Question

Given, Fe3+ (aq) + e- $\to $Fe2+ (aq);${{E}_{o}}=+0.77V$
Al3+ (aq) + 3e- $\to $ Al;${{E}_{o}}=-1.66V$
Br2 (aq) + 2e- $\to $2Br-;${{E}_{o}}=+1.09V$
Considering the electrode potentials, which of the following represents the correct of reducing power?
A. Al$<$Fe2+$<$Br-
B. Fe2+$<$Al$<$Br-
C. Br- $<$Fe2+ $<$Al
D. Al $<$Br- $<$Fe2+

Answer 1

Hint In electrochemistry electrode potential is defined as the electromotive force of a galvanic cell produced from a standard reference electrode and another electrode. The reference electrode is the standard hydrogen electrode and defined to have zero volts potential.

Complete Step by step solution:
Due to the transfer of charged species across the interface electrode potential occurs between an electrode and electrolyte. In an electrochemical cell two types of electrode are present which are named as cathode which attracts positively charged electrons and the anode which attracts negatively charged electrons and both have a certain electrode potential and difference between cathode and anode is known by the cell potential.
Reducing power of electrodes calculates the tendency of a chemical species to acquire electrons from an electrode or to lose an electron to an electrode therefore it is considered to be reduced or oxidized respectively. Redox potential can be measured in volts or millivolts. Each species has its own intrinsic redox potential which can be defined as the more positive the value of reduction potential, greater is the affinity for electrons and has a greater tendency to be reduced. In aqueous solutions redox potential finds the tendency of the solution to either gain or lose electrons when it is subjected to change by introduction of a new species. A solution with a higher reduction potential than the new species will have a tendency to gain electrons from the new species and a solution with a lower reduction potential will have a tendency to lose electrons to the new species.
Hence we can say that, negative ${{E}_{o}}$ means that the redox couple is a stronger reducing agent. So we can say that aluminum is the strongest reducing agent out of three as it has a negative ${{E}_{o}}$ value.

So the order of option C is correct.

Note: Reducing agent is an element or compound that loses or donates an electron to an electron oxidizing agent in a redox chemical reaction. A reducing agent is said to be oxidized when it loses electrons in the redox reaction. A reducing agent typically is in one of its lower possible oxidation states which is known as the electron donor. Examples of reducing agents include the earth metals are formic acid, oxalic acid, and sulfite compounds.