Question

A saturated aqueous copper (II) chloride is electrolysed using graphite anode and copper cathode as illustrated in diagram given below :

(i) Name the ions which will migrate to cathode.

(ii) Nametheions which will migrate to anode.

(iii) Which ion is likely to discharge at cathode and why?

(iv) Write ionic equation fòr reaction taking place atcathode.

(v) Which ion is likely to discharge at anode and why ?

(vi) Write ionic equation for reaction taking place at anode.

(vii) If electric current is passed for a very long time, state colour change taking place in electrolyte. State one reason for the change.

(viii) Give one reason for using graphite anode, rather than copper anode.

(ix) Name the gas liberated at cathode after the colour changes in electrolyte.

Answer 1

(i) Copper ions (Cu²⁺ ) and hydrogen ions H⁺ migrate to cathode.

(ii) Chloride ions (Cl^– ) and hydroxyl ions OH^– migrate to anode.

(iii) Copper ions (Cu²⁺ ) are likely to discharge at cathode, because their position is lower than hydrogen ions H+ in electrochemical series.

(iv) Cu²⁺ + 2e^– ⟶ Cu

(v) Hydroxyl ions (OH^– ) are likely to discharge at anode, because their position is lower than chloride ion (Cl^– ) in electrochemical series.

(vi) 4OH^– – 4e^– ⟶ 2H₂O + O₂ (g)

(vii) The electrolyte gets decolourised. It is because, the blue colour of electrolyte is due to the presence of Cu²⁺ ions. As Cu²⁺ ions discharge at cathode, therefore their concentration in electrolyte decreases. Thus, gradually blue colour fades away.

(viii) In such a situation the copper atoms on copper anode ionise and enter into electrolyte. Thus, size of copper anode gradually decreases. This is not possible in case of graphite anode.

(ix) Hydrogen gas is liberated at cathode.