Question

Fo

For redox titrations, the oxidation state of the analyte may need adjusting. The analyte can be preoxidized with an oxidizing agent to quantitatively oxidize the analyte, with the excess oxidizing agent eliminated to prevent interference with titration. Which of the oxidizing agents is paired with INCORRECT elimination chemistry?

Excess silver(I, III) oxide in mineral acid is eliminated by boiling, converting silver(III) cation to silver(I) cation.

Excess hydrogen peroxide in basic solution is eliminated by boiling, converting hydrogen peroxide to water and oxygen gas.

Excess solid sodium bismuthate is removed by filtration.

Excess stannous chloride in hot HCl is eliminated by boiling, converting stannous cation to stannic cation.

Excess peroxydisulfate is eliminated by boiling, converting the peroxydisulfate to sulfate.

Answer 1

(B)

In its pure form, Hydrogen Peroxide (H2O2) is a faintly bluish, syrupy liquid which boils at 150.2oC. It was first synthesized by the French chemist Louis Jaques Thenard in 1818 by acidification of Barium Peroxide (BaO2) with Nitric Acid (HNO3). This process was supplanted by an improved version in which the Barium Peroxide is initially treated with Hydrochloric Acid (HCl), followed by addition of Sulfuric Acid (H2SO4) to precipitate the Barium Ion (Ba2+) as Barium Sulfate (BaSO4). This leaves a relatively pure aqueous solution of Hydrogen Peroxide:

BaO2(s) + 2 HCl(aq) -----> H2O2(aq) + BaCl2(aq)

BaCl2(aq) + H2SO4(aq) -----> BaSO4(s) + 2 HCl(aq)

When exposed to sunlight or metallic impurities, Hydrogen Peroxide rapidly decomposes to Oxygen gas:

2 H2O2(aq) -----> 2 H2O(l) + O2(g)

This is a key reaction of Hydrogen Peroxide.