Question

Sulfuric acid is a very strong acid that can act as an oxidizing agent at high concentrations (very low pH, or even negative pH values). Under standard conditions, sulfuric acid has a low reduction potential,

SO42−(aq)+4H+(aq)+2e−⇌SO2(g)+2H2O(l),   +0.20 V

which means it cannot oxidize any of the halides F2, Cl2, Br2, or I2. If the H+ ion concentration is increased, however, the driving force for the sulfuric acid reduction is also increased according to Le Châtlier's principle. Sulfuric acid cannot oxidize the fluoride or chloride anions, but it can oxidize bromide and iodide anions when there are enough H+ ions present. The standard reduction potentials of the halogens are as follows:

F2(g)+2e−Cl2(g)+2e−Br2(l)+2e−I2(s)+2e−→→→→2F−(aq),2Cl−(aq),2Br−(aq),2I−(aq),+2.87 V+1.36 V+1.07 V+0.54 V

The Nernst equation allows us to determine what nonstandard conditions allow the reaction to occur (have a positive  Ecell value).

The Nernst equation relates a nonstandard cell potential, Ecell, to the standard cell potential, E∘cell, and the reaction quotient, Q, by

Ecell=E∘cell−2.303RTnFlogQ

where R=8.314 J K−1 mol−1, T is the Kelvin temperature, n is the number of moles of electrons transferred in the reaction, and F=96485 C mol−1.

At 60.0 ∘C , what is the maximum value of the reaction quotient, Q, needed to produce a non-negative Ecell value for the reaction SO42−(aq)+4H+(aq)+2Br−(aq)⇌Br2(l)+SO2(g)+2H2O(l) In other words, what is Q when Ecell=0 at this temperature? Express your answer numerically to two significant figures.

Answer 1