Properties and Purification of Water | Learning Concepts | ORCHIDS
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Concept: Properties and Purification of Water

As we know, water is an important natural resource, and it possesses some unique properties, which are listed below.

Properties of water:

  • Pure water is colourless.
  • It does not have a characteristic smell and hence, is odourless.
  • It can dissolve many substances, making it an excellent solvent.
  • It is liquid at room temperature.
  • Water assumes the shape of the liquid in which it is poured.
  • It constitutes hydrogen and oxygen in a ratio of 2:1.
  • Water is a bad conductor of electricity i.e. it does not allow electricity to pass through it. Still, salts in it make water a good conductor of electricity.
  • Example: Tap water (which contains salts) is a good conductor of electricity, whereas distilled water (pure water) is a bad conductor.

States of water:

  • Water exists in all three states at different temperatures.
  • Water freezes and exists in the solid state at 0°C. The change of water from its liquid state to solid state is called solidification.
  • Water boils to form water vapour at 100°C.
  • Ice starts melting at the temperature of 4°C.

Soluble and insoluble substances:

  • The substances that dissolve in water are called soluble substances.
  • Soluble substances can be either solid, liquid or gas.
  • The substances that do not dissolve in water are called insoluble substances.
  • The method of purification of water depends on the type of impurities present in it.
  • Soluble impurities are separated using different methods, while insoluble impurities require other purification techniques.

Methods of purification of water:

  1. Evaporation:
    • The conversion of the liquid state of water into its gaseous state is called evaporation.
    • This method is used to separate soluble impurities like salt or sugar.
    • Water containing the soluble impurities is heated.
    • Meanwhile, the water evaporates, collected separately, whereas impurities like salt or sugar are left behind as the residue.
  2. Sedimentation and Decantation:
    • This method is used for removing insoluble impurities like mud and clay particles.
    • The water is taken in a container and left undisturbed for a while.
    • As a result, the clay and mud particles gradually settle down.
    • The clear water from the top is then poured into another vessel, and this method is called decantation.
    • Alum, a transparent rock-like substance, is used to increase the rate of sedimentation.
    • Dissolving a tiny amount of alum in water increases the weight of the insoluble impurities, which allows them to settle down rapidly.
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  3. Distillation:
    • This method is used to separate water from liquid impurities like oil or alcohol.
    • During this process, water is heated up to its boiling point. Water evaporates, leaving behind the impurities.
    • The evaporated water vapour is then collected in a condenser, where it condenses to form distilled water.
  4. Filtration:
    • This method is used to separate insoluble impurities from water by using a strainer, muslin cloth or filter paper.
    • The impure water is passed through the above-mentioned things. The impurities accumulate on the strainer, muslin cloth or filter paper while the clear water gets filtered out.
    • Impurities like cereals, husk, sand, etc., can be separated by this method.

Water treatment plant

  • A water treatment plant is a facility for large scale purification of water.
  • The setup consists of various complex machines.
  • Water treatment plants are usually built to purify water before it is distributed to the different households in the urban areas.
  • These plants also help reduce the impurity levels of industrial wastewater before it is released into nearby waterbodies.
  • Water is also recycled in these treatment plants.
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Steps involved in the purification of water in a water treatment plant:

  1. Primary treatment:
    • This step involves filtering and removing large insoluble waste like plastics, wrappers etc.
    • The water is then allowed to flow through a screen which does not allow the solid waste to flow ahead.
    • Then the separated water is transported to the sedimentation chamber.
  2. Secondary Treatment:
    • The biodegradable solid waste is allowed to digest by the use of bacteria.
    • The bacteria consume the waste matter, which makes the water clearer.
    • The water is then left in the sedimentation tank for a while so that the remaining impurities settle down.
  3. Disinfection of water:
    • The water obtained after the tertiary treatment is treated with chlorine and UV rays is passed through the water which kills the harmful bacteria present.
    • This water is then supplied to houses where it is used again and sent back to the water treatment plant through sewage channels.
    • In the case of industries, the wastewater, which is released as a result of several chemical processes, is first treated to remove the hazardous chemical substances present in it and then released into the nearby water bodies.
    • Such treatment of wastewater is done to reduce the water pollution level.
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Judicious use of water:

Implementation of the following habits in daily life would help control the overuse and wastage of water.

  • We should turn off the tap while brushing our teeth.
  • Buckets should be used instead of showers for bathing.
  • Plants should be watered early morning or evening so that the water stays in the soil rather than evaporating quickly.
  • Water should be reused whenever possible, like the water used for washing vegetables can be used for mopping the floor.
  • Leaks in the pipes should be repaired immediately to prevent further water wasting.
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New Words

Room temperature: In this case, it denotes the temperature of 25°C. In general, room temperature means a range of temperature comfortable to human beings.

Hazardous: Something which is toxic and can cause harm.

Sedimentation: The settling down of heavier particles at the bottom of the container.

Did You Know?

  • The Bahr El-Baqar wastewater treatment plant is the world’s largest water treatment plant located in Egypt.
  • The water that comes from the kitchen, laundries and domestic baths is called grey water, whereas the water that comprises animal, food or human waste is called black water.
  • The waste which is removed during sedimentation after bacterial treatment is often used as organic fertiliser.
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