Sulfuric acid is a very strong acid that can act as an oxidizing agent at high c

Question

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

SO42(aq)+4H+(aq)+2eSO2(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 Châtelier'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:

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

1 At 66.0 C , what is the maximum value of Q needed to produce a non-negative E value for the reaction

SO42(aq)+4H+(aq)+2Br(aq)Br2(aq)+SO2(g)+2H2O(l)

Explanation / Answer

E0SO42-,H+/SO2 = 0.20 V

E0Br2/Br- = + 1.07 V

E0cell = E0SO42-,H+/SO2 - E0Br2/Br- = 0.20 - 1.07 = - 0.87 V

Number of electrons transferred = 2 e

Applying Nernst equation for the cell reaction,

Ecell = E0cell - (0.0591/n)* LogQ

E0cell - (0.0591/n)* LogQ > 0

- 0.87 - (0.05916/2) LogQ > 0

- (0.0591/2)*LogQ > 0.87

LogQ > - 29.4

Q > 3.98*10-30

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