Question

What is produced at each electrode in the electrolysis of an aqueous solution of both NaBr and AgF ? Classify as Anode, Cathode, or Not Produced

1. Na(s)
2. F2(g)
3. Ag(s)
4. Br2(l)
5. O2(g)
6. H2(g)

I have tried these but 2 are wrong
1. Anode
2. Anode
3. Cathode
4. Cathode
5. Not Produced
6. Not Produced

Answer 1

In addition to the ions from AgF and NaBr, we must also consider the hydrogen and oxygen in water (I'm assuming this is aqueous solution).

If the solution is concentrated, we would expect to see only Ag at the cathode, and only Br2 at the anode. This can be seen from the reduction potentialsof the species involved. Br- is easier to oxidize than either O2- or F-, so it gets oxidized first. Ag+ is easier to reduce than either H+ or Na+, so Agmetal will come out first.

If the solution is more dilute (for example, after running for a while), the production of oxygen and hydrogen will become more favorable (thisfavorability depends upon the concentrations of the ions - see the link for the Nernst equation), and you will start to get some O2 at the anode and someH2 at the cathode (in addition to the Br2 and Ag).

F2 and Na will never be produced. F2 is such a powerful oxidizing agent that it will actually react with water to form HF and O2, so if any did happen toform, it would be consumed. Na, as you probably know, reacts violently with water, so if any Na metal formed, it would immediately be consumed by thewater.

NOTE: Actually, it just occurred to me: this might be a trick question. While AgF and NaBr are soluble, AgBr is not, and will precipitate if you actuallytry to form this solution. The only ions remaining (if you use equimolar amounts of NaBr and AgF) will be Na+ and F-, plus those from the water. Because F2and Na will not be formed, we will only see O2 at the anode and H2 at the cathode.