Help with Electrolysis: DC Power Supply & Cathode

[lwymarie]

bigKIDmarie* (下午 03:22) :

a passage from my chem textbk:
a d.c. power supply acts as an electron pump. if forces electrons from its negative pole to the cathode of the electrolytic cell. the cathode thus has excess electrons and becomes negatively charged.

does it mean that the d.c. power supply sends electrons to the cathode? but before the electrolyte starts decomposing, i.e. before it can conduct electricity, the circuit of d.c. supply + wire + graphite rod + electrolyte is not closed. So why is that the electrons can flow to the cathode?

 

[mrjeffy321]

One might be able to think of it as a capacitor.
In a capacitor, current does not flow through the capacitor, but yet, there is still a circuit while the capacitor is charging.

But in an electrolytic cell, the key is the electrolyte. When the electrolyte dissassociatate into ions when it is dissolved. These ions allow the flow of electrons through the water. So really, the circuit is closed when you first turn on the current.