Sodium in water
Some metals react with cold water, hot water and steam at widely different rates. Let us begin with sodium — the fastest of them.
Activity 16.4
- Into the water in a trough, drop a piece of red litmus and a small piece of sodium (Na), about the size of a green gram (with your teacher's assistance).
- Record your observations.
The observation
The piece of sodium darts about rapidly on the water making a hissing sound.
It grows smaller, and if it stays in one place it catches fire.
The red litmus in the trough turns blue.
What the two observations tell us
The sound and the movement
Sodium reacts rapidly with water, and in doing so hydrogen (H2) gas is given off.
The litmus turning blue
Red litmus turning blue shows that an alkaline solution has formed.
What happens here is that sodium reacts with cold water to form sodium hydroxide, an alkaline solution, and hydrogen.
2Na + 2H2O → 2NaOH + H2
Do not attempt this alone
Warning
The reaction of sodium with water gives out a great deal of heat and the hydrogen released can ignite. This activity must only ever be carried out under a teacher's supervision.