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fumes will quickly corrode metal cabinets.
• Nitric acid is a strong oxidizing agent. Concentrated nitric acid must be stored in a separate liquid-tight compartment within an acid cabinet. If nitric acid is mixed with a flammable organic compound, such as acetic acid, the heat from the oxidation and neutralization reactions is enough to ignite the flammable material. Nitric acid also slowly destroys its red plastic bottle cap. Always replace with a new red cap. Nitric acid may turn yellow over time because of the release of nitrogen dioxide on exposure to light. The yellow color does not affect the product’s usefulness in the teaching laboratory.
• Glacial acetic acid is a flammable liquid. It should be stored in an acid cabinet, but in a location isolated from possible contact with nitric acid. Glacial acetic acid freezes at 16.6 °C; the material may crystallize in a cool storeroom. If this occurs, allow the bottle to warm up to ambient (25 °C) temperature.
• Concentrated sulfuric acid is a strong dehydrating agent. Because of its strong ability to remove water, it reacts violently with many organic materials such as sugar, wood, and paper. If sulfuric acid has turned brown, it has probably been contaminated with an organic material and its purity should be in question.
ACID SAFETY continued on next page.
202
Acid Safety
Safety Tips for Using Acids in School Labs
Introduction
The use of acids is an important compo- nent of most chemical laboratories. Understanding the properties and hazards of acids is an important first steps for the safe purchase, storage, use, and disposal of acids.
Safety Precautions
Concentrated acids are strongly corrosive to all body tissue, especially eyes and skin. Concentrated acids are highly toxic due to their extreme corrosiveness. Hydrochloric and acetic acids are also toxic by inhalation. Other hazards are presented in this review. Always wear chemical splash goggles, chemical-resistant gloves, and a chemical- resistant apron whenever using concentrated acids or acid solutions.
Purchase
• Purchase dilute acids whenever possible. Dilute acid solutions are safer, and easier to handle, use, and store than concentrated acids. They will also save valuable prep time.
• Purchase small quantities of acids to help keep your acid fresh and to make storage and handling safer and easier. It is easier to clean up a 100-mL than a 2.5-L acid spill.
• Always purchase concentrated acids in PVC-coated glass bottles. PVC-coated bottles will not shatter and spill acid when dropped. The PVC creates a plastic enve- lope around the bottle that greatly reduces spills and breakage. The PVC coating may discolor over time, especially when exposed to hydrochloric acid fumes. This discoloration does not affect the PVC coat- ing or the quality of the acid inside the bottle.
Storage
• Store all acids in a dedicated corrosives or acid cabinet. The best acid cabinets are built with wood because metal cabinets will quickly corrode from acid fumes. Wood cabinets will provide years of safe and
Properties of Acids
durable acid storage. The cabinet should be located in a locked chemical storeroom. If not, the cabinet must be secured with a lock.
• Storing acids and bases together in one corrosives cabinet is acceptable if they are physically separated on different shelves or isolated from one another. Bottles may become covered with ammonium chlo- ride from hydrochloric acid and ammonia fumes. The cabinet and bottles should be washed with TSP (Trisodium phosphate) or other strong cleaners to remove the white film.
• If an acid cabinet in not available, store concentrated acid in Flinn Saf-CubesTM. A Saf-Cube will provide good secondary containment and protection. (See page 122.)
• Label all prepared acid solutions before storing them with at least the name of the acid, concentration, hazard warning or how the acid can hurt you, and date prepared on the label.
• Always keep the appropriate color-coded acid bottle cap on the concentrated acid bottle. Never use these caps on other bottles. Color-coded bottle caps provide an extra safety measure to identify concen- trated acids if the label is removed or destroyed. If an acid bottle cap becomes cracked or discolored, always replace the cap with the proper color-coded cap. The following colors are used on all concen- trated reagent bottles sold in the United States.
• Acetic Acid — Brown
• Phosphoric Acid — White
• Hydrochloric Acid — Blue
• Sulfuric Acid — Yellow
• Nitric Acid — Red
• Ammonium Hydroxide — Green
• Concentrated hydrochloric acid fumes continuously and cannot be stored with- out releasing hydrochloric acid fumes. These fumes are responsible for most of the corrosion damage in your chemical store- room. Storing hydrochloric acid in a wood acid cabinet is a must. Hydrochloric acid
Acid
Formula
F.W. g/mol
Specific Gravity
Concentrated Acid
wt% Acid
Molarity
Acetic
HC2H3O2
60.05
1.05
99.8
17.4
Hydrochloric
HCl
36.46
1.19
37.2
12.1
Nitric
HNO3
63.02
1.42
69.5
15.8
Phosphoric
H3PO4
98.00
1.70
86
14.8
Sulfuric
H2SO4
98.08
1.84
96
18.0