5.1 Physical Characteristics of Water

• Water has a high surface tension
• Surface tension is a result of cohesive force between the molecules of water at the surface that allows insects like daddy longlegs to stay afloat on water
• Cohesive force between water molecules and adhesive force between water molecules and the cell walls of xylem allow water to be drawn up from the roots to the leaves of plants. This phenomenon is known as capillary action
• During electrolysis, oxygen gas is produced at the anode while hydrogen gas is produced at the cathode
• A water molecule is made out of two hydrogen atoms and one oxygen atom
• Evaporation of water is the process that happens in the surface of water that changes water to water vapour. This process occurs at anytime.
• FACTORS AFFECTING RATE OF EVAPORATION

  • Humidity - Dry air contains less water vapour. So, dry air can hold more water melecules that escape from the surface of water. Thus, the rate of evaporation of water
• FACTORS AFFECTING RATE OF EVAPORATION

  • Surrounding temperature - When the surrounding temperature increases, the water molecules at the surface gain more energy, move faster and escape into the air easily. Thus, the rate of evaporation of water increases
• FACTORS AFFECTING RATE OF EVAPORATION

  • Exposed surface area of water - Exposed surface area of water that is larger allows more water molecules to escape, thus increasing the rate of evaporation of water.
• FACTORS AFFECTING RATE OF EVAPORATION

  • Movement of air - Movement of air sweeps away water vapour in the air. High speed of wind causes the air at the surface of water to dry and increases the rate of evaporation of water
• Applications of Evaporation of Water in Daily Life

  1. Clothes hung on clothes lines have large exposed surface areas. So, the clothes will dry faster
  2. Sea salt is obtained from the evaporation of seawater
  3. Seafood that is dried can be kept longer as microorganisms cannot survive without water
  4. Hair dryer that blows hot air increases the temperature, thus increasing evaporation of water
• Physical characteristics of Pure Water

  • Boiling point = 100
  • Freezing point= 0
  • Colourless
  • Density = 1 g cm3