question_answer

  While eating food, you happen to spill some curry on your white shirt. You immediately scrub it with soap. What happens to its yellow colour on scrubbing with soap? Why? What happens to this stain when the shirt is washed with plenty of water?

Answer:

                  Crystals of some compounds seem to be dry (or anhydrous), but actually contain some water molecules attached to them. This water is called water of crystallisation and such salts are called hydrated salts.                                (1) The following activity shows that blue copper sulphate crystals contain water for crystallization Activity Heat a few copper sulphate crystals in a dry boiling tube. After sometime the blue colour of the crystals disappears and white powder of anhydrous copper sulphate is formed. A few drops of water also appear on the inner walls of the boiling tube. When some water is added to the boiling tube after heating, the blue colour reappears.