Transcript Properties of water WJEC

Surface
Tension
Colour
Cohesion
Properties of Water
WJEC GCE BIOLOGY
Latent
heat
State at
room
temp.
Specific
heat
capacity
Density
Next
Properties of Water
WJEC GCE BIOLOGY
Match the property of water with
the corresponding significance
for life and correctly fill in the
table
START
Property of water
Ice is less dense than water
High surface tension
Strong cohesive properties and high
tensile strength
Colourless with a high transmission
Properties of Water
WJEC GCE BIOLOGY
Liquid at room temperature
In order to evaporate it must absorb a
large amount of energy (high latent
heat of vaporisation)
Water can absorb a lot of energy for
only a small rise in temperature (high
specific heat capacity)
Significance for life
Answers
The high surface tension of water
means that it can form a habitat on
the surface of the water
Can be used for cooling organisms
by evaporation of for example sweat
Ice forms an insulating layer over
water
Conditions are stable in cells and
aquatic environments
Can be used for transport and a
medium for reactions
Light can pass through cells for
photosynthesis
Water can be pulled through plants
in a column as the water molecules
are held together by H-bonds
Property of water
Ice is less dense than water
Ice forms an insulating layer over
water
High surface tension
The high surface tension of water
means that it can form a habitat on
the surface of the water
Properties of Water
Strong cohesive properties and high
tensile strength
WJEC GCE BIOLOGY
Significance for life
Water can be pulled through plants
in a column as the water molecules
are held together by H-bonds
Colourless with a high transmission
Light can pass through cells for
photosynthesis
Liquid at room temperature
Can be used for transport and a
medium for reactions
In order to evaporate it must absorb a
large amount of energy (high latent
heat of vaporisation)
Can be used for cooling organisms
by evaporation of for example sweat
Water can absorb a lot of energy for
only a small rise in temperature (high
specific heat capacity)
Conditions are stable in cells and
aquatic environments
Next
Properties of Water
WJEC GCE BIOLOGY
Surface Tension
• The surface of water can behave
like an elastic sheet
• The molecules in the bulk of the
liquid are effected by various
intermolecular forces of
attraction
• Those molecules in the surface
are not effected by molecules
above them, and therefore ‘pull’
together more strongly,
effectively resembling a
stretched membrane
• A habitat can therefore survive
on the surface of the water
Back
Colour – transmission of light
• Water is colourless and is
therefore transparent to light
• This means that sunlight can
reach the cells and pass through
them so that photosynthesis may
occur
Reflected by leaves
53%
10%
13%
Properties of Water
WJEC GCE BIOLOGY
Sun light
Light absorbed by leaves
(typical values):
Near IR 15%
Red 82%
Green 80%
Blue 84%
9%
8%
7%
7%
32%
Transmitted through
leaves
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Cohesion
• Water molecules show a strong
attraction to one another, this is
called cohesion.
Properties of Water
WJEC GCE BIOLOGY
Droplets of water
form spheres due to
cohesion between
water molecules
Back
Latent heat
•
While changing state, a substance will take
in heat energy (solid  liquid  gas), or
expel heat energy (gas  liquid  solid)
without a change in temperature. This is
termed Latent Heat.
temperature
evaporate
GAS
condense
Properties of Water
WJEC GCE BIOLOGY
•
melt
Water has a large latent heat
of vaporisation, and therefore
absorbs a large amount of
heat energy while changing
from water to vapour.
solidify
time
Back
State at room temperature
•
Water is a liquid at room temperature.
However, all other similar molecules
are gases.
+
H
O
H
Hydrogen bonds form
because of polar covalent
bonding between the oxygen
and hydrogen atoms
+
2-
Properties of Water
WJEC GCE BIOLOGY
+
H
O
H
+
+
H
O
H
+
2-
2-
+
H
O
2-
H
+
• Hydrogen bonds act
between the water
molecules, and they
attract them enough so
that it behaves as a liquid.
Back
Specific Heat Capacity
•
The heat needed to raise the
temperature of 1kg of water by 1°C is
termed the Specific Heat Capacity.
• Water has a large specific heat
capacity, and therefore can
absorb large amounts of heat
energy before its temperature
raises a significant amount.
Properties of Water
WJEC GCE BIOLOGY
thermometer
1kg of water
Back
Density of water
•
Unlike other substances, water
expands as it freezes.
H
Ice
Water
H
H
O
H
O
H
H
O
H
O
H
H
O
H
Properties of Water
H
H
H
Water molecules are able to
approach one another quite
closely
WJEC GCE BIOLOGY
O
H
H
O
H
O
O
Water molecules in ice form
a rigid structure so that there
is more space between
them, this is seen as
expansion as a whole
H
H
H
H
O
O
H
H
• As water expands when it
freezes, its density (mass per
unit volume) will decrease.
• This means that ice is less dense
than water, and will therefore
float on top of it.
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