Q.Explain the principle of electrolytic refining with an example.

Step 1 -- the principle. Electrolytic refining purifies a crude metal by electrolysis in a cell containing an aqueous solution of a salt of that same metal as electrolyte. Rods of the IMPURE metal form the anode, and thin strips of already-PURE metal form the cathode.

Step 2 -- what happens during electrolysis. On passing current, metal atoms at the anode are oxidised and dissolve into the electrolyte as metal ions; simultaneously, an equal amount of metal ion from the solution is reduced and deposits onto the cathode. Net effect: pure metal is transferred from the impure anode to the growing pure cathode, through the solution.

Step 3 -- what happens to impurities. Impurities in the anode that are LESS electropositive than the metal itself do not dissolve into solution; instead they simply detach and settle at the bottom of the cell as a sludge called anode mud (often valuable itself, as a source of precious-metal impurities). …

State the general anode/cathode/electrolyte setup for electrolytic refining and what happens at each electrode, then apply it t …

• Forgetting the fate of impurities -- students often describe the metal-transfer mechanism correctly but omit that LESS electropositive impurities settle out as anode mud rather than dissolving, which is …