Chemical Concepts Demonstrated: Ammonia chemistry, ammoniacal solutions, solvated electron chemistry
|Dissolve a sodium metal chip into liquid ammonia.|
A blue-colored solution forms.
Explanations (including important chemical equations):
Sodium metal is all too happy to donate an electron in most circumstances. This case is no exception, although the location to which the electron is donated is a little unusual.
Ammonia's liquid lattice has a recurring gap with a radius of about 3.3 Angstroms. Through a fortunate orientation of the dipole moments within the lattice, this space can actually accomodate an electron. Sodium donates the electron to the gap, even though the electron doesn't bond to the ammonia. In this manner, sodium (or another active metal, such as Na, K, Ba, or Ca) can donate an electron and liquid ammomia doesn't have to pick it up. This leaves an uncoupled electron in solution, the solvated electron.
The solvated electron gives solutions such as these a blue color and the conductivity of an aqueous solution of an inorganic salt. If it were concentrated, it would have a bronze color and conduct electricity like a full-blown metal.
Eventually, this solution will lose H2 to form sodium amide:
2 Na (s) + 2 NH3 (l) --> 2 NaNH2 (s) + H2 (g)