Question

Sodium can be extracted by heating naturally occurring salt until it is molten. An electrochemical process is then used to extract the sodium. Cl2 is produced at the anode, and Na is collected at the cathode.

1. Write the half-reactions that occur at the anode and the cathode. Identify each as either oxidation or reduction. (4 points)

I have written the half-reactions as:
2Cl-(aq)---> Cl2 (g) + 2e- oxidation
Na+(aq) + e- ---> Na(s) reduction

2. Based on these half-reactions, write the correct potential levels.

I got that the potential level for Cl oxidizing was +1.36
And the potential level for Na reducing is -2.71

But I have also learned that the reduction half-reaction should have a more positive cell potential so I'm confused...did I do something wrong?

Answer 1

I don't know how you're defining the term potential level. The potential to oxidize Cl ion to Cl2 gas is -1.36 v and that for Na ion to Na metal is -2.71 v. The potential of the cell is -1.36 + (-2.71) = -4.07 v. Therefore, you need at least +4.07 v to electrolyzs molten NaCl. In practice you will need a larger voltage. I don't know why Na electrode should be higher; actually both should be a little higher due to the over voltage (also known as over potential) at the electrodes.

Answer 2

Why did you add the potentials rather than subtract?