E-l Chromic Acid Baths
E‑2 Some Sensible Precautions:
First Aid Kits
Although the term "caustic" is often reserved for strong bases, the term is applicable to strong acids and oxidants as well. Concentrated acids (hydrofluoric, hydrochloric, sulfuric, fluorosulfuric, chlorosulfuric, nitric, chromic, phosphoric, trichloroacetic, glacial acetic, phenol) as well as concentrated bases (sodium, potassium, and ammonium hydroxides) are injurious to the human skin and especially to eyes, corrosive to laboratory apparatus and furniture, and destructive to clothing. If taken into the mouth or digestive tract caustic substances can produce widespread destruction of the mucous membranes and other tissues, which may be fatal. Fumes from some of them (particularly nitric acid and hydrochloric acid) are injurious to the respiratory tract and lung tissue if inhaled, and may result in fatal pulmonary edema. See Appendix 5: First Aid for Chemical Exposure, for details on dealing with chemical spills on skin and, in particular, for details on handling hydrofluoric acid and fluorosulfuric acid exposures.
Some of these substances have high heats of hydration; the thoughtless addition of water to concentrated sulfuric acid or to solid sodium hydroxide may result in violent heating with dangerous spatter. In reaction mixtures some caustic substances, particularly the oxidizing acids, may be involved in run‑away reactions which may result in eruption or explosion with considerable spatter and the possibility of harm to eyes and skin.
E‑1 CHROMIC ACID BATHS
Chromic acid cleaning solution ("Chromerge"), which is often used to remove residual hydrophobic films (oil, grease) from laboratory glassware, should be treated with respect. It is made up by adding sodium dichromate to concentrated sulfuric acid (carefully, with stirring, because considerable heat is evolved). Contact with the skin rapidly produces severe burns; contact with wood, paper, cloth, and other organic substances can produce a fire. Use only where necessary (e.g., with volumetric glassware); for other purposes use a phosphate‑based laboratory detergent instead. Chromic acid cleaning solution should not be used to remove more than very small amounts of intractable organic residues in flasks, as a violent reaction may take place. During use, the solution container and glassware should be standing in a tray large enough to contain the entire amount in case of spillage or breakage. Chromic acid cleaning baths should be placed in well ventilated areas since toxic, volatile chromium compounds may be formed.
E‑2 SOME SENSIBLE PRECAUTIONS FOR USING CAUSTIC LIQUIDS
Sensible precautions in handling caustic liquids include the following:
(1) Wear a face shield when there is a significant spatter hazard.
(2) Protect your clothes with a rubber apron or a laboratory coat.
(3) Wear rubber gloves when handling containers of caustic liquids.
(4) Work in a hood when any fumes (e.g., HCl, oxides of nitrogen) may be evolved
(5) Never pipette any substance by mouth.
(6) Use a funnel if pouring into a narrow‑mouth vessel.
(7) Never pour water or a reaction mixture into concentrated acid; pour the acid slowly,
or a small amount at a time, into the mixture.
(8) Wipe up small spills and bottle rings immediately, using rubber gloves and a wet cloth.
A large spill constitutes an emergency that requires notification of the laboratory
Spill Kits for mercury, caustic liquids, acids and flammable solvents are available in the instrument room ABB‑365. The mercury vacuum is located in ABB 107:. Strong acids spilled on the table top or the floor should be diluted with water. The diluted acid can then be neutralized cautiously with sodium bicarbonate (which is applied in solid form) and mopped up. Strong bases should be diluted and washed away or neutralized with solid sodium bisulfate or sodium dihydrogen phosphate. Beware of spatter in either case. Toxic acids such as chromic acid cleaning solution should not be neutralized in any significant quantity with bicarbonate as this may produce an airborne mist of chromic acid. A large spill of cleaning solution may be soaked up in a heavily applied layer of dry sand, which is then shovelled into a plastic bucket and carried immediately outside the building where it can be shovelled, a little at a time, into a pail of water. The site of the spillage should then be washed thoroughly; a neutralizer such as bicarbonate can be applied at this stage.
(9) In case of skin contact, wash the affected part immediately in cold running water.
A dilute (1%) acetic acid solution or vinegar may then be safely applied in the case of strong alkali. Sodium bicarbonate solutions or laboratory soap should be applied in the case of strong acid. In both cases this treatment should be followed by extensive washing with water. Obtain medical help if a chemical burn results. See Appendix 5 for more details.
Although hydrofluoric acid is a relatively weak acid, it is a very strong biological poison. Concentrated HF can be very insidious; since it produces no sensation of burning initially, it may stay trapped inside a leaky glove for hours in contact with the hand. Later, there may be extensive blistering and intense pain without the cause being immediately apparent. HF can penetrate very deeply in tissues resulting in very severe damage which may even require amputation. See Appendix 5-E for more details.
(10) In case of eye contact, immediately bathe the eyes in cool running water: subject the eyes to a copious (but not forceful) flow of water from the eyewash fountain located by the exit door; hold the eyelids thoroughly open to bathe the eyeballs and undersides of eyelids.
Summon medical help immediately (call 88). If alkali is involved, follow the washing with application of a 3% solution of boric acid. Time is of the essence; caustic alkali can destroy the cornea in as little as five minutes. CAUTION: Boric acid should be used externally for the eyes only. Boric acid is very toxic if taken internally, thus never take boric acid by mouth as an antidote for a base or for any other reason.
Eye wash fountains should be flushed for several minutes each week to minimize the build-up of microorganisms.
(11) In case of ingestion of caustics or inhalation of their fumes get medical aid immediately. Before aid arrives, a person who has ingested acid or alkali should be given a considerable amount of water to drink; sodium bicarbonate or magnesium oxide can then be safely administered in case of acid ingestion, or dilute (1%) acetic acid or vinegar or lemon juice in case of alkali. Never use BORIC ACID for internal use: it is highly toxic.
(12) A first aid kit is available in each lab. Supplies for it can be obtained from the undergrad technical staff in ABB‑412. Make sure the listed supplies are complete and that you know how to use them.
Acetic acid, 1% aqueous solution, 500 mL
Adhesive, 1/2", 1 roll
Antiseptic, 1 bottle
Boric acid, 3% aqueous solution
Gauze Pads, 6
Glycerol (for phenol burns)
Sodium thiosulfate (1% aqueous solution) for bromine burns
Ointment for fluorine burns (on request)
*Phenol, 1% in glycerol (for bromine burns)
*tetramethylammonium chloride, 10% aqueous solution (for fluorine and HF burns)
*Only present in labs where it is needed