Electrolysis of brine & half eqs

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#1
For the electrolysis of brine, the 2 half equations are;

2Cl = Cl2 + 2e
2H+ + 2e = H2

In a past paper I did, the mark scheme said the Cl half eq occurs at the anode and the H eq occurs at the cathode. Surely it should be the other way round because Cl is a negative ion and H is positive? Wouldn't they be attracted to the anode/cathode with the opposite charge to the ion?
If anyone could tell me why the half equations are like this that would be really helpful
1
2 years ago
#2
(Original post by larissa67)
For the electrolysis of brine, the 2 half equations are;

2Cl = Cl2 + 2e
2H+ + 2e = H2

In a past paper I did, the mark scheme said the Cl half eq occurs at the anode and the H eq occurs at the cathode. Surely it should be the other way round because Cl is a negative ion and H is positive? Wouldn't they be attracted to the anode/cathode with the opposite charge to the ion?
If anyone could tell me why the half equations are like this that would be really helpful
Anions go to the anode- the anode is the electrode that oxidation occurs on
and vv of course
0
2 years ago
#3
The Chloride is an ion because it has gained electrons.
In order for it to become pure chlorine it has to lose those electrons, hence the 2Cl- + 2e- --> Cl2
The chlorine is a negative ion, that's called an anion in chemistry. The anode is the electrode which is positive.
Therefore, the anions go to the anode and vice versa for the Hydrogen.
But because it's an aqueous solution, it's different than molten electrolysis.

Feel free to message me if you need more help
0
2 years ago
#4
(Original post by RetroKnight)
The Chlorine is an ion because it has gained electrons.
In order for it to become pure chlorine it has to lose those electrons, hence the Cl2 -> 2Cl- + 2e
The chlorine is a negative ion, that's called an anion in chemistry. The anode is the electrode which is positive.
Therefore, the anions go to the anode and vice versa for the Hydrogen.
But because it's an aqueous solution, it's different than molten electrolysis.

Feel free to message me if you need more help
chloride is an ion, not chlorine
your half equation is also incorrect, you're starting with Cl- and producing Cl2
0
#5
(Original post by Poooky)
Anions go to the anode- the anode is the electrode that oxidation occurs on
and vv of course
Ahhh okay obviously! Thank you
0
#6
(Original post by Poooky)
chloride is an ion, not chlorine
your half equation is also incorrect, you're starting with Cl- and producing Cl2
Ooh I forgot that and anION is negative but the anODE is positive - they get swapped around (why does everything in chemistry have to be complicated???!!), thanks for clearing that up!! Thank you
0
2 years ago
#7
(Original post by larissa67)
Ooh I forgot that and anION is negative but the anODE is positive - they get swapped around (why does everything in chemistry have to be complicated???!!), thanks for clearing that up!! Thank you
it's easier just to remember anions go to the anode (not true in fuels cells though, which is why I said anode is oxidation at the top!)
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