Experiment:
Take a beaker and half fill it with water. Take a piece of sodium and cut a small wheat grain size piece from it. Press it first in a filter paper and then wrap it in cotton. Next, drop the piece in beaker. You will observe a violent reaction. Wait till the reaction stops completely. Now touch the beaker. Is it hot? Test the substafice in the beaker with red and blue litmus paper. You will see that the solution is basic due to the formation of sodium hydroxide. Sodium reacts violently with cold water.
