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Activity Series (OR) Electro chemicals series

Question

Four colourless salt solutions are placed in separate test tubes and a strip of copper is placed in each. Which solution finally turns blue?

Moderate

A

Pb(NO₃)₂
B

Zn(NO₃)₂
C

AgNO₃
D

Cd(NO₃)₂

Solution

$E_{{Zn}^{+ 2} / Zn}^{o} < E_{{Cd}^{+ 2} / Cd}^{o} < E_{{Pb}^{+ 2} / Pb}^{o} < E_{H^{+} / H_{2}; Pt}^{o} < E_{{Cu}^{+ 2} / Cu}^{o} < E_{{Ag}^{+} / Ag}^{o}$
Order of Oxidising power ${Zn}^{+ 2} < {Cd}^{+ 2} < {Pb}^{+ 2} < H^{+} < {Cu}^{+ 2} < {Ag}^{+}$
Order of Reducing power $Zn > Cd > Pb > H_{2} > Cu > Ag$
Blue colour is due to formation of Cu⁺² which is possible when Cu looses 2 electrons. All electrodes having SRP values lesser than SRP of Cu reduces Cu⁺² and that electrode having SRP greater than SRP of Cu oxidises Cu metal to Cu⁺².SRP of Ag electrode is more than SRP of Cu electrode hence AgNO₃solution turns to blue.

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