Question

The Zinc rod in leclanche cell is coated with a thin layer of mercury because

• A. The defect of polarization is removed.
• B. The defect of local action is removed.
• C. The cell does not remain dirty.
• D. The cell is brightened.

Answer 1

The correct option is B The defect of local action is removed.

Local Action is the tendency for the chemically active components of a cell to react with each other, and so become exhausted even when no current is being drawn from the cell. Local action has the effect of reducing the 'shelf-life' of the cell - it uses up its chemical reserves and becomes exhausted even when not being used.

In a cell formed from zinc and copper electrodes suspended in a weak acid solution, local action can be seen. The zinc becomes coated with hydrogen bubbles, as a result of its reacting with the acid, even when no current is being drawn. After a while either the zinc will be entirely consumed, or the acid will be neutralised. To avoid this, a thin layer of mercury is coated on zinc rod.