Hydrogen peroxide

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Hydrogen peroxide
Names
IUPAC name
Hydrogen peroxide
Other names
Dioxidane
Oxidanyl
Perhydroxic acid
Properties
H2O2
Molar mass 34.0147 g/mol
Appearance Very light blue liquid (conc.)
Colorless liquid (dil.)
Odor Slightly sharp
Density 1.450 g/cm3 (20 °C, pure)
1.11 g/cm3 (20 °C, 30% aq. solution)
Melting point −0.43 °C (31.23 °F; 272.72 K)
Boiling point 150.2 °C (302.4 °F; 423.3 K)
Miscibility
Solubility Reacts with ketones
Soluble in alcohol, ether
Insoluble in benzene, chloroform, petroleum ether, toluene
Vapor pressure 5 mmHg (30 °C)
Acidity (pKa) 11.75
Thermochemistry
−187.80 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (30%)
Flash point Non-flammable
Related compounds
Related compounds
Water
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Hydrogen peroxide is a mostly clear, blue-ish liquid with similar melting and boiling points to water. It is a powerful and versatile oxidizer, but can act as a reducing agent in some circumstances. It also acts as a very weak acid (pKa 11.6), forming hydrated peroxide salts (such as sodium peroxide octahydrate) with alkalis in aqueous solution.

Properties

Chemical

Hydrogen peroxide can be used as an oxidizer, and may enhance the oxidizing capabilities on mixing. For example, a mixture of sulfuric acid and hydrogen peroxide will react faster than the acid alone. Hydrogen peroxide is dangerous as it can cause explosions when in contact with combustible materials in high concentration. An acid mixture of hydrogen peroxide and hydrochloric acid behaves like an oxidizing acid, similarly to nitric acid, and reacts with non-reactive metals such as copper.

Hydrogen peroxide disproportionates into water and oxygen gas. This happens rapidly at high temperatures or when a catalyst, such as Manganese dioxide or Potassium iodide, is added and this is often used to produce oxygen gas in a home chemistry setting.

Physical

Hydrogen peroxide is tinted slightly blue in high concentrations. It has boiling and melting points similar to water, but can be concentrated by fractional crystallization. Concentrations of peroxide 30% and above are considered concentrated.

Availability

Hydrogen peroxide is available readily as a disinfectant in pharmacies and grocery stores, but may only be obtained easily in low concentrations often as 3% or 6% solutions.

Higher concentration peroxide is sold for animal disinfectants, pool/spa treatments, hair bleaching. Some may contain other chemicals, including stabilizers, so read the label first.

Preparation

Hydrogen peroxide can be prepared by reacting concentrated sulfuric acid and barium peroxide.

BaO2 + H2SO4 → H2O2 + BaSO4

The insoluble barium sulfate is filtered from the mixture.

Due to the availability of low concentrations of peroxide worldwide, concentrated hydrogen peroxide solutions are often prepared by evaporating the water from the peroxide, making sure not to boil the solution (as this will break down the peroxide).

One of the earliest large scale production of hydrogen peroxide involves the electrolysis of a solution of sulfuric acid of 50% concentration, or ammonium bisulfate solution. The resulting hydrogen peroxide solution has a concentration of 30%.

While sulfuric acid is more readily available, the ammonium bisulfate process is cheaper and has a higher cell efficiency. The electrolysis is carried out in stoneware tanks with platinum electrodes; conversion of bisulfate to the persulfate takes place at the anode. After hydrolysis of the persulfate (with steam) in an evaporator, the resulting dilute aqueous solution of H2O2 is separated from the bisulfate and further distilled in a stoneware distillation column. The resulting solution is approximately 30 w/o H2O2. Both the cathode liquor (after purification) and the bisulfate from the evaporator (and separator) are recycled back to the cells.

Projects

Handling

Safety

As it is an oxidizer, high concentrations of hydrogen peroxide can ignite or detonate combustible or explosive materials. Lower concentrations are much safer, but regardless of concentration, poisonous. Concentrated hydrogen peroxide leaves weak itching or stinging burns and a white discoloration on skin.

Storage

Hydrogen peroxide solutions are best stored in cold dark places, such as a fridge. High concentration peroxides are metastable and will slowly build-up pressure, so it's recommended to open the bottles from time to time, to release the pressure, and store the solutions with ample headroom in the bottles. Phosphoric acid and EDTA are added as stabilizers.

NEVER store hydrogen peroxide near volatile organic compounds, such as acetone, as there is a risk of forming acetone peroxide.

Concentrated solutions of hydrogen peroxide are known to slowly react with glass. This does not harm the glass significantly, but it does harm the peroxide: the reaction yields sodium hydroxide, which can provoke its decomposition. It is preferable to use polyethylene to store such solutions.

Disposal

Hydrogen peroxide can be decomposed by adding a catalyst, such as manganese dioxide or iron oxides (ordinary rust will do). This method however should not be used to neutralize concentrated peroxide as the decomposition will generate lots of heat and can lead to explosion. The explosion that crippled the Kursk submarine for example, occured when the peroxide that leaked from a torpedo entered in contact with some rust. It's recommended to not be poured down the drain, as it will quickly decompose in the sewage and may pose an explosion hazard. Adding a sulfide, such as lead(II) sulfide, will result in lead(II) sulfate and water.

References

Relevant Sciencemadness threads