CHEMICAL MANAGEMENT: INSPECTIONS, STORAGE, WASTES, AND SECURITY

MANAGING CHEMICAL hazards is an important and necessary skill for chemists. A chemical analysis or synthesis is one part of the process of doing chemistry. Before an experiment is done, chemicals have to be safely purchased and stored, and afterwards the products of an analysis or reaction need to be handled in a safe and environmentally responsible fashion.

Strong acids and strong bases react, and oxidants and reductants react Strong acids and strong bases react, and oxidants and reductants react. So, just because a chemical is “safe” by itself in water, doesn’t mean it won’t react with something else. Some particularly wellknown examples of “never down the sink” chemicals are salts of azides (N3-) and perchlorates (ClO4-) that can form explosive compounds with metal cations. Sulfides (S2-) and cyanides (CN) will form poisonous gases in contact with acids. (It is not likely that you’ll encounter these anions in introductory courses.) And it is never wise to put a solid into a sink. Anything that is insoluble in water will end up sitting in the trap, just waiting for a chemical with which it will react.

Disposing of a solid chemical into a common task receptacle is almost never wise, unless specifically told to do so. It is possible, but perhaps not likely, that the chemical will react with something else, but since custodians often reach into wastepaper baskets to simply remove trash—although it is always wiser not to do so—it is possible that someone could be injured or contaminated by the solid.

The first and simplest rule about handling laboratory wastes is: Don’t put anything into a trash can or down the sink unless specifically instructed to do so. While “down the sink” is almost never appropriate in research labs, in fact in introductory chemistry classes there are some solutions that can be poured down the sink and the occasional solid product that can be placed in a trash can. Introductory lab experiments are often designed to use and produce innocuous chemicals since (1) the chemical principles that are being taught can be accomplished using these “safer” chemicals, (2) not having to further handle the chemical wastes saves time for stockroom personnel, and (3) this saves money by not having to pay to dispose of chemicals wastes.

However, introductory lab courses will also inevitably generate many wastes that cannot be poured down a sink or placed in a trash can. There are three main reasons why we should be mindful of appropriate waste disposal: environmental protection, safety, and cost. To minimize waste disposal costs, it is imperative that all wastes first be clearly identified. The most expensive waste to dispose of is always the “unknown” waste since it must be treated as if it is extremely hazardous until testing has proved otherwise. And the cost of this kind of testing is high, which drives up the cost of disposal.

GENERAL GUIDELINES There are many other features of the general topic of waste disposal that needn’t concern you as a student but are very important in the chemical industry for both manufacturing and research facilities. The first and most important rule is: Follow instructions! It is easy at the end of a lab experiment to be rushing to finish the experiment, clean and put away equipment, and move on to the next task in your academic life. And it is usually at the end of the experiment when you are likely to take care of accumulated wastes. So, take a little time to be conscientious about this task for reasons of safety, environmental protection, and cost savings

Don’t pour anything down the sink unless you are instructed to do so Don’t pour anything down the sink unless you are instructed to do so. Some solutions can be poured down the sink and some solids can be placed in an ordinary trash can, but this determination will be made by your instructor, not you. Most wastes will have specific waste jars available to receive them. Read labels carefully. If you inadvertently dispose of a chemical in the wrong receptacle, tell your instructor! Not telling your instructor about this kind of mistake can lead to a serious incident due to an unexpected reaction in the waste jar or some reaction in subsequent steps when the waste is processed. •Anything that becomes contaminated with a chemical, including paper towels, sponges, or ordinary paper, must be treated separately. Ask your instructor what to do.

Broken glassware that is contaminated with any chemical must similarly be handled by someone else. Ordinary glassware that is broken and clean should be placed in a special receptacle for broken glass. Handling broken glass can be dangerous and it is best to have a teaching assistant or instructor take care of broken glass. Don’t mix wastes unless specifically told to do so. There are some situations where this is both safe and no more costly than separated wastes. However, “unmixing” chemicals is generally expensive and sometimes quite difficult. All of the steps above assume that you know what the waste is! To be certain about this, all beakers, test tubes, and other containers must always be identified at all times during an experiment with accurate labels. It is easy, at first, to think that you’ll remember what is in each of a few beakers as an experiment proceeds, but this is a system that will inevitably fail. Many solutions are clear and therefore indistinguishable.