Electrochemical Series - Practice Questions & MCQ

Characteristics of Electrochemical Series
Metals with greater negative E^o (reduction) are strongly electropositive and have more reactivity. It means a lower placed element or metal is in the given series is less reactive is replaced by upper placed or higher element while higher element can be coated by lower metal.
Example, (i) $\mathrm{Zn}+\mathrm{CuSO}_4 \rightarrow \mathrm{ZnSO}_4+\mathrm{Cu}$
Here Cu is replaced by Zn due to more oxidation potential or reactivity of Zn, while Zn is coated by Cu. Zn- Cu couple is also coated by Cu. Here, the solution turns from blue to colorless and the rod becomes Reddish-brown from Gray white.
(ii) $\mathrm{Cu}+2 \mathrm{AgNO}_3 \rightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2+2 \mathrm{Ag}$
Here solution becomes colorless to blue and the rod becomes reddish-brown to white.

• Metals above H₂ can easily replace H₂, from acid, bases, etc. due to their more positive E^o_op or reactivity.
  For example,
  $\begin{aligned} & \mathrm{Mg}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{MgSO}_4+\mathrm{H}_2 \\ & \mathrm{E}_{\mathrm{op}}^{\circ} \text { of } \mathrm{Mg}>\mathrm{E}_{\mathrm{OP}}^{\circ} \text { of } \mathrm{H}_2 \\ & \mathrm{R}-\mathrm{OH}+\mathrm{Na} \rightarrow \mathrm{R}-\mathrm{ONa}+\mathrm{H}^{+}\end{aligned}$
• Lower placed metals (Cu Hg Ag Pt Au) to H₂ can not do that as E^o_op of H₂ is more than their E^o_op.$\mathrm{Cu}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow$ no reaction
• Oxides of lower metals (Cu, Hg, Ag, Pt, Au) are easily reduced by H₂ or carbon. As they are thermally more unstable due to positive E_rp, they also decomposed on heating.
• More E^o_OP means more ease or tendency to get oxidize that is, the act as better reducing agents while more E^o_RP means more ease to reduced that is, they act as better oxidizing agents. It means metal above hydrogen having positive E_op are reducing agents.
  Reducing property $\propto \mathrm{E}_{0 \mathrm{O}}^{\circ}$
  For example, Li is the strongest reducing agent due to maximum E^o_OP
• Metals placed lower in reactivity series (Cu Hg Ag Pt Au) having high E^o_RP are oxidizing agents and they have tendency to be reduced.
  
  For example, Oxidizing power $\propto \mathrm{E}_{\mathrm{RP}}$ $\mathrm{F}_2>\mathrm{Cl}_2>\mathrm{Br}_2>\mathrm{I}_2$
  
  Reducing power decreases As
• $\mathrm{E}_{\mathrm{op}}^{\circ}$ of $\mathrm{I}^{-}>\mathrm{Br}^{-}>\mathrm{Cl}^{-}>\mathrm{F}^{-}$
• Elements with more positive E^o_RP will be discharged first at cathode i.e., discharging order increases as reduction potential increases.

            Increasing ease of deposition of some cations

            $\mathrm{Li}^{+}, \mathrm{K}^{+}, \mathrm{Ca}^{+2}, \mathrm{Na}^{+}, \mathrm{Mg}^{+2}, \mathrm{Al}^{+3}, \mathrm{Zn}^{+2}, \mathrm{Fe}^{+2}, \mathrm{H}^{+}, \mathrm{Cu}^{+2}, \mathrm{Ag}^{+}, \mathrm{Au}^{+3}$

• In case of negative ions, anion with stronger reducing nature is discharged first at anode.

Increasing ease of discharge of some anion

$
\mathrm{SO}_4^{-2}<\mathrm{NO}_3^{-}<\mathrm{OH}^{-}<\mathrm{Cl}^{-}<\mathrm{Br}^{-}
$

• Hydroxides of upper metals are strongly basic and their salts do not undergo hydrolysis while hydroxides of lower metals are weakly acidic and their salts undergo hydrolysis.