Electrolysis of brine; unexpected result

[Chap]

I electrolysed a brine solution using graphite electrodes. No attempt was made to minimize the chlorine (produced) reacting with the electrolytic solution. After a few hours, a white sludge (possibly Mg(OH)2 and Ca(OH)2) was formed, as expected. This was removed and the electrolysis was continued.

 

After a few hours, the graphite cathode started to flake off. The anode remained intact. This is surprising since I don't think hydrogen reacts with carbon under these experimental conditions. I initially thought maybe the Chlorate ion formed due to the dissolution of chlorine in the solution reacted with the graphite cathode, but that doesn't explain the fact that the anode remains intact.

 

Have I overlooked a simple fact?

[elementcollector1]

I electrolysed a brine solution using graphite electrodes. No attempt was made to minimize the chlorine (produced) reacting with the electrolytic solution. After a few hours, a white sludge (possibly Mg(OH)2 and Ca(OH)2) was formed, as expected. This was removed and the electrolysis was continued.

 

After a few hours, the graphite cathode started to flake off. The anode remained intact. This is surprising since I don't think hydrogen reacts with carbon under these experimental conditions. I initially thought maybe the Chlorate ion formed due to the dissolution of chlorine in the solution reacted with the graphite cathode, but that doesn't explain the fact that the anode remains intact.

 

Have I overlooked a simple fact?

 

Just to be sure, your anode was (+) and your cathode (-)?

With a graphite anode, when oxygen is produced in minute quantities it will actually react with the graphite to form a sort of intercalated 'graphite oxide', which will then weaken the overall structure.

This was seawater brine, right? Regular salt water would produce no precipitate.

[Chap]

yes, anode is (+) and the cathode is (-), I didn't make a mistake on the electrodes. Also, I don't think oxygen evolved at the anode (+) since the solution was almost saturated with NaCl. It is the cathode which eroded and not the anode. I did collect the gas that evolved from the anode and it is definitely chlorine gas (it had a slight yellow green color and pungent odor). I don't know whether it's possible for some oxygen to have evolved, but that's beside the point since it's not the anode which eroded, but the cathode. This is the puzzling question.

 

As for the brine solution that I am using, it is table salt brine not sea-water brine, but a slight precipitate still forms. I'm living in Sri Lanka (a developing nation), where salt is extracted from the sea. I'm not that aware of the exact refining process employed by our country, but maybe the table-salt in Sri Lanka s not as refined as table-slat in developed nations.