– transpiration in plants – transport in xylem tubes
• Water has adhesive properties – it’s polar
nature causes it to stick to other substances
Examples:
– capillary action – water ‘climbs’ up small diameter
tubes, or ‘bleeds’ through the microscopic pores
and channels in paper or other porous substances
– this is due to the hydrogen bonding interactions
between the water and the surface of the tube
(either SiO2 or the cellulose tubes of paper)
– This helps to explain the meniscus inside a tube
• Water has outstanding solvent properties
• Used to be called the ‘universal solvent’, but this is not a good
name, since not everything dissolves in water
• The polar nature of water allows any other polar substance or
any charged particle to dissolve easily
• The δ- will attract the δ+ end of solutes, and this attraction will
remain once the solute is dissolved.
• The same is true for ionic substances – the cation will be
attracted to the δ- end of water, and the anion will be
attracted to the δ+ of water.
• Water has a high specific heat capacity
• This is a measure of the amount of heat energy required to
increase the temperature of a 1g of a substance by 1℃.
• cwater = 4.18 J/g‧℃
• This is high compared to other substances:
ccopper = 0.385 J/g‧℃
cglass = 0.735 J/g‧℃
cair = 1.00 J/g‧℃
ciron = 0.450 J/g‧℃
• A metal pan absorbs heat energy quickly and loses it quickly.
This makes metals useful for cooking.
• Water takes more energy to heat up – thus the time it takes to
boil water in a pot.
• Moderation of climate
• This property of water also helps to moderate
temperature changes in cells
Special Properties of water
• Water has a high latent heat of vaporization
and fusion.
• Latent heat is the energy absorbed or released
by a substance during a change of state.
• Lf water = 334 J/g
• Lv water = 2260 J/g
Latent heat
Latent heat of vaporization
• Evaporative cooling relies on Lv of water.
Latent heat of fusion
• Tender fruit farmers take advantage of the
latent heat of fusion of ice when there is a
chance of frost
• On an evening when there is frost in the
forecast, they spray water over their fruit,
causing ice to form as the temperature drops
below 0°C.
• How does this help to protect
the fruit?
Special Properties of water
• Water’s density decreases as it changes from liquid to
solid.
• This is because the distance between molecules in a
crystal lattice (as ice) on average further than when in a
liquid.
HOMEWORK
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Read and Summarize
Page: 195 “Salt and Ice”
Pages: 196-197 Unuaual Properties of Water
Questions page 198 # 1,11