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Three solutions are electrolysed between platinum electrodes…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Three solutions are electrolysed between platinum electrodes. Use for water at the cathode and for water at the anode. The couples are: at , at , at , at and at . Sulphate is not oxidised. Find the least voltage that starts the electrolysis of aqueous sodium chloride, silver sulphate and aluminium iodide.
Need a reminder? The key ideaShow
In an electrolytic cell the anode is joined to the positive terminal of the battery and oxidation happens there. The cathode is negative and reduction happens there. At the cathode the species with the higher reduction potential is reduced, and water is a rival at . At the anode the species with the lower potential is oxidised, and water is a rival at about . An active electrode can dissolve.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Find the winner at each electrode, then subtract.
Step 1. Sodium chloride. Cathode: water, , beats sodium. Anode: chloride, , beats water. .
Step 2. Silver sulphate. Cathode: silver, . Anode: sulphate is not oxidised, so water, . .
Step 3. Aluminium iodide. Cathode: aluminium, , is far below water's , so water is reduced. Anode: iodide, . .
Answer: , and .
Check. All three are positive and of the size of a battery or two. Real cells need more than this, because of the resistance of the solution.
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