Question

Use the emf series (Appendix D) to arrange the species.

(a) In order of decreasing strength as oxidizing agents:${\mathbf{\text{Fe}}}^{\mathbf{\text{3+}}}{\mathbf{\text{,Br}}}_{\mathbf{\text{2}}}{\mathbf{\text{,Cu}}}^{\mathbf{\text{2+}}}$

(b) In order of increasing strength as oxidizingagents :${\mathbf{\text{Ca}}}^{\mathbf{\text{2+}}}\mathbf{\text{,}}$${\mathbf{\text{Cr}}}_{\mathbf{\text{2}}}{\mathbf{\text{O}}}_{\mathbf{\text{7}}}^{\mathbf{\text{2-}}}$,${\mathbf{\text{Ag}}}^{\mathbf{\text{+}}}$

Short answer

The required work use the emf series increasing and decreasing order strength as oxidizing agents given the highest and smallest value.

Step-by-step solution

Find largest and smallest reduction in decreasing order

(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,${\text{Br}}_{\text{2}}{\text{,Fe}}^{\text{3}}{\text{,Cu}}^{\text{2}}$

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

Find largest and smallest reduction in increasing order

(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

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