The most active metals are the alkali metals. In order to prevent oxidizing, alkali metals are stored under petroleum or sealed in a glass ampoule in vacuum.
In this experiment, it was demonstrated how sodium reacts with water. Sodium is a soft metal and can easily be cut with a knife.
1) For the first experiment, a pea sized piece of sodium was cut and dropped into water.
An energetic reaction followed, yielding sodium hydroxide (NaOH) and hydrogen gas as reaction products:
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
or in ionic form:
2Na(s) + 2H2O(l) → 2Na+(aq) + 2OH–(aq) + H2(g)
In aqueous solutions, sodium hydroxide is dissociated into ions:
NaOH(aq) → Na+(aq) + OH–(aq), giving basic media
This was shown by indicator-phenolphthalein, in basic media phenolphthalein gives pink color.
2) In another version, the sodium is not thrown into water, but rather placed on a wet filter paper floating on water. The sodium on the wet paper starts to react with water below, releasing enough heat to first melt and then ignite. Sodium burns in air forming a mixture of sodium oxide (Na2O) and sodium peroxide (Na2O2):
4Na(s) + O2(g) → 2Na2O(s)
2Na(s) + O2(g) → Na2O2(s)
3) A larger piece of sodium, when dropped into water, usually creates an explosion.
Attention, this is a dangerous experiment. Whatever size the sodium piece is, it may still explode when in contact with water. Ethanol (C2H5OH) can be used for deactivating of sodium.