Salt and Water

Water dissolves Salt

You'll need

  • a flat glass bowl
  • salt
  • semolina
  • a magnifying glass or a microscope

Experiment

  • Add water and a few grains of salt to the bowl and observe the salt crystals under the magnifying glass or microscope. The salt crystals will grow smaller and smaller, until they disappear completely.
  • Now conduct the same experiment with water and semolina. What do you see?

You'll need

  • glass of water
  • 1 spoon each of salt and semolina  
  • coffee filter
  • saucepan

Experiment

  • Add the salt and semolina to the water and stir until the salt has dissolved.
  • If you now wish to separate out this mixture of salt, water and semolina into its individual components, you must use different methods.
  • You can filter out the semolina by pouring the entire contents of the glass through a coffee filter: the semolina will be left clearly visible on the filter. Taste the water which has flown through the filter. Was the salt filtered out?
  • In order to get the salt out of the water, you will have to use a different separation method: Pour the salt solution into a saucepan and bring to a simmer on an electric range, long enough for the water to evaporate. All that remains in the pan is a white crust. What does the residue taste like?

3 + 1 = 3 ??

You'll need

  • pickle jar
  • salt
  • semolina

Experiment

  • Pour water into the pickle glass until about three-quarters full (ca. 0.5 liters) and mark the level.
  • Now add the salt, stir well until the salt has dissolved. Now check the water level.
  • In comparison, conduct the same test, this time with the same quantity of water and the same amount of semolina. What do you notice?

A grain of salt actually consists of many small particles which you can't see. If a grain of salt comes into contact with water, those individual particles break away from the larger grain of salt.

You have to imagine the water in this way: Between the individual water particles there are gaps. And the dissolved salt particles fit nicely into those gaps, which means the water level doesn't rise!