Question

Starting with a 30% (w/w) solution of hydrogen peroxide, how many mL would you need to dilute in order to end up with 25.00mL of a 3.6 M hydrogen peroxide solution? What are the hazards and safety precautions associated with 30% hydrogen peroxide. Assume a solution density of 1.11 g/mL.

Answer 1

Molarity of the 30% (w/w) H₂O₂ solution is calculated according to this formula

     mol/L = (%(w/w) * density * 10) / Molecular weight of H₂O₂

              = (30 * 1.11 * 10) / 34.01 = 9.79 mol/L

So, volume of required 30% (w/w) H₂O₂ solution is

   (25.00 * 3.6) / 9.79 mL = 9.19 mL

Delivery and Storage:

The methods available for delivery to bulk storage installations accommodate shipments of 70% hydrogen peroxide for dilution to the 35% or 50% storage concentrations. Solutions containing more than 8% hydrogen peroxide are classified by the U.S. Department of Transportation (DOT) as an oxidizer.

Under normal conditions hydrogen peroxide is extremely stable when properly stored. Rate loss in large containers such as tanks is less than 1% per year at normal ambient temperatures; in small containers, such as drums, rate loss is less than 2% per year. The larger the ratio of the storage container surface areas to the volume of hydrogen peroxide, the greater the rate loss.

Decomposition of hydrogen peroxide liberates oxygen and heat. In dilute solutions the heat evolved is readily absorbed by the water present. In more concentrated solutions, the heat raises the temperature of the solution and accelerates the decomposition rate. Special stabilizers are added during the manufacture of all grades of hydrogen peroxide to inhibit the catalytic decomposition effect of metals and other impurities that may accidentally contaminate the chemical during shipment, storage, and handling.

However, since no additive will prevent decomposition if excessive contamination occurs, the best practice is to prevent contamination through proper handling. All handling procedures must, therefore, be directed towards maintaining the same degree of purity and freedom from contamination as is maintained during the manufacturing process:

• Storage of hydrogen peroxide should be restricted to its original shipping container or to properly designed containers made of compatible materials which have been thoroughly passivated.
• Hydrogen peroxide that has been removed from the original shipping container should not be returned to it.
• All containers must be properly vented, and preferably stored away from sources of direct heat and combustible materials.
• Adequate ventilation and ample water supply for thorough flushing of accidental spillage on personnel and property should be provided.
• Hydrogen peroxide itself will not burn, but its decomposition liberates oxygen which supports combustion. Fires involving hydrogen peroxide are best controlled by using large quantities of water.

Hydrogen peroxide is not considered an explosive. However, when it is mixed with organic substances at significant concentrations, hazardous impact-sensitive compounds may result. Small amounts of other materials that contain catalysts (silver, lead, copper, chromium, mercury, and iron oxide rust) can cause rapid decomposition and an explosive pressure rupture of the containing vessel if it is not properly vented.

In addition to accelerated decomposition through contamination, the decomposition rate of hydrogen peroxide is increased with alkalinity, contact with certain materials of construction, and increasing temperatures. The rate of decomposition increases approximately 2.2 times for each 10 degrees C rise in temperature in the range from 20 degrees C to 100 degrees C, or 1.5 times for each 10 degrees F rise from 68 degrees F to 212 degrees F.

Decreasing temperatures have little effect on hydrogen peroxide until they drop substantially below 0 degrees C. Crystals do not begin to appear in 35% and 50% solutions until -33C (-27.4F) and -52.2C (-62F), respectively.

Eye Protection:

Hydrogen peroxide and its decomposition products are not systematic poisons but contact with hydrogen peroxide can be irritating. Concentrated vapors cause discomfort in the mucous membranes and the eyes. Contact of the eyes with hydrogen peroxide is particularly dangerous because corneal burns can occur very rapidly. Therefore, safety glasses or, preferably, goggles should always be worn when handling concentrated hydrogen peroxide. If, however, any hydrogen peroxide does get in the eyes, flush eyes thoroughly with water and consult a physician promptly.

Protective Clothing:

In addition to eye protection, rubber gloves and suitable protective clothing such as aprons or coveralls made of polyester acrylic fiber, polyvinyl chloride, polyethylene, or neoprene should be worn when handling concentrated hydrogen peroxide. Protective clothing, which lacks fire resistance, must be washed thoroughly with water should it come in contact with hydrogen peroxide. If allowed to dry in the fabric, the chemical may cause fire, particularly if the clothing is soiled.

Contact with moderate concentrations of hydrogen peroxide will cause whitening of the skin and stinging sensations. The whitening is due to the formation of gas bubbles in the epidermal layer of the skin. The stinging, in most cases, subsides quickly after thorough washing, and the skin gradually returns to normal without any damage. Highly concentrated hydrogen peroxide can cause blistering if left on skin surfaces for any length of time.

Inhalation of hydrogen peroxide vapors can cause irritation and inflammation of the respiratory tract. For this reason, the American Conference of Government Industrial Hygienists has determined a Threshold Limit Value (LTV) or 1 ppm (1.4mg/m3) of hydrogen peroxide vapor in air as a maximum exposure limit for any eight-hour workday of a normal 40-hour work week. If hydrogen peroxide vapor is inhaled, fresh air should be sought at once; if the inhalation has been prolonged, a physician should be consulted immediately.

Accidental Swallowing:

Hydrogen peroxide, a mild disinfectant, is useful in counteracting various microorganisms. Because of their antiseptic action, dilute hydrogen peroxide solutions (3% or less) are frequently used to treat open wounds and can be used as a gargle or mouthwash. However, contact or concentrated solutions (over 3%) with the members of the mouth is to be avoided. Under no circumstances should hydrogen peroxide be taken internally. If hydrogen peroxide is swallowed, drink water immediately to dilute, and contact a physician but do not attempt to cause vomiting.

In using hydrogen peroxide, safety should be first in the minds of everyone, and as with any other chemical, initial steps should be taken to familiarize all personnel with its safe and proper handling. Acceptance of hydrogen peroxide in a wide variety of industrial applications is a reflection of its simplicity in use.

Maximum safety in handling hydrogen peroxide is assured through the use of proper materials of construction, recognition of the need for venting in storage, and overall avoidance of contamination. The oxygen and water by-products of decomposition are innocuous, but splashing, inhaling vapor, and ingesting hydrogen peroxide must be avoided. If by unusual circumstances an accident should take place, flushing with large quantities of plain water is the simple corrective action needed. By adhering to straight-forward common sense procedures, every aspect of your operation will be aimed toward safety and a clean environment.