Difference between revisions of "Safe handling and storage of chemicals"

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Storage of many chemicals require additional or special requirements, to avoid hazards as well as contamination. However, manipulating said chemicals does not end with the storage area and handling them safely, during various lab practices, such as purification, distillation, preparation for reaction or simply when moving them around, is equally important.

Storage area guidelines

Storage cabinets and shelves

• Oxidizing acids and flammable solvents must be stored in separate locations.
• Solvents in general must be stored away from any source of heat and light.
• Hazardous materials, especially those that are water sensitive, should not be stored under sinks (except cleaners).^[1]

Corrosive chemicals cabinet

Strong acids are usually stored here

• Such cabinets should either be made from chemical resistant materials or lined with such.
• A double door is recommended.
• Scrubbers are optional, but recommended. An open container of baking soda should take care of acidic vapors.
• Do not store metals or other reducing chemicals in the same cabinet.
• Do not store nitrates and oxochlorine anions in the acids cabinet.
• Amines should also not be stored in the same cabinet as acids, as their fumes will react to form a very fine dust.

Refrigerators

Refrigerators can be used to store volatile substances and to cool exothermic reactions. Although domestic refrigerators can be used to store many chemicals, they are unsuitable for storing corrosive chemicals, such as acids. Several important guidelines:

• Avoid storing acids, as the escaping vapors will corrode the refrigerator.
• Do not store food in the same refrigerator. Do not reuse a chemical refrigerator for food.

Cryonics

• Avoid storing the cryogenic container in light or near a heat source.
• Periodically check the valves.
• Always ensure that cryogenic container has a pressure release valve

Distillation

• Always turn on the cooling first before performing any other operation.
• Ethers and long-chained alcohols must never be distilled to dryness, as they tend form explosive peroxides during storage that can explode when dry.

Containers

• Never store solvents in plastic containers, even those which are supposed to be insoluble in the solvent. One exception is hydrofluoric acid, which cannot be kept in glass, and is generally kept in thick polyethylene or PTFE bottles.
• Periodically open the lids of chemicals which decompose, to allow pressure buildup to release itself. ALWAYS do this when you move a solvent bottle from a cold place to a warm one (some solvents have a very high vapor pressure and can burst if too much pressure builds up inside the reagent bottle).
• Although it is usually not a safety hazard, make sure to store dehydrated chemicals in completely sealed, (usually) glass, containers.

Storage of specific materials

Alkali metals

Lithium

Lithium poses an unusual problem in that it is lighter than almost every single nonpolar organic solvent. The only ones in which it sinks are liquid ethane and methane, which are generally not available or feasible to the amateur chemist. Weighting pieces of lithium down with a heavier metal, such as copper or lead, is common practice. If the metal consists of large or flat pieces, a neat trick is to place a flipped small stainless steel sifter over them. The sieve's weight will hold the lithium chunks at the bottom of the oil container, while allowing the oil to pass through its holes. And since lithium is harder than the other alkali metals, it will not extrude itself through the sifter holes due to its buoyancy. Try using sifters with large holes.

If the bottle can be sealed efficiently, you can also simply flip it upside down, like seen here. This reduces significantly the amount of oxygen that enters the bottle, as oxygen is extremely poorly soluble in mineral oil.

Sodium

Sodium is more reactive than lithium, but it's denser than mineral oil and most organic solvents and can be easily stored for months.

Potassium

Potassium is more reactive than the first two and while it can be stored under mineral oil, it will corrode much faster. Sealing the bottle is recommended. Ampouling is sometimes used.

Rubidium and caesium

Both rubidium and cesium are extremely reactive and even pyrophoric. They can only be stored under mineral oil for short periods, ampouling is used instead.

NaK

Unlike the pure alkali metals, the sodium-potassium mixture, in a 77:23 K-Na ratio, is liquid at standard conditions. It is pyrophoric and less dense than water. It is usually stored under hexane or ampouled, since it's lighter than most organic solvents used to store alkali metals. It will also corrode PTFE.

Ammonium compounds

While ammonium salts of strong acids are stable and can be kept for long periods of time, even in the presence of moisture, the salts of weaker acids will slowly decompose over time, to release ammonia gas, as well as vapors of the said acid (ammonium acetate for example tends to give off a strong vinegar smell over time). This can be limited if the container is kept at low temperatures. Such container should be open periodically, to release the ammonia build-up.

Bases

Alkali bases

Most alkali bases are extremely hygroscopic and will slowly attack glass, and will degrade plastic materials. The also tend to absorb carbon dioxide and sulfur dioxide from air. They should be kept in closed thick bottles, made of PE.

Alkali hydrides will react with both water and air, and must be kept in sealed containers or ampoules.

Alkaline earth bases

Alkaline earth bases are less hygroscopic that their alkali counterparts, but will still react with water and carbon and sulfur dioxides. They can be kept in both plastic and glass containers, as they react much slower with them than the alkali bases.

Alkaline earth hydrides are less reactive that their alkali counterparts, but they still have to be kept in sealed containers, away from moisture and most gasses.

Beryllium

Although beryllium and its compounds have very useful properties in many applications, their toxicity limits their use. Beryllium metal will slowly oxidize in open air to form beryllium oxide, which is easy to scrape off the metal and get airborne. If inhaled, beryllium can cause various illnesses, such as berylliosis. Bulk metal is less prone to releasing toxic dust, but finely powdered beryllium is a greater hazard, and is best to keep it ampouled or in a container with inert gas, to limit oxidation.

Carbides

Calcium carbide

Calcium carbide, like most alkaline earth carbides is sensitive to moisture, and will release acetylene gas in contact with water. Consumer grade CaC₂ also contains traces of calcium phosphide, which in contact with water releases toxic phosphine gas, which gives carbide its bad smell, and may also pose a fire hazard. Always keep the calcium carbide in a closed or sealed container, and absolutely away from moisture.

Ethers

Ethers stored for long periods of time in contact with air will form explosive peroxides, that are a hazard, usually during the distillation, or when opening the storage bottle. Ethers like dimethyl ether, methyl tert-butyl ether or di-tert-butyl ether do not form explosive peroxides, while common ethers, like diethyl ether or THF will slowly form explosive peroxides over the course of several months. Diisopropyl ether tends to form explosive peroxides much easier than the former two, and its use in chemistry is generally avoided. To avoid this unpleasant effect, adding small amounts of an anti-oxidant like BHT (butylated hydroxytoluene), or a clean copper wire will prevent the formation of peroxides. Iron(II) sulfate can also be added to neutralize the peroxides. Sodium hydroxide flakes are generally added to precipitate any forming peroxides. Ethers in general are never distilled to dryness, as ether peroxides tend to explode when dry. Adding dry glycerin may help in keeping the distillation residue wet.

Halogenated carbons

Chloroform

Chloroform will form phosgene over long periods of time, in contact with air and UV light. Keep the chloroform in amber bottles and add a small quantity of ethanol or other preservative to limit the formation of phosgene.

Halogens

Bromine

Bromine is extremely difficult to safely store, as its vapors will escape the storing bottle and corrode most metals and many plastic materials. Sealing the storage bottle with parafilm or PTFE will slow the vapors from escaping, but parafilm will eventually degrade, and needs to be replaced periodically. Ampouling is recommended, though sealing the ampoule is complicated by the volatility of bromine. Unlike iodine vapors, the bromine ones are more toxic, and is recommended that the bottle should be stored in a container with a scrubbing agent, like a thiosulfate salt, inside the storage cabinet.

Iodine

Iodine is notorious for escaping the storage vessel, as well as corroding almost any material, except glass and noble metals. Its vapors will destroy aluminium, severely corrode iron and its alloys and irreversibly stain most plastic materials. Ampouling is recommended, while sealing the bottle with parafilm or PTFE will only slow its escape. Since its vapors aren't as dangerous to health as bromine, simple storing the container in a corrosive cabinet is usually sufficient.

Higher alchols

Alcohols such as isopropanol, butanol, sec-butanol, have been observed to form explosive peroxides upon storage in the presence of air over very long periods of time (usually years), in the absence of an anti-oxidant. Just like in the case of ethers, they have a much higher boiling point than their respective alcohols, and are prone to detonation when dry. Periodically check the alcohols for any signs of peroxides.

Mercury

Mercury is the only liquid metal at room temperature, and as such it can flow from its container in the event of a spill. While the metal itself is relative inert, its vapors pose a hazard if inhaled over a long period of time. Mercury can be stored in glass or plastic bottles, away from certain metals such as aluminium. It is not always necessary to seal the container, but it is recommended to limit the exposure to mercury vapors. The mercury container can also be placed in another, where sulfur powder is added, to absorb its fumes and limit its escape.

Osmium

Bulk osmium is extremely resistant to corrosion and does not oxidize under standard conditions, but fine osmium powder is much more reactive and will slowly oxidize to form the dangerous osmium tetroxide, which has a relative low melting point (40.25 °C) and tends to volatilize easily. The biggest hazard is that it takes a few hours for the poisoning symptoms to appear, so it's difficult to determine the level of exposure. A good tip is to add a gas heavier than air inside the container, like carbon dioxide, sulfur hexafluoride, argon, etc., to limit the oxidation of the osmium powder.

Phosphides

Phosphides, such as aluminium phosphide are, just like group II carbides, sensitive to water. The reaction of phosphides with water releases the extremely toxic phosphine gas, which in sufficient quantity may cause death. Always keep the phosphide in an air-tight sealed container, in a plastic bag to limit the moisture. It's also recommended to keep it very safe (or not experiment with it at all), as the phosphine smell is usually associated with meth labs, and you may not want the police to pay you a visit in case of a leak.

Volatile chemicals

Unless you're perfectly sealing the containers, volatile chemicals such as volatile solvents will eventually escape the bottle. While you can seal the bottles with tape to limit the evaporation, you must make sure the reagents are kept at low temperatures if stored for long periods of time.

Chemical compounds with a boiling point between the freezing point of water and room temperature should either be kept in a freezer, or in a gas cylinder under pressure, while compounds with a boiling point lower than the freezing point of water must always be kept in a gas cylinder.

White phosphorus

White phosphorus should be tightly sealed in an extremely durable container, away from light to prevent degradation. WP can be safely stored underwater. Always check the water lever, to make sure the phosphorus is not exposed to air.

Handling

Acids

Hydrofluoric acid

Hydrofluoric acid should never be kept or handled in glass containers (e.g. beakers), because of its ability to dissolve (most) oxides and silicates. It should be handled in thick plastic containers. It should only be handled in a fume hood, or gloveboxes. Nitrile gloves are not very useful at concentrations higher than 30%. For concentrations between 30-70%, butyl rubber and neoprene gloves offer protection for at least 4 hours, where as for concentrations higher than 70%, gloves made of neoprene rubber, Barrier® (PE/PA/PE), Trellchem® HPS or Tychem® TK will offer protection for a same time period.^[2] Always use thick gloves, never thin. A good tip is to wear two pairs of gloves at a time, changing the outer pair after a few uses. NEVER use natural rubber, as HF readily penetrates it. For body protection, always wear a long-sleeved lab coat and chemical-resistant apron over long-sleeved shirt, long pants, and closed shoes. Goggles, along with a face shield or a mask should be worn as face protection. A neutralizing agent such as sodium bicarbonate or calcium carbonate should be kept near the working stand. An antidote, like calcium gluconate should be kept close in the event of an accident.

Perchloric acid

The maximum concentration at which perchloric acid can be safely stored is 70%. As it is a very powerful oxidizer, all the glassware where is about to be poured in should be inspected for any organic traces. The storage containers and beakers should be perfectly cleaned and dry. While experiments with perchloric acid can be performed outside, there is a risk of contaminating both the acid and glassware with organic materials such as dust, insects or other particulates, especially when working at high concentrations. Gloveboxes are not entirely suitable, as the closed environment may allow the build-up of dangerous perchloric acid vapors. If you have the skills, you may be able to construct a washing system to flush out the acid vapors and safely neutralize them. Specially designed fume hoods with wash down systems are generally preferred when working with perchloric acid. These fume hoods are lined with PVC or 316 type stainless steel and have a wash down system than removes the perchloric acid vapors, which are drained to labeled waste containers.

Incompatible chemicals

References

1. ↑ http://www2.lbl.gov/ehs/chsp/html/storage.shtml
2. ↑ http://chemistry.harvard.edu/files/chemistry/files/safe_use_of_hf_0.pdf
3. ↑ http://ccc.chem.pitt.edu/wipf/Web/Chemical_Incompatibilities.pdf