Question

During the electrolysis of copper (II) sulphate solution using platinum as cathode and carbon as anode :
(i) What do you observe at the cathode and at the anode?
(ii) What change is noticed in the electrolyte?
(iii) Write the reactions at the cathode and at the anode.

Answer 1

• Step 1 : Definition
  Cathode: A cathode is an negatively charged electrode.
  Anode: An anode is a positively charged electrode.
• Step 2 : Observation at the cathode and at the anode
  At cathode : Reddish-brown deposition of copper occurs at the cathode.
  At anode : Colourless gas is evolved at the anode.
• Step 3 : Change is noticed in the electrolyte
  ${\mathrm{Cu}}^{2+}$ discharge in preference to ${\mathrm{H}}^{+}$due to low discharge potential. Due to this the blue colour of the electrolyte fades as ${\mathrm{Cu}}^{2+}$ ions gradually migrate at cathode.
  Therefore, the blue electrolyte turns colourless.
• Step 4 : Reactions at the cathode and at the anode :

(iii) The reactions at the cathode and at the anode,

• At cathode :
  ${\mathrm{Cu}}^{2+}(\mathrm{aq}.)+2{\mathrm{e}}^{-}⟶\mathrm{Cu}\left(\mathrm{s}\right)$
• At anode :
  ${\mathrm{OH}}^{-}(\mathrm{aq}.)-1{\mathrm{e}}^{-}⟶\mathrm{OH}(\mathrm{aq}.)$
  $4\mathrm{OH}(\mathrm{aq}.)⟶2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\uparrow$