In an Electrolytic cell(voltameter)..

Electrolysis is defined as the decomposition of ionic compounds when electricity is passed through them in molten state or aqueous solutions.

How does this occur? This process is carried out in an electrolytic cell. It consists of two electrodes, metallic rod-shaped conductors which are dipped in a liquid electrolyte and connected by wire to the electron pumper, which in a typical setup is a dry cell or a battery. One of the electrode is an anode, which is connected to the positive terminal, the other, a cathode which is connected to the negative terminal of the battery. This makes the cathode negatively charged (as electrons flow from the negative to the positive terminal, in an opposite direction from conventional current flow), and the anode, positively charged. Since there is presence of ions, there are also cations and anions in an electrolytic cell. Positively-charged CATions are attracted to the negatively charged CAThode while negatively-charged ANions are attracted to the positively charged ANode. There is also a battery, to ensure that there is a difference in charge between the two ends of a conductor. This is to ensure a current can flow . It does so by converting chemical energy into electrical energy.

Redox reactions occur in an electrolytic cell, with reduction occuring at the cathode(electronegative), thus there is a gain of electrons at the cathode. Conversely, oxidation occurs at the anode(electropositive) and there is a loss of electrons at the anode.


(Below: Useful animation showing an electrolytic cell and electrolysis of Copper(II) Sulfate)
http://www.tutorvista.com/content/chemistry/chemistry-ii/electrolysis/electrolysis-animation.php