Why does the voltage increase when ammonia is added to a Cu2+ cell??
The voltage of a Cu2+ cell increases when ammonia is added due to the formation of a complex ion between Cu2+ and ammonia. Here are the step-by-step explanations:
1. In the Cu2+ cell, Cu2+ ions are reduced at the cathode, gaining two electrons to form Cu atoms: Cu2+ + 2e- -> Cu.
2. At the anode, copper atoms are oxidized, losing electrons to form Cu2+ ions: Cu -> Cu2+ + 2e-.
3. When ammonia (NH3) is added to the solution, it reacts with the Cu2+ ions to form a complex ion known as tetraamminecopper(II) complex, [Cu(NH3)4]2+.
4. The formation of this complex ion lowers the concentration of Cu2+ ions in the solution, leading to a decrease in Cu2+ concentration at the anode.
5. According to Le Chatelier's principle, when the concentration of Cu2+ ions decreases at the anode, the equilibrium will shift to the right to counteract this change. This means more Cu atoms will be oxidized to form Cu2+ ions, resulting in an increased rate of the oxidation reaction.
6. The increased rate of oxidation at the anode leads to a higher potential difference (voltage) across the cell.
In summary, the addition of ammonia to a Cu2+ cell forms a complex ion that decreases the concentration of Cu2+ ions, causing the cell's equilibrium to shift and increase the rate of oxidation, resulting in a higher voltage.
When ammonia is added to a Cu2+ cell, the voltage increases due to a phenomenon called complexation. In this case, ammonia acts as a ligand and forms a complex with the Cu2+ ions present in the cell.
To understand why the voltage increases, we need to consider the electrochemical cell and its components. In a typical Cu2+ cell, there are two half-cells:
1. Anode: Consists of a strip of copper (Cu) that oxidizes, losing electrons and forming Cu2+ ions according to the reaction: Cu → Cu2+ + 2e−
2. Cathode: Consists of another metal or substance capable of accepting electrons. In this case, Cu2+ ions are reduced to copper metal (Cu) by gaining electrons according to the reaction: Cu2+ + 2e− → Cu
The voltage of the cell is determined by the difference in reduction potentials between the two half-cells. Reduction potential is a measure of the tendency of a half-reaction to occur as a reduction process.
When ammonia (NH3) is added to the Cu2+ cell, it forms a complex with the Cu2+ ions. This complex, known as tetraamminecopper(II) complex, is represented as [Cu(NH3)4]2+.
The addition of ammonia to the Cu2+ cell increases the concentration of the [Cu(NH3)4]2+ complex, while decreasing the concentration of free Cu2+ ions. The reason behind the increase in voltage is that the reduction potential of the Cu2+ to Cu reaction decreases in the presence of the complex.
The reduction potential of a half-reaction depends on various factors including concentration and complex formation. In this case, the formation of the [Cu(NH3)4]2+ complex shifts the equilibria between Cu2+ and Cu, leading to a decrease in the reduction potential of the Cu2+ to Cu half-reaction.
This decrease in reduction potential means that the Cu2+ ions are more easily reduced to copper at the cathode, resulting in an increase in the voltage of the cell.
Therefore, the addition of ammonia to a Cu2+ cell increases the voltage due to the formation of a complex that alters the reduction potential of the Cu2+/Cu half-reaction.