Industrial Chemistry Question:
During the electrolysis of dilute NaCl, why is the water oxidised instead of the Chlorine ions? Because in the concentrated NaCl solution, the chlorine ions do get oxidised, however in the very dilute solution they do not. Just curious as to why this is.
Cheers.
Compare the E
o values of both oxidations:
2 Cl
- ⇌ Cl
2(g) + 2 e
- E
o=-1.36 V
2 H
2O
(l) ⇌ O
2(g) + 4 H
+ + 4 e
- E
o=-1.23 V
Notice how the two values are
very similar. This is opposed to the reduction, where the voltage required to cause sodium to reduce is significantly larger to water reducing.
Because the voltage is so similar, the EMF supplied will seek out the more abundant substance as about a similar amount of voltage is consumed anyway for either reaction. In concentrated sodium chloride solution, there is actually a sufficient amount of chloride ions for their oxidation to be favoured. In dilute solution, there really isn't that many, and water will be oxidised anyway.
Hey i was wondering if anyone has studied/currently studying shipwrecks that could help me understand the difference between a galvanic cell and an electrolytic cell, because I'm getting confused with the charge of the cathode and anode are.
Fortunately this overlaps into industrial chemistry.
Galvanic cells and electrolytic cells function
oppositely.
In a galvanic cell, a chemical reaction takes place producing a voltage, thereby chemical energy is converted to electrical energy
In an electrolytic cell, electricity is passed through a cell to reverse the effect of the galvanic cell, thereby electrical energy is converted to galvanic energy.
(The EMF value for a galvanic cell is positive, whereas that of an electrolytic cell is negative.)
Effectively, electrolytic cells can be used as battery rechargers.
The mnemonic RED-CAT AN-OX still takes play. Reduction happens at the cathode and oxidation happens at the anode.
However, the polarity reverses in an electrolytic cell.For a galvanic cell, the anode is negative and the cathode is positive.
Cathode: Cu
2+ + 2 e
- -> Cu
(s)Anode: Zn
(s) -> Zn
2+ + 2 e
-For an electrolytic cell, the anode is positive and the cathode is negative.
Cathode: Zn
2+ + 2 e
- -> Zn
(s)Anode: Cu
(s) -> Cu
2+ + 2 e
-Deleted last bit. Forgot the why. JAKE!