How does ammonia react with sodium

Experiment 32: Dissolving sodium in liquid ammonia

Experiment 32: Dissolving sodium in liquid ammonia

Equipment:
  • Tripod material
  • Round bottom flask
  • Glass stopper
  • Cutting board
  • knife
  • tweezers
  • Protective gloves
  • safety goggles
Chemicals:
  • Liquid ammonia (see notes)
  • sodium
Hazard warnings:
  • Ammonia (liquid): toxic, corrosive, dangerous for the environment
  • Sodium: corrosive, flammable
Attention! Do not breathe ammonia vapors. Work under the hood! Wear protective gloves when working with sodium.
Execution:
A round bottom flask filled with liquid ammonia is removed from the Dewar and attached to the stand. The glass stopper is lifted and a piece of debarked sodium is thrown in with tweezers.


Fig. 3521 Sketch "Sodium in liquid ammonia" (SVG)
observation
The sodium dissolves in the ammonia with a deep blue color.
Explanation:
Liquid ammonia is a great solvent. Alkali or alkaline earth metals dissolve in ammonia without hydrogen evolution with a blue color. These solutions can be kept for a long time and are powerful reducing agents. The metal-ammonia solution contains solvated metal cations and electrons, in the case of sodium that is and . The deep blue color comes from the solvated electrons - these are also responsible for great electrical conductivity and paramagnetism. Paramagnetism occurs when a substance contains unpaired electrons: the paramagnetic substance is attracted by a magnetic field, as these unpaired electrons now align themselves with the magnetic field. However, when the metal concentration increases, the paramagnetism decreases because the solvated electrons in the solution pair. It then lies before, the solution becomes diamagnetic.
Reaction equation:
Disposal:
Allow the contents of the flask to evaporate in a Petri dish under the hood. The solid residues are dissolved in ethanol, neutralized and disposed of at the local authority.
Remarks:
Ammonia gas produced from ammonium chloride and potassium hydroxide can be liquefied in a cold trap at -78 ° C over an isopropanol-dry ice mixture. More precise instructions can be found in the relevant literature (Lagowski, JJ (1978). "The Chemistry of Liquid Ammonia." Journal of Chemical Education 55 (12): 752-761) (Maslowsky, EJ (2000). "Microscale Synthesis of Hexaamminechromium." (III) Nitrate Using Liquid Ammonia Generated in the Laboratory. "Journal of Chemical Education 77 (6): 760-761)