Sodium in water, formation of NaOH visualized
A simple, but nice experiment is adding sodium metal to water. The piece of sodium metal melts and skirts over the surface of the water, while producing hydrogen gas, and sodium hydroxide is going in solution.
The formation of sodium hydroxide can nicely be visualized when a few drops of solution of phenolphtalein is added to the water.
Performing the experiment is simple. Take a small piece of sodium metal and throw this in a glass tank, filled with water, to which a few drops of phenolphtalein solution are added. A good size for the tank is 2 liter.
The result of this experiment easily can be explained. The sodium reacts with water:
2Na + 2H2O → 2Na+ + 2OH– + H2 + heat
The hydroxide ions make the solution strongly alkaline. The phenolphtalein indicator turns pink/red at high pH. The higher density of the solution of NaOH causes the solution to sink to the bottom, giving rise to the nice patterns.
A video of this simple experiment can be downloaded: sodium skirting over water. Download size is approximately 2.6 MByte.