Electrochemistry

A dry cell consists of a moist paste of \(\mathrm{NH}_4 \mathrm{Cl}\) and \(\mathrm{ZnCl}_2\) contained in a \(\mathrm{Zn}\) casing which encloses a Carbon rod surrounded by black \(\mathrm{MnO}_2\) paste. What is the role of \(\mathrm{ZnCl}_2\) in it?