Question

A redox reaction involves oxidation and reduction. 

(a) What do you understand by electrode potential? 

(b) Define a redox couple. 

(c) Explain the set-up for Daniell cell with a diagram. 

(d) Write the electrode reactions and overall cell reaction which occur in the Daniel cell.

Answer 1

(a) The potential difference between metal and its own ion is called electrode potential. 

(b) A redox couple is defined as the combination of oxidised and reduced forms of a substance taking part in an oxidation or reduction half reaction. 

(c) Take copper sulphate solution in a beaker and put a copper strip. Take zinc sulphate solution in another beaker and put a zinc rod. The two redox couples are represented as Zn²⁺ /Zn and Cu²⁺/Cu. Put the beaker containing copper sulphate solution and beaker containing zinc sulphate side by side. Connect two solution by a salt bridge.

The Zn and Cu rods are connected by a metalic wire with a provision for ammeter and switch. Transfer of electrons now does not take place directly from Zn to Cu²⁺ , but through metallic wire. The electricity from solution in one beaker to solution in the other beaker flows by the migration of ions through the salt bridge.

(d) At Zn electrode (Anode):

Zn(s) ⟶ Zn²⁺(aq) + 2e^-

At cu electrode (Cathode):

Cu²⁺(aq) + 2e^- ⟶ cu(s)

Overall cell reaction:

Zn(s) + Cu²⁺(aq) ⟶ Zn²⁺(aq) + Cu(s)