91Ó°ÊÓ

(a) Based on the table of standard reduction potentials, the substance with the largest standard reduction potential is the strongest oxidizing agent :${\text{Br}}_{\text{2}}$,${\text{Fe}}^{\text{3+}}$,${\text{Cu}}^{\text{2+}}$. The larger the standard reduction potential, the more likely the substance is to be reduced. The stronger the reduction of a substance, the stronger it is as an oxidizing agent. Given the following standard reduction potentials, the highest value is the strongest oxidizing agent, while the smallest/ most negative value is the weakest oxidizing agent. They have to be written in decreasing order, hence the order,${\text{Br}}_{\text{2}}{\text{,Fe}}^{\text{3}}{\text{,Cu}}^{\text{2}}$

$\begin{array}{ccc}\text{given}& {\text{E}}^{\text{°}}\text{(V)}& \text{rank}\\ {\text{Br}}_{\text{2}}& \text{1.07}& \text{1}\\ {\text{Fe}}^{\text{3+}}& \text{0.77}& \text{2}\\ {\text{Cu}}^{\text{2+}}& \text{0.34}& \text{3}\end{array}$

(b) Based on the table of standard reduction potentials, the substance with the largest standard reduction potential is the strongest oxidizing agent:${\text{Ca}}^{\text{2}}{\text{,Ag}}^{\text{†}}\text{,}$${\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}^{\text{2-}}$The larger the standard reduction potential, the more likely the substance is to be reduced. The stronger the reduction of a substance, the stronger it is as an oxidizing agent. Given the following standard reduction potentials, the highest value is the strongest oxidizing agent, while the smallest/ most negative value is the weakest oxidizing agent. They have to be written in increasing order, hence the order,${\text{Ca}}^{\text{2}}{\text{,Ag}}^{\text{†}}\text{,}$${\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}^{\text{2-}}$

$\begin{array}{ccc}\text{given}& {\text{E}}^{\text{°}}\text{(V)}& \text{rank}\\ {\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}^{\text{2-}}& \text{1.33}& \text{1}\\ {\text{Ag}}^{\text{+}}& \text{0.88}& \text{2}\\ {\text{Ca}}^{\text{2+}}& \text{-2.87}& \text{3}\end{array}$

Therefore, the work done is

${\text{(a)Br}}_{\text{2}}{\text{,Fe}}^{\text{3+}}{\text{,Cu}}^{\text{2+}}{\text{(b)Ca}}^{\text{2+}}{\text{,Ag}}^{\text{+}}{\text{,Cr}}_{\text{2}}{\text{O}}_{\text{7}}^{\text{2-}}\text{.}$