Movie File Size - 4.7 MB Movie Duration - 98.92 Seconds File - MOVIES/NANH3/NANH3.mov (Click here for larger version of movie)

Discussion

When sodium metal is added to ammonia, some of the sodium dissolves. Each of the dissolving sodium atoms loses an electron and becomes a cation. Both the cation and the free electron are solvated by ammonia molecules.

Na(s) + (x+y) NH₃(l) → Na(NH₃)_x⁺(aq) + e^-(NH₃)_y(aq) (blue)

The blue color is characteristic of a solution containing solvated electrons; as the solution becomes more concentrated, it takes on a bronze color. The bubbles appearing as the reaction proceeds are hydrogen gas that is formed in a second reaction between the sodium and ammonia:

2 Na(s) + 2 NH₃(l) → 2 NaNH₂(aq) + H₂(g)

Narration

A small piece of sodium is cut to expose a fresh surface. The sodium is dropped into liquid ammonia at a temperature of approximately -33 degrees Celsius. Some of the sodium dissolves, forming sodium cations surrounded by ammonia molecules and electrons surrounded by ammonia molecules. The solvated electrons give the blue color to the solution. Because of the mobility of the electrons, the solution is a good electrical conductor. Bubbles of hydrogen gas are formed by a second reaction that also produces sodium amide. More concentrated solutions appear bronze-colored and have a conductivity similar to metals.