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Lab Safety & Basic techniques

Lab Safety & Basic techniques - Safety in the...

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Unformatted text preview: Safety in the Chemistry Laboratory Everyone who works in a chemistry laboratory should follow these safety precautions. 1. Wear safety goggles and a laboratory apron in the laboratory at all times. 2. Shoes must be worn in the laboratory. Avoid wearing overly bulky or loose fitting clothing. Remove any dangling jewelry. 3. Conduct only assigned experiments, and do them only when your teacher is present. 4. Know the locations of safety equipment such as eyewash fountains, fire extinguishers, emergency shower, and fire blanket. Be sure you know how to use the equipment. 5. Do not chew gum, eat, or drink in the laboratory. Never taste any chemicals. Keep your hands away from your face when working with chemicals. 6. Wash your hands with soap and water at the end of each laboratory exercise. 7. Read all of the directions for a laboratory procedure before proceeding with the first part. Reread each instruction before you do it. 8. Notify your teacher immediately if any chemicals, such as concen- trated acid or base, are spilled. 9. Report all accidents , no matter how slight, to the teacher immediately. 10. Pin or tie back long hair and roll up loose sleeves when working with flames. 11. Do not leave a lighted burner unattended. 12. Use a hot plate instead of an open flame whenever a flammable liquid is present. 13. Read the label on a reagent bottle carefully before using the chemical. After removing the chemical from the bottle, check to make sure that it is the correct chemical for that procedure. 14. To avoid contamination, do not return unused chemicals to a reagent bottle. Similarly, never put a pipet, spatula, or dropper into a reagent bottle. Instead, pour some of the reagent into a small clean beaker and use that as your supply. 15. Do not use chipped or cracked glassware. Discard it according to your teacher’s instructions. 16. When diluting an acid, always pour the acid slowly into water with stirring to dissipate the heat generated. CAUTION: Never pour water into a concentrated acid. 17. When heating a liquid in a test tube, turn the mouth of the test tube away from yourself and others. 18. Clean up spills and broken glass immediately. Leave your work area clean at the end of the laboratory period. Safety in the Chemistry Laboratory 5 i .l r 3 6 Laboratory Hazards Laboratory Hazards You should be aware of possible hazards in the laboratory and take the appropriate safety precautions. By doing so, the risks of doing chemistry can be minimized. This safety section is intended to acquaint you with the hazards that exist in the laboratory and to indicate how you can avoid these hazards. In addition, information is provided on what to do if an accident should occur. Thermal Burns A thermal burn can occur if you touch hot equipment or come too close to an open flame. You can prevent thermal burns by being aware that hot and cold equipment look the same. If a gas burner or hot plate has been used, some of the equipment nearby may be hot. Hold your hand near an item to feel for heat before touching it. Treat a thermal burn by immediately applying cold running water to the burned area. Continue applying the cold water until the pain is reduced. This usually takes several minutes. In addition to reducing pain, cooling the burned area also serves to speed the healing process. Greases and oils should not be used to treat burns because they tend to trap heat. Medical assistance should be sought for any serious burn. Notify your teacher immediately if you are burned. Chemical Burns A chemical burn occurs when the skin or a mucous membrane is damaged by contact with a substance. The Materials section of each exercise indi- cates which substances can cause chemical burns. [El stands for corrosive. It indicates that the chemical can cause severe burns. |I| stands for irritant. It indicates that the chemical can irritate the skin and the membranes of the eye, nose, throat, and lungs. Chemicals that are marked [E or [II should be treated with special care. Chemical burns can be severe. Per- manent damage to mucous membranes can occur despite the best efforts to rinse a chemical from the affected area. The best defense against chemical burns is prevention. Without exception, wear safety goggles during all phases of the laboratory period—even during clean-up. Should any chemical splash in your eye, immediately use a continuous flow of running water to flush your eye for a period of 20 minutes. Call for help. If you wear contact lenses, remove them immediately. This is especially crucial if the chemical in— volved is an acid or base. It can concentrate under the lens and cause extensive damage. Wear a laboratory apron and close-toed shoes (no sandals) to protect other areas of your body. If corrosive chemicals should contact your exposed skin, wash the affected area with water for several minutes. An additional burn hazard exists when concentrated acids or bases are mixed with water. The heat released in mixing these chemicals with water can cause the mixture to boil, spattering corrosive chemical. The heat can also cause nonpyrex containers to break, spilling corrosive chemical. To avoid these hazards, follow these instructions: Always add acid or base to water, very slowly and with stirring, never the reverse. One way to remember this critical advice is to think of the phrase, “pouring acid into water is doing what you ought-er”. Cuts from Gloss Cuts occur most often when thermometers or pieces of glass tubing are forced into rubber stoppers. Prevent cuts by using the correct technique for this procedure. The hole should be lubricated with glycerol or water to facilitate the movement of the glass tubing. The glass should not be gripped directly with the hands, but rather, by means of paper towels. The towels will protect your hands if the glass should break. Use a gentle twisting motion to move the tube smoothly into the stopper. Avoid cuts from other sources by discarding chipped and cracked glassware according to your teacher’s instructions. If you should receive a minor cut, allow it to bleed for a short time. Wash the injured area under cold running water, and notify your teacher. Serious cuts and deep puncture wounds require immediate medical help. Notify your teaCher immediately. While waiting for assistance, control the bleeding by apply- ing pressure with the finger tips or by firmly pressing with a clean towel or gauze. Fire A fire may occur if chemicals are mixed improperly or if flammable materials come too close to a burner flame or hot plate. When using this equipment, prevent fires by tying back long hair and loose fitting clothing. Do not use a burner when flammable chemicals are present. These chem- icals are designated with the symbol IE] in the materials section for each exercise. Use a hot plate as a heat source instead of a burner when flammable chemicals are present. I , If hair or clothing should catch fire, DO NOT run, because running fans a fire. Drop to the floor and roll slowly to smother the flames. Shout for help. If another person is the victim, get a fire blanket to smother the flames; If a shower is nearby, help the victim to use it. In case of a fire on a laboratory bench, turn off all accessible gas outlets and unplug all accessible appliances. A fire in a container may be put out by covering the container with a nonflammable object. It could also be smothered by covering the burning object with a damp cloth. If not, call for a fire extinguisher. Spray the base of the fire with foam from the extinguisher. Caution: Never direct the jet of a fire extinguisher into a person’s face. Use a fire blanket instead. If a fire is not extinguished quickly, leave the laboratory. Crawl to the door if necessary to avoid the smoke. Do not return to the laboratory. Poisoning Many of the chemicals used in the experiments in this manual are toxic. Such chemicals are identified in the materials sections with the symbol . You should do several things to prevent poisoning. Never eat, chew gum or drink in the laboratory. Do not touch chemicals. Clean up spills. Keep your hands away from your face. In this way you will prevent chemicals from reaching your hands, mouth, nose or eyes. In some cases, the detection of an odor is used to indicate that a chemical reaction has taken place. It is important to note, however, that many gases are toxic when inhaled. If you must detect an odor, use your hand to waft some of the gas toward your nose. Sniff the gas instead of taking a deep breath. This will minimize the amount of gas sampled. Laboratory Hazards 7 .‘ y i l i: Safety Symbols Take appropriate precautions whenever any of these safety symbols ap— pears next to the instructions in a procedure. Eye Hazard ‘\ 2‘: Inhalation Hazard 0 Wear Safety goggleS. U ' AVOid inhaling :1 substance. (E1 fl Corrosive Substance % Hazard mm M Thermal Burn Hazard . WeaI safety goggles 8:. - Do not touch hot equip- and laboratory apron. ment. ° Do not touch chemicals. v67 Breakage Hazard Fire Hazard y $ ' Do not use chipped or ' Tie back hair and loose CraCked glassware. clothing, ° Do not heat the bottom I la - Do not use a burner near Of a test tube. flammable materials. ; / Disposal Hazard @ Poison Hazard ° Dispose of this chemical ' Do not chew gum, drink, only as direCted- or eat in the laboratory. - Keep your hands away from your face. @ Emergency Procedures Report any injury, accident, or spill to your teacher immediately. Know the location of the closest eye wash, fountain, fire blanket, fire extin- guisher, and shower. Situation Safe Response Burns Immediately flush with cold water until the burning sensation subsides. Fainting Provide fresh air (for instance, open a window). Move the person so that the head is lower than the rest of the body. If breathing stops, use artificial resuscitation. Fire Turn off all gas outlets. Unplug all appliances. Use a fire blanket or fire extinguisher to smother the fire. Caution: Do not cut off a person’s air supply. Eye Injury Immediately flush the eye with running water. Remove contact lenses. Do not allow the eye to be rubbed if a foreign object is present in the eye. Minor Cuts Allow to bleed briefly. Wash with soap and water. Poisoning Note what substance was responsible. Alert teacher immediately. Spills on skin Flush with water. 8 Safety Symbols Student Equipment At the beginning and end of the year, record how many of each item are in your equipment drawer. _ _— _— _— _- _— _— _— _— __— __— __— __— __— __— __— __— __— — — — _ _ — Laboratory Equipment 9 Laboratory Equipment Mortar and ’— pestle ‘1/ Crucible and cover Beaker Florence Wide-mouth Plastic wash Dropper flask collecting bottle pipet bottle E—b Glass rod with nichrome wires (for flame testing) Test tube holder Crucible tongs Metal spatula gm“)? w nut-24mg”: um. Marius-ink Test tube brush Ceramic square \‘V‘ 5‘Z\ '1 \\\\' {i\\\s\ Triangular file amjm ' ram-c: ‘.\-t€ .23?» n: I‘ _\\\\\\t\\\\\\\\\\\\\\\\\\\\\\\\\\\ ? n l ‘ Funnel Erlenmeyer Rubber stoppers flask Scoopula Clay triangle Watch glass Evaporating dish Pneumatic trough Rubber tubing Burner Tripod Beaker: glass or plastic; common sizes are SO—mL, 100—mL, 250-mL, 400-mL; glass beakers may be heated. Buret: glass; common sizes are 25-mL, and 50—mL; used to measure volumes of solutions in titrations. Ceramic square: used under hot apparatus or glassware. Clamps; the following types of clamps may be fastened to support apparatus: buret/test-tube clamp, clamp holder, double buret clamp, ring clamp, 3-pronged jaw clamp. Clay triangle: wire frame with porcelain supports, used to support a crucible. Condenser: glass; used in distillation procedures. Crucible and cover: porcelain, used to heat small amounts of solid substances at high temperatures. Crucible tongs: iron or nickel, used to pick up and hold small items. Dropper pipet: glass tip with rubber bulb, used to transfer small volumes of liquid. Erlenmeyer flask: glass, common sizes are lOO-mL, 250-mL', may be heated, used in titrations. 10 Laboratory Equipment Evaporating dish: porcelain, used to contain small volumes of liquid being evaporated. Florence flask: glass, common sizes are 125-mL, 250-mL, 500-mL, may be heated, used in making and for storing solutions. Forceps: metal, used to hold or pick up small objects. Funnel: glass or plastic, common size holds 12.5-cm diameter filter paper. Gas burner: constructed of metal; connected to a gas supply with rubber tubing; used to heat chemicals (dry or in solution) in beakers, test tubes, and crucibles. Gas collecting tube: glass, marked in mL intervals; used to measure gas volumes. Glass rod with nichrome wire: used in flame tests. Graduated cylinder: glass or plastic, common sizes are lO—mL, 50-mL, 100—mL, used to measure approximate volumes; must not be heated. Graduated pipet: glass, common sizes are 10—mL, 25-mL; used to measure solution volumes; less accurate than a volumetric pipet. a... «.4. _ 3-prong jaw clamp Forceps Stirring Condenser POliceman Volumetric pipet Graduated cylinder Thermometer Gas collecting tube Pipet bulb Graduated pipet Buret .m, ,, > Double buret clamp Hing clamp Platform balance (triple beam) Mortar and pestle: porcelain, may be used to grind crystals and lumpy chemicals to a powder. Pipet bulb: rubber, used in filling a pipet with a solution, a pipet must never be filled by mouth. Plastic wash bottle: flexible plastic, squeeze sides to dispense water. Platform balance: also known as a triple beam balance. Pneumatic trough: galvanized container with shelf, used in experi- ments where a gas is collected. Ringstand: metal rod fixed upright in a heavy metal base; has many uses as a support. Rubber stoppers: several sizes. Rubber tubing: used to connect apparatus so as to transfer liquids or gases. Safety goggles: plastic; must be worn at all times while working in the laboratory. Screw clamp, pinch clamp: metal, used to block off rubber tubbing. Spatula, scoopula: metal or porcelain; used to transfer solid chemicals; the scoopula has a larger capacity. Stirring rod and rubber policeman: glass with rubber sleeve; used to stir, assist in pouring liquids, and for removing precipitates from a container. Test tube brush: bristles with wire handle, used to scrub small diameter glassware. Test tube holder: spring metal, used to hold test tubes or glass tubing. Test tube rack: wood or plastic, holds test tubes in a vertical position. Test tubes: glass, common sizes small (13 mm x 100 mm), medium (20 mm x 150 mm), large (25 mm x 200 mm), may be heated. Thermometer: mercury in glass, common range - 10°C to 110°C. Triangular file: metal, used to scratch glass tubing prior to breaking to desired length. Tripod: iron, used to support containers of chemicals above the flame of a burner. Volumetric pipet: glass, common sizes are 10-mL, 25-mL, used to measure solution volumes accurately, must not be heated. Watch glass: glass, used to cover an evaporating dish or beaker. Wide-mouth bottle: glass, used with pneumatic trough. Wire gauze: used to spread the heat of a burner flame. Laboratory Equipment 11 v, . t l . l ,l i ‘ l Figure 4. Pouring from a reagent bottle into a beaker. Q A Figure 2. Folding the filter paper. Guide flow of liquid with a glass rod Solid collects Q). on filter paper Stem touches side of J Filtrate being Figure 3. Filtration assembly. 1 2 Safe Laboratory Techniques Sate Laboratory Techniques W Pouring Liquids 0 Always read the label on a reagent bottle before using its contents. - Always wear safety goggles when handling chemicals. - Never touch chemicals with your hands. ° Never return unused chemicals to their original containers. To avoid waste, do not take excessive amounts of reagents. Follow this procedure when pouring liquids. 1. Use the back of your fingers to remove the stopper from a reagent bottle. Hold the stopper between your fingers until the transfer of liquid is complete. Do not place the stopper on your workbench. 2. Grasp the container from which you are pouring with the palm of your hand covering the label. 3a. When you are transferring a liquid to a test tube or measuring cylinder, the container should be held at eye level. Pour the liquid slowly until the correct volume has been transferred. 3b. When you are pouring a liquid from a reagent bottle into a beaker, the reagent should be poured slowly down a glass stirring rod (Figure 1). When you are transferring a liquid from one beaker to another, you can hold the stirring rod and beaker in one hand. Filtering 0 Mixture Sometimes it is necessary to separate a solid (for example, a precipitate) from a liquid. The most common method of separating such a mixture is filtration. 1. Fold a filter paper circle in half and then quarters. Open the folded paper to form a cone with one thickness of paper on one side and three thicknesses on the other (Figure 2). 2. Put the paper cone in a filter funnel. Place the funnel in an iron ring clamped to a ring stand. Moisten the filter paper with a small volume of distilled water, and gently press the paper against the sides of the funnel to give a good fit. (If the correct size of filter paper has been used, the top edge of the cone will be just below the rim of the filter funnel.) 3. Place a beaker beneath the funnel to collect the filtrate. The tip of the funnel should touch the inside surface of the beaker and extend about one inch below the rim (Figure 3). 4. Decant the liquid from the solid (precipitate) by pouring it down a glass stirring rod into the funnel. Be careful to keep the liquid below the top edge of the cone of filter paper at all times; the liquid must not overflow. Finally, use a jet of distilled water from a wash bottle to wash the solid (precipitate) into the filter. 5. When the filtration is complete, wash the solid residue on the filter paper with distilled water to remove traces of solvent. Dry the solid. 6. If the filtrate contains a dissolved salt it may be recovered by evap- oration if desired. .' l g i ll . Figure 4. Laboratory gas burners. Smoky yellow flame Luminous flame (yellow) 2. air vents closed ,I r l ’ ._ Outer cone Hottest part of flame Inner cone Non-luminous flame (light blue) b. air vents open Figure 5. Burner flame characteristics. <——— Burner tube Air vent (adjust by rotating sleeve) Bunsen burner Air vents (adjust by screwing burner tube up or down) Gas inlet / (main gas "‘ valve should Gas inlet (regulate be fully gas flow with the open) main gas valve) I " Gas control valve (regulate gas flow with this valve) Tirrell burner Using a Gas Burner Laboratory gas bumers produce various kinds of flames when different mixtures of gas and air are burned. The two most common models are the Bunsen burner and the Tirrell burner. Both have adjustable air vents; the Tirrell burner also has a gas control valve in its base (Figure 4). 1 . Examine your laboratory burner. Determine which model you have. 2. Connect the burner to the gas supply with rubber tubing. 3. Close the air vents. If your model is a Tirrell burner also close the gas control valve at the base of the burner. 4. Hold a lighted match at the top of the burner tube and turn on the gas supply. Do this by opening the main gas supply valve located on top of the nozzle to which you attached the rubber tubing. (If your model is a Tirrell burner, open the gas control valve at the base approximately 1/2-turn after opening the main gas supply valve.) You should get a yellow or luminous flame (Figure 5). When a Tirrell burner is used, the main gas supply valve should be opened fully and the gas flow regulated by the gas control valve. Gas supply to a Bunsen burner is controlled by the main gas valve. 5. Open the air vents slowly, to admit more air into the flame, to produce a light blue (nonluminous) cone—shaped flame. If the flame “blows out” after lighting, the gas supply should be reduced. 6. Adjust the air vents and gas supply to produce the desired size of flame. For most laboratory work the bl...
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