Key Properties of Hydrogen Peroxide
Hydrogen peroxide with the formula H2O2 is a colorless water soluble liquid. The molecule of hydrogen peroxide is asymmetrical and strongly polarized. A high tendency to form hydrogen-bond networks causes higher viscosity than water.
Typical Properties of Hydrogen Peroxide
Because of free electron pairs on both oxygen atoms, the H2O2-molecule tends to form donor-acceptor compounds. Pure hydrogen peroxide is primarily of scientific interest only. However, its aqueous solutions are widely used in cleaning and sanitization, electronics, mining, chemical synthesis, the bleaching of textiles, laundry and hair care, in the pulp and paper industry, as a sustainable rocket fuel, antiseptic, antichlor, seed disinfectant, as a bleach and oxidizing agent in food and fish farming or as a substitute for chlorine in water and wastewater treatment.
The molecular structure as well as oxygen's oxidation state define the chemical properties of hydrogen peroxide. The oxygen atom, being in the oxidation state I, allows hydrogen peroxide to participate in both oxidation as well as reduction reactions.
Although hydrogen peroxide is well known as a peroxide and powerful oxidizing agent with disinfectant, antiviral and antibacterial activities; its reduction properties play an important role in some applications. Typical chemical reactions, in which hydrogen peroxide is involved, are oxidation and reduction reactions, formations of other peroxygen or adduct compounds. In contrast to many other redox agents, hydrogen peroxide introduces no additional substances other than water into the reaction system and an excess can be easily decomposed into water and oxygen, not interfering thereby with subsequent reaction steps. Hydrogen peroxide solutions are often considered true "green chemistry."
Despite its high reactivity, pure hydrogen peroxide is a stable substance and, if kept under optimal conditions, can be stored for years. The most important factors increasing the rate of decomposition are high pH value, high temperatures, UV irradiation, presence of transition metal salts and all kinds of impurities.
The decomposition of peroxide hydrogen into oxygen and water is a quite complex process, which involves formation of various free radicals that destroy pathogens and prevent spreading of infection. In some applications such as soil remediation the induced instability is intentionally caused and used.
Important physical properties of hydrogen peroxide and its aqueous solutions are summarized in the table below.
Properties of Aqueous Hydrogen Peroxide Solutions
| H2O2 Concentration* | % (wt.) | 0 | 30 | 35 | 50 | 60 | 70 | 100 |
|---|---|---|---|---|---|---|---|---|
| g(H2O2)/kg | 300 | 350 | 500 | 600 | 700 | |||
| g(H2O2)/l | 332 | 395 | 596 | 742 | 899 | |||
| mol/l | 9.8 | 11.6 | 17.5 | 21.8 | 26.4 | |||
| mol/% | 18.5 | 22.2 | 34.6 | 44.3 | 55.3 | |||
| Hydrogen peroxide content | % (wt.) | 0 | 14.1 | 16.5 | 23.5 | 28.2 | 32.9 | 47.1 |
| Molecular weight | g/mol | 18.015 | 34.015 | |||||
| Density at 20 °C | g/ml | 0.998 | 1.111 | 1.131 | 1.195 | 1.241 | 1.289 | 1.450 |
| Freezing point | °C | 0 | -26 | -33 | -52 | -56 | -40 | -0.4 |
| Boiling point at 1013 mbar | °C | 100 | 106 | 108 | 114 | 119 | 125 | 150 |
| Boiling point at 2026 mbar | °C | 132 | 135 | 145 | 152 | 158 | ||
| Boiling point at 3039 mbar | °C | 147 | 150 | 161 | 168 | 176 | ||
| Total vapor pressure (30 °C) | mbar | 42 | 33 | 32 | 14 | 19 | 15 | 8 |
| mm. Hg. | 31.6 | 25 | 24 | 18 | 14 | 11 | 6 | |
| H₂O₂ partial vapor | mbar | 0.3 | 0.4 | 0.8 | 1.2 | 1.7 | ||
| Pressure at 30 °C | mm. Hg. | 0.25 | 0.3 | 0.6 | 0.9 | 1.3 | ||
| Specific heat at 25 °C | J*g/K | 4.2 | 3.6 | 3.5 | 3.3 | 3.2 | 3.1 | 2.6 |
| Refractive index, n25D at 25 °C | 1.3325 | 1.3519 | 1.3554 | 1.3661 | 1.3734 | 1.3814 | 1.4067 | |
| Viscosity at 20 °C | mPa*s | 1.00 | 1.11 | 1.12 | 1.18 | 1.21 | 1.23 | 1.25 |
| Surface tension at 20 °C | mN/m | 72.8 | 74.2 | 74.5 | 75.7 | 76.4 | 77.3 | 80.4 |
The tabulated values, which are given above, describe the physico-chemical properties of salt free pure aqueous solutions of peroxide hydrogen in water.
*Hydrogen peroxide concentration can be expressed in weight percent, gram of 100%-age hydrogen peroxide in 1 kg solution, gram of 100%-age hydrogen peroxide in 1L solution and as molar concentration or molar fraction of hydrogen peroxide in solution. The tabulated values for g(H2O2)/l and mol/l are given for the temperature of 25 °C.