explain indirect redox reaction with proper diagram and equation.
Answers
Explanation:
Considering the above diagram, the zinc rod/strip is oxidized to zinc (Zn2+) ions by direct electron transfer. Similarly, copper ions are reduced to the copper element by direct electron transfer. We know from above experiment, the connection of zinc and copper rods are external in order to complete the circuit and help in the transfer of electrons. The two half-reactions are as follows:
Oxidation Half-Reaction
Zn (s) → Zn2+ + 2e−
Reduction Half-Reaction
Cu2+ + 2e–→ Cu(s)
The element zinc loses electrons which the copper ions acquire to form metallic copper. Therefore, the overall redox reaction of zinc and copper is:
Cu2+ + Zn (s) → Cu (s) + Zn2+
Observation of the Redox Process in Zinc and Copper Cell
Zinc electrode release zinc atoms which get oxidized to its ionic form. This is because zinc is higher in the activity series in comparison to copper. Therefore, zinc is oxidized more easily than copper.
Zn (s) → Zn2+ + 2e−
The electrode where oxidation takes place is called anode. In this case, zinc anode slowly depreciates due to loss of zinc metal while the cell operates. Thus, the concentration of zinc ion will gradually increase because of electron generation at the anode. Therefore, it is the negative electrode.
The electron moves from zinc anode through the external wire and continues towards the copper electrode. As a result, voltmeter registers a reading. Finally, the electrons will enter the copper electron and combine with copper ions present in the solution to form the metallic copper.
Cu2+ (aq) + 2e– → Cu(s)
The reduction takes place in the copper electrode. It is also called a cathode. Gradually the mass of cathode will increase because of the formation of copper metal. However, the half-cell concentration of the copper (II) ions will decrease. Thus, cathode acts as a positive electrode.
The movement of the ions through the membrane helps in maintaining the neutrality in the cell. In the diagram of voltaic cell mentioned above, the sulfate ions will travel from the copper half-cell to the zinc half-cell to maintain the increase and decrease taking place in the copper and zinc ions, respectively.
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