CBSE Class 10 Science 2020 · Paper 31/5/1 · Question 25(b)

(a) Electrolytic refining of copper (labelled diagram as shown): the anode is a thick block of impure copper, joined to the positive terminal; the cathode is a thin strip of pure copper, joined to the negative terminal; the electrolyte is acidified copper sulphate solution. On passing the current, copper from the impure anode dissolves into the electrolyte, and an equivalent amount of pure copper is deposited on the cathode. Soluble impurities go into the solution, and insoluble impurities settle below the anode as anode mud. (b) The gap between the broken ends is filled with molten iron, formed by the reaction of iron(III) oxide with aluminium powder. The process is the thermit process (thermit reaction): ${\text{Fe}}_2{\text{O}}_3(s)+2\text{Al}(s)⟶2\text{Fe}(l)+{\text{Al}}_2{\text{O}}_3(s)+\text{heat}$.