Castner-kellner process chemical equations reactions at electrodes
Answers
Answer:
The apparatus shown is divided into two types of cells separated by slate walls. The first type, shown on the right and left of the diagram, uses an electrolyte of sodium chloride solution, a graphite anode (A), and a mercury cathode (M). The other type of cell, shown in the center of the diagram, uses an electrolyte of sodium hydroxide solution, a mercury anode (M), and an iron cathode (D). The mercury electrode is common between the two cells. This is achieved by having the walls separating the cells dip below the level of the electrolytes but still allow the mercury to flow beneath them.
Explanation:
The reaction at anode (A) is:
Cl− →1/2 Cl2 + e−
The chlorine gas that results vents at the top of the outside cells where it is collected as a byproduct of the process. The reaction at the mercury cathode in the outer cells is
Na+ + e− → Na (amalgam)
The sodium metal formed by this reaction dissolves in the mercury to form an amalgam. The mercury conducts the current from the outside cells to the center cell. In addition, a rocking mechanism (B shown by fulcrum on the left and rotating eccentric on the right) agitates the mercury to transport the dissolved sodium metal from the outside cells to the center cell.
The anode reaction in the center cell takes place at the interface between the mercury and the sodium hydroxide solution.
2Na (amalgam) → 2Na+ + 2e−
Finally at the iron cathode (D) of the center cell the reaction is
2H2O + 2e− → 2OH− + H2
The net effect is that the concentration of sodium chloride in the outside cells decreases and the concentration of sodium hydroxide in the center cell increases. As the process continues, some sodium hydroxide solution is withdrawn from center cell as output product and is replaced with water. Sodium chloride is added to the outside cells to replace what has been electrolyzed.
Explanation:
On industrial scale sodium hydroxide can be prepared by the following methods. In castner-kellner method NaOH is prepared by the electrolysis of aqueous solution of NaCl(Brine). i.e. 25 gm of NaCl is dissolved in 75 gm of water. Flowing layer of mercury (Hg) at the bottom of tank serves as cathode.