safety-in-academic-chemistry-laboratories-students

Keep perchloric acid bottles on glass or ceramic

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Unformatted text preview: id on laboratory benches made of wood or other combustible material. Keep perchloric acid bottles on glass or ceramic secondary containment trays with edges that are high enough to hold all the acid if the bottle breaks. Always digest organic matter with nitric acid before adding perchloric acid. Note that if sulfuric acid is added to dehydrate perchloric acid, an excessive dehydration may produce anhydrous perchloric acid, which is explosive at ordinary temperatures. Do not mix sulfuric or phosphoric acid with perchloric acid. Perchlorate esters have the same shattering explosive effect as nitroglycerine. Transition-metal perchlorates also can explode. 22 students short index 1/15/03 12:45 PM Page 23 Dry picric acid is highly explosive; you should only use it when necessary and if you thoroughly understand its hazards. Although picric acid is not explosive when wet, water may evaporate and leave it a dry, hazardous solid. Be certain that the picric acid contents are moist before opening a bottle of picric acid; of particular concern is the possibility that explosive peroxides may have formed in the cap threads. If there is any question about the safety of opening a bottle of old picric acid, immerse the bottle in water and slowly twist the cap to allow water to dissolve any crystals. Water can then be safely added to moisturize the picric acid. The most common bases used in academic laboratories are the alkali metal hydroxides and aqueous solutions of ammonia. Sodium and potassium hydroxides are strong bases and are extremely destructive to the skin and the eyes. Be cautious when you prepare concentrated solutions of these bases. The high heat of the solution can raise the temperature to dangerous levels—high enough to cause boiling and splattering. Ammonia in aqueous solution is a weak base, sometimes erroneously called “ammonium hydroxide.” The vapors of aqueous ammonia solutions are irritating and toxic. A Few Examples of Toxic Materials Halogens. All halogens are toxic oxidizing agents—especially...
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