Manufacturing of Sodium Hydroxide|| Nelson's Cell|| Class 9|| Chemistry

On industrial scale caustic soda (sodium hydroxide) NaOH, is produced in Nelson's cell by the electrolysis of aqueous solution of NaCl called brine. The schematic diagram of the cell is shown in figure 7.5. It consists of a steel tank in which graphite anode is suspended in the center of a U shaped perforated iron cathode. This iron cathode is internally lined with asbestos diaphragm. Electrolyte brine is present inside the iron cathode. Aqueous solution of sodium chloride consists of Na , CI , H and OH ions. These ions move towards their respective electrodes and redox reactions take place at  these electrodes. When electrolysis takes place Cl ions are discharged at anode and CI 2 + gas rises into the dome at the top of the cell. The H ions are discharged at cathode and H 2 gas escapes through a pipe. The sodium hydroxide solution slowly percolates into a catch basin.