Obtainment of substance at the bottom layer by electrolysis, which reacts with water
name: Reduction of sodium from the solution on a mercury electrode
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.