Q21.108 P - Chemistry: Molecular Nature Of Matter And Change

Question

Subterranean brines in parts of the United States are rich in iodides and bromides and serve as an industrial source of these elements. In one recovery method, the brines are evaporated to dryness and then melted and electrolyzed. Which halogen is more likely to form from this treatment? Why?

Step-by-Step Solution

Answer

Bromide oxidation is easier since it has a lower positive (negative) electrode potential. As a result, brine is a better source of bromine gas.

Step 1: Definition

It's an electrochemical process that involves passing a current between two electrodes through an ionized solution (the electrolyte) to deposit positive ions (anions) on the negative electrode (cathode) and negative ions (cations) on the positive electrode (cathode) (anode).

Step 2: Determining the halogen is more likely from this treatment

The reduction potentials of the relevant oxidation processes should be compared to determine which halogen is more likely to occur.

Because brines are high in iodides and bromides, ${\text{I}}^{\text{ - }}{\text{ and Br}}^{\text{ - }}$ gases, respectively, might potentially be oxidized by electrolysis to produce${\text{I}}_{\text{2}}{\text{ and Br}}_{\text{2}}$  gases.

- For iodide,

 $$\begin{gathered} {\text{2I}}^{\text{ - }}{\text{ + 2e}}^{\text{ - }}\to {\text{I}}_{\text{2}} \\ {\text{E}}^{\text{0}}\text{= - 0.53V} \end{gathered}$$

- For bromide,

 $$\begin{gathered} {\text{2Br}}^{\text{ - }}{\text{ + 2e}}^{\text{ - }}\to {\text{Br}}_{\text{2}} \\ {\text{E}}^{\text{0}}\text{ = - 1.07V} \end{gathered}$$

The oxidation happens more quickly when the electrode potential is less positive (more negative). 

Therefore, bromine gas is more likely to result from such a reaction.