Question

Consider the following standard oxidation potentials $\left(\text{at}{25}^{\circ }\text{C}\right)$
$E_{Ag|A{g}^{+}}^{\circ }:-0.799\text{V};E_{Hg|H{g}^{2+}}^{\circ }:-0.789\text{V};E_{Mg|M{g}^{2+}}^{\circ }:+2.37\text{V};$
$E_{Mn|M{n}^{2+}}^{\circ }:+1.18\text{V};E_{Sn|S{n}^{2+}}^{\circ }:0.136\text{V}$.
Which of the following statement(s) is/are incorrect under standard conditions?

• A. $Sn$ can displace $Mg$ and $Ag$ from their solutions
• B. $Ag$ can displace $Hg$ and $Mg$ from their solutions
• C. $Mn$ can displace $Sn,Hg$ and $Ag$ from their solutions
• D. $Mn$ can displace $Sn,Mg$ and $Hg$ from their solutions

Answer 1

Answer: (A), (B), (D)

$Mn$ can displace $Sn,Mg$ and $Hg$ from their solutions

Displacement reaction takes place only when the metal displacing has higher $E^o$ value

1. Since $Sn$ has lower $E^o$ than $Mg$ therefore it can’t displace $Mg$ however it has higher $E^o$ than $Ag$ therefore it can displace $Ag$ from its solution.
2. Since $Ag$ has lower $E^o$ than $Hg$ and $Mg$ therefore it can’t displace both $Hg$ and $Mg$ from their solutions.
3. Since $Mn$ has higher $E^o$ than $Sn$, $Hg$ and $Ag$ therefore it can displace $Sn$, $Hg$ and $Mg$ from their solutions.
4. Since $Mn$ has lower $E^o$ than $Mg$ therefore it can’t displace $Mg$ however it has higher $E^o$ than $Sn$ and $Hg$ therefore it can displace $Sn$ and $Hg$ from its solutions.