Question

Can Fe³⁺ oxidises bromide to bromine under standard conditions?

Given: \[\ce{E^0_{{Fe^{3+}|Fe^{2+}}}}\] = 0.771 V

\[\ce{E^0_{{Br_{2}|Br^-}}}\] = −1.09 V

Answer 1

Required half cell reaction

\[\ce{2Br^- -> Br2 + 2e^-}\] `("E"_"ox"^0)` = −1.09 V

\[\ce{2Fe^{3+} + 2e^- -> 2Fe^{2+}}\] `("E"_"red"^0)` = +0.771 V

\[\ce{2Fe^{3+} + 2Br^- -> 2Fe^{2+} + Br2}\] `("E"_"cell"^0)` = ?

`"E"_("cell")^0 = ("E"_("ox")^0) + ("E"_("red")^0)`

= −1.09 V + 0.771

= −0.319 V

\[\ce{E^0_{cell}}\] is – ve; ΔG is +ve and the cell reaction is non spontaneous. Hence Fe³⁺ cannot oxidises Br⁻ to Br₂.