5. Things to Know for Upper-Class Chemistry Students

5.1 Self-Protection

Safety Goggles and Shoes: As always, safety goggles and closed-toe shoes must always be worn in the lab. Remember to tie back long hair.

• For Lasers: Special precautions are necessary, and special goggles are available for use. Consult your instructor.
• For Glassblowing: Use didymium glasses that reduce the glare from glowing glass. The light from the high temperature glass can damage your eyes very quickly, so NEVER look at it without didymium glasses (and a smile on your face).

Fume Hoods: All work that involves organic compounds, toxic materials, or malodorous compounds should be carried out in the fume hood. The environmental health and safety staff analyzes hoods for performance in terms of air velocity at the mouth or intake point, and exhaust volume of air in cubic feet per minute. Do not override or disable mechanical stops on the sash. Do not push the sash above the lock position nor place items in the front six inches of the hood, as this diminishes exhaust capabilities. Never place your head inside the hood.

Be sure to turn on the fan any time you use a hood. If a hood is not working properly (for example, if the door does not close in position or if the fan motor is not operational), students should tell their instructor AT ONCE. Proper ventilation can make the difference between a safe working environment and a dangerous or toxic one.

5.2 Waste Disposal

• Minimize mixing hazardous waste with non-hazardous waste, such as water. Do not dilute hazardous waste. This not only increases the volume necessary for disposal, but may also affect any reusable properties of the waste, such as British Thermal Unit (BTU)/heat value. The only exception is adding water to explosive chemicals to keep them wet.
• Segregate your waste according to waste streams, such as organic solvent waste (no water), photo fixer waste, aqueous waste with organic solvents, aqueous waste with toxic heavy metals, aqueous acidic waste, aqueous basic waste, metallic mercury waste, lubricating oil, formalin, or ethidium bromide.
• Use only compatible containers for collecting waste.
• Label all containers to prevent the generation of “unknowns.” Label all stock, transfer, and waste containers appropriately. All containers must show:

• The chemical name in English. It may never be abbreviated.
• Approximate concentrations for each component in a mixture
• The hazards associated with the chemical
• Generator information that includes your name, phone number, the date, and your department

Failure to label the contents of containers can result in very expensive disposal costs since unlabeled containers require special analytical or “fingerprinting” procedures to determine appropriate classification and disposal methods.

• Ensure that containers are in good condition, closed at all times, stored in bins or trays, adequately segregated, and inspected regularly.
• Avoid contamination of stock chemicals
• Keep in mind that Reed College retains permanent liability for the management and appropriate disposal of your waste. As a means of ensuring compliance with the law, the DEQ and EPA may perform unannounced inspections at any time. Operations that do not meet regulatory requirements can result in substantial penalties, including fines of up to $25,000, per day, per violation. Over the past few years numerous universities and colleges have been fined millions of dollars for violating hazardous waste requirements.

Sharps: Sometimes you will use hypodermic needles and syringes during chemical analysis or other work. Place disposable needles in red plastic "biohazard" containers, never in the trash. Consult the stockroom manager for the location of these containers.

Listed Toxic Wastes (among others): The following, among others, cannot go down the sink: cyanides, sulfides, azides, and atrazine. Your lab instructor will provide a container in which to dump these wastes, and the environmental health and safety personnel will take care of their disposal.

Chemistry often makes use of methods involving radiation or radioactivity. Reed has facilities for X-ray diffraction (inorganic chemistry), X-ray fluorescence, gamma-ray spectrometry (analytical), and liquid scintillation counting. Radioactive materials may be prepared using the Reed reactor facility or purchased from commercial suppliers following approval by the radiation safety officer. Always adhere to established safety procedures in all experiments involving radiation-emitting equipment or radioactive materials (see instructor[s] in charge of such equipment). All work involving radioactivity or radiation comes under Reed College’s license from the State of Oregon Department of Health, radiation control section. At Reed, the radiation safety officer (RSO) and the radioactive materials committee (RAM), reporting to the president of the college, administer this license. Because one license covers all activities at Reed (except for the nuclear reactor, which has a Nuclear Regulatory Commission license), all uses involving radiation or radioactive materials must have prior authorization from the RAM committee.

Any student using radioactive materials, or radiation-emitting equipment, must receive training and pass an examination in radiation safety procedures from the RSO, before commencing experimentation. The RSO reviews all proposed purchases of radioactive materials, ascertains that the experimenters are qualified for safety, and ensures that the purchase is permitted under the radioactivity license granted to Reed by the State of Oregon. Address any questions concerning work with radioisotopes or radiation-emitting equipment to the RAM, RSO, or the faculty member authorized to use the equipment. You can reach the RAM or the RSO through the office of the reactor director or the environmental health and safety office.

5.4 Laser Safety: Class IV-High Power Laser

Invisible Laser Radiation: Because the 1064 nm output of a Nd:YAG laser is invisible, it is extremely dangerous. Infrared radiation passes easily through the cornea, which focuses it on the retina, where it can cause instantaneous permanent damage. Some precautions for the operation of Class IV-high power lasers:

• Keep the protective cover on the laser head at all times.
• Avoid looking at the output beam: even diffuse reflections are hazardous.
• Avoid wearing reflective jewelry while using the laser.
• Use protective eyewear at all times; selection depends on the wavelength and intensity of the radiation, the conditions of use, and the visual function required. For UV light, basic plastic safety goggles are sufficient.
• Expand the beam wherever possible to reduce beam intensity.
• Avoid blocking the output beam or its reflection with any part of the body.
• Establish a controlled access area for laser operation. Limit access to those trained in the principles of laser safety.
• Maintain a high ambient light level in the laser operation area so the pupils of the eyes remain constricted, reducing the possibility of damage.
• Post prominent warning signs near the laser operation area.
• Set up experiments so the laser beam is either above or below eye level.
• Provide enclosures for beam paths whenever possible.
• Set up shields to prevent unnecessary specular reflections.
• Set up an energy-absorbing target to capture the laser beam, preventing unnecessary reflections or scattering.

5.5 Dealing with Tanks of Compressed or Liquefied Gas

When dealing with tanks of compressed or liquefied gas, remember to:

Securely fasten all gas tanks, functioning at floor level, in position with a strap and a device anchored to the edge of the bench. The pressure inside the most commonly used gas tanks (oxygen, nitrogen) is so high (about 200 atmospheres) that enormous damage can be done if they are knocked over and cracked (they will become random rockets). Only those people who are experienced in moving gas cylinders may transport a gas cylinder from one location to another, and then, only with the use of a special cradle and straps. The gas tanks are usually heavy, large, and very unwieldy. The uninitiated can easily be surprised and maneuvered into a dangerous situation. Before moving a tank, remove the regulator and replace the protective cap.

Refer to the manufacturer’s catalog (usually the Matheson Co.) to determine the appropriate type of regulator for a particular gas tank. Some regulators (such as those for hydrogen) are made with left-handed screw threads. Some regulators are made of special corrosion-resisting alloys (for example, HCl, HBr, Chlorine, NO2), and others are fitted with dials. Simple ones are not. Never try to fit a regulator to a tank without first checking with your instructor or with the stockroom manager. Never use any lubricant on a high-pressure oxygen regulator; it will explode. Use a paintbrush to easily check seals. Dip the paintbrush in mildly soapy water. "Paint" onto areas where leak is suspected or likely. Check for bubbles.

Always use a well-ventilated hood if your gas tank contains toxic or corrosive gases.

5.6 Low Pressure—Vacuum Systems

The main concern of low-pressure work is that certain vessels may implode and shatter when evacuated. Although spherical flasks resist external pressure changes best because the stress is equally applied, the same does not apply to Erlenmeyer flasks, which implode when evacuated. Always inspect your glassware for small cracks and etched lines before using in the laboratory.

Considerable risk is associated with the evacuation of large vessels. Round-bottom flasks larger than one liter should not be evacuated (they are not thick enough). Desiccators that are evacuable ("vacuum desiccators") are made of especially thick glass, including flanges that must be well greased and/or fitted with O rings.

Exercise great care in handling Dewar flasks and other evacuated vessels. These are normally taped to provide protection in case of implosion. You should wear eye protection when handling Dewars.

5.7 Peroxide Issues

Since ethers and alcohols are among the most commonly used organic solvents, their reaction with oxygen in the air deserves special attention.

Diethyl ether, the most commonly used ether, is supplied in two major grades. Commercial, which contains water and ethanol, is the grade to be used for most extractions. Anhydrous diethyl ether is supplied in sealed cans and contains a small amount of "stabilizing" agent—that is, a compound that reacts rapidly with the initial free radicals formed by reaction with oxygen and hence eliminates the autocatalytic effect. Because this stabilizer is present in a very small amount, it does not provide long-term protection against peroxide formation once someone opens the can.

In addition to diethyl ether, other commonly used ethers and alcohols are dioxane, tetrahydrofuran, di-isopropyl ether, glyme (the dimethyl ether of ethylene glycol), diglyme, triglyme, 2-butanol, 2-octanol, and cyclohexanol. All of these ethers form peroxides and should be used with the following precautions:

• All containers for these ethers and alcohols should remain well sealed when not in use. Particularly in the case of the more volatile ether or alcohol, a loose stopper allows both a slow evaporation and reaction with oxygen. Consequently, the peroxides gradually accumulate in the residue as the volume declines.
• If, at any point in the use of an ether or alcohol, you intend to distill the ether or alcohol you must test for peroxide content before the distillation (see below).
• Date all containers upon opening, as old containers with high peroxide content may explode.

Open containers will be tested or discarded yearly once opened.

Tests for peroxides and their removal

Peroxides can be detected by shaking a sample of the ether or alcohol with a freshly prepared solution of KI (5 to 10%) which has been acidified by the addition of a few drops of hydrochloric acid. The appearance of a yellow or brown color due to I2 signifies the presence of peroxides.

In order to prepare completely anhydrous and peroxide-free ethers and alcohols, the samples should be obtained initially from freshly opened, highly purified solvents (JT Baker or Burdick and Jackson), placed in a distillation flask under a blanket of N2 (do not continue passing N2 into the system once the blanket has been established—consult your instructor on the appropriate set-up) followed by the addition of benzophenone and sodium shavings.

The sodium ketyl of benzophenone has a brilliant blue color, and as long as this color is present, there can be no moisture or peroxide in the solvent directly distilled from this solution as needed. Leave the remaining solution for a future distillation.

Peroxide test paper is available in the stockroom. See the stockroom manager for more information.

A note about biological extractions: Those who use ether or alcohol for the extraction of biological materials must be particularly careful. There is danger that nothing was extracted and that only the peroxide remains to explode on evaporation. Generally, if other organic material is present, the peroxide will not explode—it will simply destroy some of this material rather than detonate.

A List of some Peroxidizable Compounds

5.8 Flammability

Information about the fire hazards of various chemicals may be found in The Chemists’ Companion, A.J. Gordon and R.A. Ford (John Wiley & Sons, New York, 1972), pages 510–513, on reserve for Chemistry 210. In particular, notice the columns headed "Flash Point" and "Ignition Temperature." The "Flash Point" is the minimum temperature at which the vapors ignite and initiate continuous burning of the liquid or solid when in contact with sparks, flames, or other ignition sources. The "Ignition Temperature" is the temperature (in °F) at which the material will spontaneously inflame in air. Give special attention to those compounds with ignition temperatures less than 500°F. Their vapors will readily ignite on contact with any moderately hot surface, such as that of a hot plate, or by allowing air into any distillation system which has been heated to 200° to 250°C (a not uncommon temperature).

In addition, some cases call for special attention: CS2 will ignite at 212°F or 100°C, and its vapor may ignite at a warm room temperature, 86°F. Hence, keep it under water.

Notice also the low flash points for commonly used solvents such as acetone, 0°F; dioxane, 54°F; diethyl ether, -49°F; ethyl alcohol, 55°F; n-hexane, -7°F (typical of gasoline); toluene, 40°F. This means that the slightest spark from a stirring motor or hot plate control switch is sufficient to initiate a fire at room temperature for such solvents.

Another property related to fire and explosion hazards in the handling of chemicals is the percent by volume, which is flammable in a vapor/air mixture. This information is also in the Chemists’ Companion reference. You will notice that even very low percent of vapor in the air supports burning or explosive combustion. Many substances will support combustion in as little as 1 to 5% concentrations in air. Additional information in this property is to be found in the "CRC Handbook of Chemistry and Physics," Section D, under the heading "Limits of Inflammability." Note in particular the wide ranges for hydrogen, acetylene, ethylene oxide, carbon monoxide, acetaldehyde, and carbon disulfide.

In summary, since the majority of organic liquids have flash points at or below room temperature and are flammable at a very low concentration in air, the safest procedures are those that avoid contact between organic vapor and any sources of sparks or flame. All organic compounds that are liquid at room temperature give vapors whose density is greater than air. In order to minimize flammability hazards you must observe the following precautions:

• Before pouring any volatile liquid (b.p. less than 150°C), inspect the bench area for flames or for hot plates turned on, even if only for stirring. The more volatile the liquid, the farther away the "foreign" hot plate must be. For low boiling flammable liquids such as acetone, diethyl ether, and pentane, at least six to eight feet of bench space should intervene, since the vapors will flow along the desktop. If an aisle intervenes, the distance may be somewhat less for the transfer of small quantities. Large-scale transfers involving hundreds of milliliters should occur only in a hood and with no flames or hot plate turned on in the hood area.
• Your lab is equipped with steambaths, silicone oil baths for use on hot plates, and heating mantles to use as heating sources. Do not use Bunsen burners, except in unusual circumstances, even though you will find that laboratory directions occasionally call for their use. Older, less well-equipped labs had to use Bunsen burners since there were no alternatives.
• Before opening any system containing hot organic vapors, turn off the hot plate that has supplied the heat. Also, because of the spontaneous ignition problem cited above, never allow air into a system containing organic vapors above 150°C. For example, mixtures of air with dioxane and ethyl ether will ignite explosively above 185°C. Normally such compounds will not be present at this temperature; however, serious explosions have been reported in systems that were at 200°C in a vacuum and were generating dioxane by a decomposition process.

5.9 Detonation

Detonation may occur whenever an exothermic reaction with low activation energy generates gaseous products. In some cases, such as with acetylene, azides, and diazomethane, unstable molecules rearrange to give more stable molecules, such as graphite, H2, and N2. In a large number of examples, detonation is the consequence of a redox reaction occurring between molecules such as H2 + O2, or Cl2 + CH4; or, as in the case of explosives such as nitroglycerine and other organic nitrates, by "internal" redox reactions. The following compounds are representative of those for which special precautions are necessary:

• Compounds containing several nitrogen atoms linked, especially by multiple bonds, such as azo compounds (except azobenzene and related aromatics), diazonium salts, azides, triazenes, and tetrazenes.
• Diazomethane is a particularly dangerous substance since it is both very toxic and unpredictably and violently explosive.
• All organic derivatives of hydrogen peroxide, such as peroxides (ROOR), hydroperoxides (ROOH), peracids [RCO (OOH)], and diacyl or diaryl peroxides (R-CO-O)2.
• Fulminates (salts of HONC) and heavy metal salts of acetylene.
• Any organic ester of a strongly oxidizing acid such as nitric, chromic, perchloric, and permanganic.

5.10 Skin Contamination; Protective Clothing

The skin is a very sensitive organ that can be adversely affected and permanently damaged by some chemicals. Inform your instructor and your dermatologist immediately in case of injury. The most common injuries to the skin include:

• Cuts: from broken glass (tubing, broken thermometers, damaged glass vessels), from the edges of paper sheets, from sharp metal edges and points, and from abrasions. First aid: wash wound with water and stop bleeding, if any. Tell the lab instructor.
• Chemical Hazards: The following compounds are the ones you will most likely encounter in ordinary laboratory work. They also represent members of larger classes of compounds with similar properties. As you become more familiar with chemicals, you need to develop an understanding of those chemical and physical properties that create hazard. In this way, you can anticipate potential hazards when you encounter chemicals not specifically listed here.
• Thermal burns: burns from hot objects.
• Corrosive burns: from acids, alkalis, some salts, compounds which react avidly with water (such as acid halides, anhydrides such as phosphorus pentoxide), some oxidizing agents (hydrogen peroxide).
• Attack by vesicants (blistering agents) such as bromoketones, mustard gas (ClCH2CH2)2S, and analogous chemicals.
• Frostbite: from handling dry ice (-80°C) or cryogenic liquids.
• Allergic reactions: such as rashes resulting from contact with certain phenols (poison oak or poison ivy constituents) and other types of chemicals for which students may have individual susceptibility.

In general, you can do a great deal to minimize these dangers. Gloves provide good protection for most problems associated with hands. Students should take care to select the proper protective gloves that are appropriate to the hazard. You can get assistance in glove selection from the class instructor or the environmental health and safety office (ext. 7788). No single type of glove will protect you from all hazards. Thin gloves, such as the blue nitrile gloves used in most labs, provide protection from many common chemicals and give the best tactile sensation, but are easily punctured. Thick rubber gloves afford good protection from the more corrosive and penetrating chemicals like acids, but give poor tactile sensation and can be slippery. Make sure that you examine gloves for holes or discoloration before use. It is urged that you wash your hands, with the gloves on, before removing them. This will decrease the likelihood of contaminating yourself or others while your gloves are being removed and disposed of. An appendix shows the resistance of some common glove materials to various chemical classes.

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