Electrolytic preparation of sodium amalgam

Obtainment of substance at the bottom layer by electrolysis, which reacts with water

Scientific name: Reduction of sodium from the solution on a mercury electrode


Sodium Amalgam

by hkparker


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Reaction formula

2 NaCl → 2 Na(Hg) + Cl2

2 Na(Hg) + 2 H2O → 2 NaOH + H2 + Hg

Step-by-step instruction

  1. Pour 5 ml of mercury into a vial.
  2. Cover the graphite rod with wax. Its both ends must remain uncoated.
  3. Connect one end of the rod to the DC power supply to the negative terminal, using a crocodile.
  4. Lower the other end of the electrode into the mercury. The uncoated part should be completely lowered into mercury.
  5. Pour 10 ml of saturated sodium chloride solution above the mercury.
  6. Lower the second graphite electrode in sodium chloride solution so that it does not touch the mercury. Connect it to a DC power supply to the positive terminal, using a crocodile.
  7. Turn on the power. Pass electricity for several minutes.
  8. Observe the darkening of the top layer of mercury and the formation of bubbles.
  9. Take a small amount of the dark top layer of mercury and pour it into a beaker with distilled water, using a Pasteur pipette.
  10. Observe bubbling in the beaker with water.

Scientific background

It is known that sodium is a very active metal. So, electrolysis of water occurs on the cathode during the electrolysis of sodium salts solutions. The formation of even trace amounts of sodium metal is impossible because sodium rapidly reacts with water.

If mercury is used as the cathode, the sodium reducing process becomes possible. In fact in this case sodium amalgam is formed, which has a much lower activity. Thus, the rate of reaction between sodium and water is lower than the rate of formation of sodium amalgam. Therefore, there is the accumulation of sodium amalgam. Moreover, the reaction between sodium amalgam and water is heterogeneous and the reaction of the lower layers of the amalgam with water are much more difficult.

However, sodium amalgam, still reacts with water, as well as sodium metal, but much slower.


Published on 30 June 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst