Electrode gains mass....F325 question.

In a f325 question that I did today it said that the chromium electrode gains 1.456g in mass, does a gain in mass at the chromium electrode mean that chromium has been reduced (and gained electrons)

Does the gain in mass correspond to electrons being gained........i would have thought that the mass of electrons being added was negligible?

Reply 1

samb1234

13

No, almost certainly there is some metal ion in solution which is gaining electrons so for example if there were Cu2+ ions they would be gaining 2 electrons and you would get solid Cu deposits on the electrode

Reply 2

Chloe.B

OP

2

Sorry to be annoying, I still don't understand :frown:

Reply 3

Chloe.B

OP

2

So by cu2+ gaining two electrons, its mass will be increase as it is been reduced? Is that understand correct

Reply 4

samb1234

13

Original post by Chloe.B

So by cu2+ gaining two electrons, its mass will be increase as it is been reduced? Is that understand correct

No (well technically yes, but a single electron has a mass 1/1836th that of a proton which is negligible). So normally with electrolysis you would have a +ve electrode, with a lack of electrons, and a negative electrode, which has excess electrons, placed in a solution of an ionic substance, so using the example of cuso4 you would have Cu2+ and SO4 2- ions in the solution. The positive Cu2+ ions are attracted to the negative electrode. When they reach the negative electrode, the Cu2+ ions gain 2 electrons and are reduced to Cu, which is insoluble, so you get a layer of Copper metal on the electrode itself. Therefore the mass of the electrode increases, as you now have both the original mass of the electrode as well as the mass of the solid copper deposited on it.

Reply 5

Aubrey_79

11

Original post by Chloe.B

So by cu2+ gaining two electrons, its mass will be increase as it is been reduced? Is that understand correct

Hi,

Go on to Youtube and search MaChemGuy.
He goes over Electrode Potential and all A2 topics really well.

Reply 6

Chloe.B

OP

2

Thank you very much for your detailed response. Really appreciate it.

Original post by samb1234

No (well technically yes, but a single electron has a mass 1/1836th that of a proton which is negligible). So normally with electrolysis you would have a +ve electrode, with a lack of electrons, and a negative electrode, which has excess electrons, placed in a solution of an ionic substance, so using the example of cuso4 you would have Cu2+ and SO4 2- ions in the solution. The positive Cu2+ ions are attracted to the negative electrode. When they reach the negative electrode, the Cu2+ ions gain 2 electrons and are reduced to Cu, which is insoluble, so you get a layer of Copper metal on the electrode itself. Therefore the mass of the electrode increases, as you now have both the original mass of the electrode as well as the mass of the solid copper deposited on it.