FOR EDUCATION PURPOSES ONLY

1. 5.1 PHYSICAL CHARACTERISTICS
OF WATER
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2. ABOUT WATER
 70% of the earth’s surface is
covered by water
 Exists as liquid at room temperature (20-22°C)
 Has a high surface tension
 Surface tension is a result of cohesive force between the molecules of water
at the surface allow insects like daddy longlegs to stay afloat on water
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3. CAPILLARY ACTION IN PLANT
Water molecules
Cell wall
Adhesive force between water
molecule and cell wall
Cohesive force between water
molecule
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 Allow water to be drawn up from roots to leaves of plants

4. PHYSICAL CHARACTERISTICS OF PURE
WATER
 Boiling point=100⁰C
 Freezing point=0⁰C
 Colourless
 Density=1g cm⁻3
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5. EFFECT OF ABSORPTION AND RELEASE
OF HEAT ON THE STATE OF WATER
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Sublimation
Sublimation
freezing Condensation
Evaporation/
Boiling
Melting

6. COMPOSITION OF WATER
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 Water is a compound; made up of oxygen and hydrogen
O
H
H
O
H
H
O
H
H
 The chemical symbol of water is H₂O

7. EFFECT OF IMPURITIES
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 The pot containing water boils faster than the one containing chicken soup
 Physical characteristic (taste, smell & colour) of water can change in
presence of impurities
 Example: Seawater tastes salty because it contains dissolved salt

8. EVAPORATION OF WATER
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Water vapour
 Evaporation happens at the surface of water
 The molecules of water at the surface have
higher kinetic energy, thus they can move
faster and escape into the air

9. FACTORS AFFECTING THE RATE OF
EVAPORATION OF WATER
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Humidity Dry air can hold more water molecules
that escape from the surface of water;
evaporation increases
Surrounding
temperature
When temperature increases, the water
molecules gain more energy, move faster
and escape into air easily; evaporation
increases
Exposed surface
area of water
Large exposed area of water allow water
molecules escape easily; evaporation
increases
Movement of air High speed of wind cause the air at the
surface of water to dry; evaporation
increases

10. APPLICATION OF EVAPORATION OF
WATER IN DAILY LIFE
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 Blow hot air increases the
temperature, thus increasing the
evaporation of water
 Hung clothes on the sunny day
 Dried fish; microorganisms
cannot survive without water