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Chapter 9 Water

Point to note:

  • Water is a universal solvent as it dissolves most things

Properties of Water:

  1. Freezing point of pure water is 0 degrees and boiling point is 100 degrees celcius

  2. Water expands as it freezes

  3. The density of water is 1g/cm3 but the density of its solid is .98g/cm3. Therefore the solid is less dense than the liquid

  4. Water is an excellent solvent

  5. There are two main tests for the presence of water:

   (i) Anhydrous copper sulfate when water is added turns blue

   (ii) Water turns blue cobalt chloride paper pink

   6. Water tends to cling to glass as the particles are more attracted to glass than they are to one another.              This forms a curved line called the meniscus.

Left: Water is unusual in that it turns litmus paper pink
 
Right: The curve at the top is known as the meniscus. When dealing with it in chemistry you must measure the lowest level of the meniscus
Water Cycle:

  • The continual re-circulation of water is called the water cycle-There are several stages to the water cycle:

 

  1. Evaporation: The energy (heat) from the sun makes the water in the oceans, seas and lakes evaporate i.e change from water to water vapour. This now begins to rise

  2. Condensation: As the water vapour rises it begins to coo, and condense into water droplets which are contained in clouds

  3. Precipitation: As the clouds cannot hold the water droplets it releases it as rain (snow, sleet or hail if cold)

  4. Run off: The water then through the streams and rock return to the sea and the cycle begins again 

Water Treatment:

  • There are many different stages to water treatment:

 

  1. Screening: The water passes through a wire mesh. This removes any debris e.g plastic bags from the water

  2. Settling: Water now flows into sedmentation tanks. Aluminium sulfate is now added to the water  to remove the small suspended particles that make water cloudy. The water will now be clear

  3. Filtration: The water now passes through beds of sand and ground. Removing even the smallest particles of debris do not stay in the water

  4. Chlorination: In this step chlorine is added to the water but only a very small amount. This acts as a disinfection removing any germs from the water

  5. Fluridation: In this step sodium fluoride is added to the water. This is to prevent tooth decay as fluoride is found in most toothpastes

The Water Cycle
Steps in Water Treatment

© 2016 by Vincent Savage and John Harrington. Young Scientists and Historians

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