What to ExpectA small piece of sodium metal will be placed in a bowl of water. If phenolphthalein indicator has been added to the water, the sodium will leave a pink trail behind it as the metal sputters and reacts. The reaction is:
2 Na + 2 H2O → 2 Na+ + 2 OH- + H2(g)
The reaction is especially vigorous when warm water is used. The reaction may spray out molten sodium metal and the hydrogen gas may ignite so it is imperative that proper safety precautions be used when conducting this demonstration.
- Never use a piece of sodium larger than a pea or pencil eraser.
- Safety goggles should be worn.
- The reaction should be carried out behind a clear safety barrier or at a distance from the students.
Materials for the Sodium in Water Demo
- sodium metal stored under mineral oil
- 250 ml beaker, filled halfway with water
- phenolphthalein (optional)
Sodium in Water Demo Procedure
- Add a few drops of phenophthalein indicator to the water in the beaker. (optional)
- You may wish to place the beaker on an overhead projector screen, which will give you a way to show the reaction to students from a distance.
- While wearing gloves, use a dry spatula to remove a very small chunk (0.1 cm3) of sodium metal from the piece stored in the oil. Return the unused sodium to the oil and seal the container. You can use tongs or tweezers to dry the small piece of metal on a paper towel. You may wish to allow the students to examine the cut surface of the sodium. Instruct the students that they can look at the sample, but must not touch the sodium metal.
- Drop the piece of sodium into the water. Immediately stand back! As water dissociates into H+ and OH-, hydrogen gas will be evolved. The increasing concentration of OH- ions in the solution will raise its pH and cause the liquid to turn pink.
- After the sodium has reacted completely, you can flush it with water and rinse it down the drain. Continue to wear eye protection when disposing of the reaction, just in case a bit of unreacted sodium remained.