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HANDLING LIQUIDS. OBTAINING THE CHEMICAL. Take an appropriate container to the reagent shelf. Avoid measuring volumes of strong acids and alkaline solutions with your graduated cylinder held at eye level. Support your graduated cylinder on your bench; add hazardous liquids a little at a time, inspecting after each addition. REAGENT IN A DROPPER BOTTLE. If the general supply bottle is equipped with a dropper, use it, but be sure that the dropper never touches your container or the contents in it. Never put it down on the bench top, but return it immediately the right reagent bottle. REAGENT IN A STOPPER BOTTLE. If the general supply bottle is equipped with a stopper, the stopper should either be held during the transfer or placed on its flat top. Do not lay the stopper on its side on the bench top. Pour chemicals from the general supply bottle into your container. Be sure that the proper stopper is returned to the supply bottle; do not interchange stoppers. MIXING. If liquid chemicals are to be mixed with water, always add the concentrated chemical to water rather than the other way around. This keeps the new solution dilute at all times and avoids many accidents. Usually addition should be done slowly, using small quantities. It is especially important to add acid to water because of the heat generated. PIPETTING. Liquids are drawn into the pipet by applying a slight vacuum at the top, using a small rubber suction bulb but NEVER THE MOUTH. HEATING. Liquids in beakers and flasks can be heated by placing them on a ring stand on wire gauze with the container supported by a clamp. Liquid should never be heated in a graduated cylinder or in other columetric glassware. DISPOSAL. Check with your laboratory instructor before disposing of any chemicals down the drain. If the liquid chemical can be disposed of in the skin, dispose of it by rinsing it down the sink with large quantities of water. Avoid unnecessary splashing during this process by pouring the chemical directly down the drain while the water is running vigorously. HANDLING SOLIDS: THE CONTAINER. Take an appropriate container to the reagent shelf where the general supply is kept. Solids are somewhat more difficult to transfer than are liquids, so a wide-mouthed container such as a beaker is preferable. THE TRANSFER. During the transfer, hold the stopper or lay it on the bench without contaminating the stopper. Solid chemicals are most easily poured by tipping the general supply bottle and slowly rotating it back and forth. Mere tipping of the bottle alone often causes large chunks to come out very suddenly which leads to spills. If you use your own spatula, be sure that it is absolutely clean. Return the proper stopper to the general supply bottle; do not interchange stoppers. MIXING. If the solid is to be mixed with a liquid, add the solid to the liquid. Additions should be made in small quantities except in special circumstances. DISPOSAL. If the laboratory instructor directs you to dispose of any solid chemicals in the skin, flush it down the drain with copious amounts of running water. All other solids should be disposed of in special containers provided for this purpose. IF AN ACCIDENT OCCURS........ In spite of the best efforts of all concerned, accidents sometimes occur in the laboratory. Use good judgment and do not panic in case of an emergency. Enzymes are biomolecules that catalyze (i.e., increase the rates of) chemical reactions.[1][2] Nearly all known enzymes are proteins. However, certain RNA molecules can be effective biocatalysts too. These RNA molecules have come to be known as ribozymes.[3] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell. Like all catalysts, enzymes work by lowering the activation energy (Ea or ΔG‡) for a reaction, thus dramatically increasing the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions.[4] A few RNA molecules called ribozymes catalyze reactions, with an important example being some parts of the ribosome.[5][6] Synthetic molecules called artificial enzymes also display enzyme-like catalysis.[7] Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g., pH), and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics. In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew).