Introduction Peroxo compounds play an important role in many areas including e.g. perborates or perc — Physical Chemistry — Kinetics Chemistry Question

Introduction
Peroxo compounds play an important role in many areas including e.g. perborates or percarbonates in the detergent industry or peroxo compounds for the whitening of a variety of products. Barium peroxide is one of the best-known peroxides. It can be prepared by the oxidation of barium oxide with oxygen in a reversible reaction. However, the peroxide content of BaO₂ is always lower than that calculated. Because of the reversibility of this reaction, barium peroxide provides a means of storage of elemental oxygen and several years ago, it was the only source of oxygen gas.

The peroxide content of such compounds can be determined by reaction with an excess of acid to give dihydrogen peroxide followed by a titration with a standard solution of potassium permanganate. This quantitative method is widely used in all areas where peroxides are of importance.

This practical exercise involves the preparation of strontium peroxide, determination of the strontium content by a complexometric titration and determination of the peroxide content by manganometric analysis.

List of chemicals
- Ammonia, aqueous solution, w(NH₃) = 0.25
- EDTA disodium salt, aqueous solution, c(Na₂EDTA) = 0.1 mol dm^-3
- Ethanol, w(C₂H₅OH) = 0.96
- Hydrogen peroxide, aqueous solution, w(H₂O₂) = 0.03
- Methyl red, solid
- Naphthol green B, solid
- Perchloric acid, aqueous solution, w(HClO₄) = 0.10
- Phthalein purple, solid
- Potassium permanganate, aqueous solution, c(KMnO₄) = 0.1 mol dm^-3
- Strontium chloride hexahydrate, solid

Procedure 1: Preparation of strontium peroxide
5.0 g of strontium chloride hexahydrate are dissolved in about 2.5 cm₃ of distilled water and 25 cm₃ of dihydrogen peroxide (w(H₂O₂) = 0.03) are added. A solution of 3.5 cm₃ of ammonia (w(NH₃) = 0.25) in 50 cm₃ of distilled water is added to the mixture to give strontium peroxide octahydrate on standing. The precipitate is filtered off, and dried at about 150 °C. In this procedure, the octahydrate transforms nearly completely into the anhydrous compound. An extremely small amount of water remains in the product and the peroxide content is slightly lower than calculated for SrO₂. At higher temperatures, strontium peroxide decomposes rapidly. Note: calcium peroxide can be prepared similarly.
Record the yield of the product in g.

Procedure 2: Manganometric determination of the peroxide content
About 100 mg of the product prepared in procedure 1 (record the exact weight) are transferred into a 300 cm₃ Erlenmeyer flask and the contents dissolved in 5 cm₃ of perchloric acid. The volume of the solution is increased to about 100 cm₃ by addition of water. The determination of the peroxide content is performed by titration with potassium permanganate solution (c(KMnO₄) = 0.02 mol dm^-3), until the solution is slightly pink in colour. At the beginning, the solution has to be titrated slowly because of the slow rate of reaction. The latter can be accelerated by the addition of a small amount of a manganese(II) compound.
Record the volume of the potassium permanganate solution used in the titration in cm₃.

Procedure 3: Complexometric determination of the strontium content
About 100 mg of the product prepared in procedure 1 (record the exact weight) are transformed into a 300 cm₃ Erlenmeyer flask and the contents dissolved in 5 cm₃ of perchloric acid. The solution is made up to a volume of 50 cm₃ and 15 cm₃ of ammonia solution, 60 cm₃ of ethanol and 2 cm₃ of phthalein purple indicator are added. The resulting deep purple solution is titrated with disodium EDTA solution (c(Na₂EDTA) = 0.1 mol dm^-3) until the solution is intense light-green in colour.
Record the volume of the Na₂EDTA solution in cm₃.

Preparation of the phthalein purple indicator
100 mg of phthalein purple, 5 mg of methyl red and 50 mg of naphthol green B are dissolved in 2 cm₃ of ammonia solution. The solution is filled up to a volume of 100 cm₃. The indicator is stable for up to a period of one week.