Common Laboratory Procedures

COMMON LABORATORY PROCEDURES D) Common Laboratory Procedures D-1. Handling Solids General Guidelines for Handling Solids  Use a clean spatula or scoopula to transfer solid from bottles. Never use a contaminated spatula.  Never return unused solid to the reagent bottle. To eliminate waste, avoid removing more solid from a bottle than is necessary.  Never discard chemicals in the trashcan. Follow waste disposal procedures outlined in the Laboratory Manual. Quantitative Transfer Quantitative transfer refers to moving of all the contents to be transferred from one container to another. Below is an illustration of how to properly weigh and transfer a solid using weighing paper. You will be using weigh boats rather than weighing paper, but the procedure is essentially the same. Figure 1 Quantitative Transfer of Solids A-13 COMMON LABORATORY PROCEDURES Using the Desiccator You will occasionally be asked to use the desiccator during the laboratory course to dry some reagents. The desiccator contains some amount of desiccant, which absorbs moisture from air.  Keep the desiccator closed at all times. The desiccant will absorb moisture in the air extremely rapidly.  Keep the desiccator tightly sealed with some vacuum grease. To apply vacuum grease, put a pea-sized amount of grease on a paper towel and wipe it along the rim of the transparent cover. Make sure you do not use too much grease. Place the cover on top of the base and twist the cover 30 degrees to ensure a tight seal.  Desiccator Care In the Chemistry 2 lab, we use Calcium Chloride as the desiccant. If water is found in the desiccator, discard the desiccant in the sink and rinse with copious amount of water until all solids are dissolved. Wipe the desiccator dry with a paper towel. Make sure all traces of water are removed before refilling from the 10 kg bucket of Calcium Chloride in your lab.  Hard to Open Desiccator Do not try to force open a desiccator. You may accidentally shatter the glassware stored inside. Use an aluminum scoopula as a wedge and push it slowly into the space between the covers. Notice Always keep the desiccator upright and closed in your locker. Clean up Calcium Chloride spill immediately. Moisture will damage drawers. A-14 COMMON LABORATORY PROCEDURES D-2. Handling Liquids Drawing Solutions from a Reagent Bottle Most reagent bottles in your laboratory have a small test tube holder for a disposable (dispo) plastic pipette. To avoid cross-contamination, always use the assigned dispo pipette to draw solutions from the reagent bottle. Do not use your glass pipette with reagent bottles. Caution Improper use of disposable pipets may cause serious injuries! Never point the pipet at yourself or others! Do not squeeze air into solutions with the dispo pipet. May result in chemical splashes. Always put full dispo pipet in a test tube when carrying it to another part of the lab. Estimating Volume with a Dispo Pipet The dispo pipette may be used to transfer an estimated amount of solution. This is useful when working with non-limiting reagents or quickly making a solution that will be titrated later. To draw 1mL of solution into an empty dispo pipet: 1. Squeeze the bulb to remove some air from the dispo pipet. 2. Submerge the tip of the dispo pipet in the solution. 3. Slowly release the pressure on the bulb and draw solution to the 1mL mark. 4. Without releasing pressure on the bulb, steadily remove the dispo pipet from the solution. 0.25 mL Transferring Liquid  When transferring liquids from a reagent bottle, 1mL always remove the cap/stopper and hold it in your hand. Never place the cap/stopper on the bench or contamination could result. A-15 COMMON LABORATORY PROCEDURES Pour the liquid slowly and carefully to avoid spillage. You may find the use of a glass rod helpful, as shown below. Figure 2. Liquid Transfer with Glass Stir Rod  With the exception of beakers, you should always use a funnel when transferring liquids from a container with a large opening to a container with a small opening. D-3. Capping a Flask with Parafilm During many experiments you will have to cap a flask to protect the contents from contamination. Figure 4 illustrates the proper method using Parafilm. Figure 3 Capping A Flask Measuring Liquid Volumes Many glassware items have volume marks printed on them. Before using a piece of glassware to make a volume measurement, you should take a moment to study its calibrations to insure that you know how to read them properly. A-16 COMMON LABORATORY PROCEDURES  A beaker or Erlenmeyer flask can be used for rather rough measurements.  A graduated cylinder can be used for measurements of moderate accuracy.  A pipet is commonly used to transfer an accurately known volume of a liquid. However, the accuracy of such a transfer is only as good as the technique of the operator will allow. In making any volume measurement, the liquid level should always be the same as your eye level. Erlenmeyer flasks and graduated cylinders are usually filled/read by raising them to your eye level rather than by squatting down to bring your eye level to the bench top. The liquid level in a pipet is always lowered to the mark while the mark is held steady at eye level. Burets: With practice, the position of the meniscus of a liquid in the 25 mL burets used in the Chemistry 2 labs can be estimated to within 0.02 mL. Error! Reference source not found. shows the use of a card with a dark strip on it to sharpen the image of Figure 4 Reading the Meniscus the meniscus. You will find by experiment that if the top of the strip is positioned slightly below the level of the liquid in the buret, the bottom of the meniscus will be very easy to see. D-4. Common Glassware in the Laboratory Almost all of the glassware used in the Chemistry 2 laboratories are made with borosilicate glass, which is able to resist high temperatures and most chemicals. Care and Maintenance of Laboratory Glassware  Always examine the glassware for chips and scratches before use. Damage glassware may break during normal usage or cause bodily injuries.  Never place glassware near the edge of lab bench. Keep the work area clean and organized to prevent accidents and chemical spills.  Clean broken glassware must be disposed of inside the designated Glass Disposal Box. If box is full, ask the dispensary for a new one.  Clean all glassware with water. Make sure to rinse the glassware with DI water as a final step.  Never heat glassware to dryness. Add cold water with your 250 mL water squeeze bottle when needed.  Never place a heated beaker in an ice bath, or vice versa. Allow the glassware to warm up or cool down gradually. A-17 COMMON LABORATORY PROCEDURES  Never carry lab ware by the neck or cap. Always hold lab ware from the bottom and the side.  Never use tape or sticky labels on laboratory glassware. Always write on the white or blue label area with graphite pencil (a.k.a. “lead pencil”). Beakers Beakers can be used in the laboratory to estimate volume, storing liquids temporarily, and carry out certain reactions. pouring lip volume mark  Always hold beakers from the bottom or the side. Never hold a beaker by the rim.  All beakers in the Chemistry 2 laboratories have a pouring lip to make pouring solutions easier.  All beakers in the Chemistry 2 laboratories have marks for estimating the volume. As noted on the glassware, there is a ±5% error for the largest volume mark.  Place a 100 mm watch glass on top of beaker when boiling water to speed up the process.  If needed, write labels in the frosted areas on the beaker with graphite pencils (a.k.a. “lead” pencils). Do not use wax pencil or pen! Erlenmeyer Flasks  All Erlenmeyer flasks in the Chemistry 2 laboratories have marks for estimating the volume. As noted on the glassware, there is a ±5% error for the largest volume mark.  If needed, write labels in the frosted areas on the beaker with graphite pencils (a.k.a. “lead” pencils). Do not use wax pencil or pen! A-18 volume marks Erlenmeyer flasks can be used in the laboratory to estimate volume, storing liquids temporarily, and carry out certain reactions. COMMON LABORATORY PROCEDURES Graduated Cylinder Graduated cylinders are used to measure a small volume of liquid with more precision than beakers and Erlenmeyer flasks.   The graduated cylinders in the Chemistry 2 laboratories include a plastic base and a plastic ring. The plastic ring is to protect the glass cylinder when the glassware is knocked over. Make sure the plastic ring is place near the top of the cylinder. plastic ring keep above 0mL mark graduation marks plastic base To quickly measure out a specific amount of water, fill your 250 mL water squeeze bottle with DI water and squeeze the desired amount of water into the graduated cylinder. Volumetric flasks are very precisely calibrated glassware designed to contain one specific volume of liquid. You will only be allowed to have a limited number of volumetric flasks. If you need to make multiple solutions accurately with a volumetric flask, do not use multiple volumetric flasks. Instead, pour solutions you made in another container and reuse the same volumetric flask. 10mL 250mL mark Volumetric Flasks 240mL  The 250 mL volumetric flask used in the Chemistry 2 laboratories has only one graduation mark for volume of 250 mL. As noted on the glassware, there is a ±0.12 mL error at 20 °C.  To fill a volumetric flask to the mark, quickly fill the flask to the neck. Cap the bottle and swirl or invert if needed. Then use a 250 mL water squeeze bottle to fill to the volume mark. Notice that the volume between the neck and the 250 mL volume mark is only 10 mL.  Never use glass pipets or dispo pipets with the volumetric flasks. Pipets will become stuck inside the flasks. Burets Burets are used to deliver a precise amount of solution. Unlike the volumetric flask and graduated cylinder, which are calibrated to measure the liquid contained in the glassware, A-19 COMMON LABORATORY PROCEDURES burets are calibrated to measure the liquid delivered from the glassware. In the Chemistry 2 labs, the buret is mostly used for titrations. Filling the buret with DI water 1. Always remove the buret and hold it below your eye level when filling the buret. 3. Always use a small beaker (100 mL or 150 mL). For a 25 mL buret, pour 30-40 mL of DI water into the beaker. 4. Hold the buret slightly below the 0mL mark with one hand; slowly pour into the buret the solution from the beaker in your other hand. Stop before the liquid level reaches 0 mL. 25mL volume 2. Check to make sure the stopcock is in the closed position. 0mL mark graduation marks stopcock closed when horizontal Cleaning the buret 1. To clean a buret, fill it to half way with DI water. 2. At the sink, open the stopcock and drain out ~10 mL of water and close it. Then invert the buret and open the stopcock and drain out the rest from the top. Conditioning the buret You should always condition your buret with your working solution before using it. 1. Clean the buret with DI water. 2. Fill the buret with 8-10 mL of the solution to be used. Open the stopcock to drain out a small amount from the tip into an appropriate waste container. 3. Cap the top end with Parafilm. At the sink, hold the top of the buret between the thumb and finger of one hand, and hold the tip of the buret with another. Turn the buret horizontal and rotate the tip of the buret. Make sure all sides of the buret are washed with the solution. 4. Pour the remaining solution in the buret into an appropriate waste container. A-20 COMMON LABORATORY PROCEDURES Dispensing solution from the buret 1. First, fill the buret with your solution to near the 0mL mark, but do not attempt to fill it to exactly 0.00 mL. Open the stopcock and drain out a very small amount to ensure no air bubbles exist in the tip. Record in your lab notebook your buret initial reading. 2. Open the stopcock and drain the solution. Stop when the target volume is reached. Record the buret final reading in your lab notebook. The difference between the initial reading and final reading is the volume dispensed. 3. To dispense in small quantities, quickly turn the stopcock clockwise exactly 180 degrees. Repeat as needed. Volumetric Pipet Similar to the buret, the volumetric pipet is designed to deliver a precise amount of solution.  The volume of liquid each pipet is designed to deliver is labeled on the glassware. Use the volumetric pipet only when you need to deliver the exact amount of solution with precision.  There is a bottle of volumetric pipet cleaning solution in each laboratory. Draw the cleaning solution into the pipet with a pipet bulb and dispel the solution  To condition a volumetric pipet, draw a small amount of your working solution into the pipet just above the volume mark. Drain the solution into an appropriate waste container.  Follow the illustration below to learn how to use the volumetric pipet. You should practice using deionized water first to become proficient with the techniques. Caution  Never mouth pipet. Always use the pipet bulb with tip attached.  Never point your pipet or pipet bulb at yourself or others.  Never squeeze air into solutions as it may cause chemical splash.  Never draw solutions into the bulb. Corrosive solutions will dissolve the rubber and contaminate the pipet. A-21 COMMON LABORATORY PROCEDURES 1. To begin:  With your dominant hand, hold the conditioned pipet vertical and the pointed end downward inside the container of your working solution. Place your hand near the top of the pipet and keep your index finger free so that it can easily cap the pipet.  With your other hand, deflate the rubber pipet bulb with tip with your thumb.  Place the tip inside the top of the pipet. 2. To draw the solution:  Slowly release your thumb and draw the liquid up the pipet and a few centimeters above the mark on the pipet. Keep the pipet submerged in solution to avoid drawing up air.  Lower the pipet so that it reaches the bottom of the container. Quickly remove the pipet bulb with tip and cap the pipet with your index finger. 3. To adjust the volume:  Raise the over-filled pipet. Raise the mark on the pipet to your eye level, tilt the receiver slightly, and touch the pointed tip of the pipet to a dry spot on its sidewall.  Rotate the pipet left and right slightly and let a small amount of air to enter the pipet and thereby allow the meniscus to fall exactly on the volume mark. Be patient because if you overshoot the mark you must begin the whole process again. A-22 COMMON LABORATORY PROCEDURES 4. To deliver the liquid:  Remove the accurately filled pipet from its container. Quickly dry the lower portion of the shaft with a single downward stroke of a laboratory tissue.  Tilt the final receiver slightly and while holding the pipet vertical, place its tip against the receiver wall so that when take your finger off of the pipet mouth, liquid will flow smoothly down to the bottom of the vessel. Avoid splashing.  Do not squeeze solution out with the pipet bulb with tip and do not blow out the last drop. The pipet is calibrated to deliver with one last drop left in the pipet. A-23 COMMON LABORATORY PROCEDURES D-5. Using the Balance A balance is used to measure the mass of an object. There are 4 analytic balances assigned to your laboratory section for use in the adjoining balance room. These balances measure the mass to the nearest milligram. You will use these balances for most mass measurements in the Chemistry 2 lab experiments. There is also a less precise “quick” balance in your lab room, between the fume hoods. You may use this balance to make rough measurements of non-limiting reagents quickly and speed up your experiment without compromising the experiment results. On/Off Switching  To turn on the balance, remove all load from the weighing pan and press the On button.  To turn off the balance, press and hold the Off key for 2 seconds. Simple Weighing Open one of the draft shield sliding door. Make sure the balance pan and surrounding area is clean. You can clean it with a balance brush or Kimwipe. Next shut the doors and press the 0/T to set the balance at zero. Now simply place the object to be weighed on the weighing pan and measure the mass to 0.001 grams. Draft Shield Weighing Pan LCD Display Keys Figure 5. The Analytical Balance Notice Always use weighing boats when weighing solids to protect the balance. To do this simply place the plastic weighing boat on the balance pan and be sure it is not touching the side. Always use the balance with extreme care, as it is very expensive. A-24 COMMON LABORATORY PROCEDURES Taring To measure the mass of sample inside a container, perform the following procedures: 1. Place the empty container (e.g. a weighing boat) on the balance. 2. Press the 0/T key briefly. The display should read 0.000 g. 3. Add the sample to the container. Read the displayed mass to 0.0001 g. Weighing by Difference To measure the mass of a sample by difference 1. Clear the weighing pan. Press 0/T. The reading should be 0.000 g. 2. Place the container with the sample on the balance. Record the mass. 3. Remove a portion of the sample from the container. 4. The difference between the two readings is the Figure 6 Taring mass of the removed portion of the sample. D-6. Using the Centrifuge A centrifuge machine is used to separate the different constituents of a solution by their density. In many experiments, you will be required to separate precipitation products from solution using the centrifuge machine. Centrifuge Cover Rotor with Aluminum Shields Cover Latches (one on each side) On/Off Switch Figure 7 The Centrifuge A-25 COMMON LABORATORY PROCEDURES Procedure 1. Always load centrifuge tubes of about equal weight. Fill another centrifuge tube with water to equal weight to balance. 2. To balance the tubes, place a small beaker on the “quick” balance in your lab room. Weigh your sample tube. Fill another centrifuge tube with water to equal weight (to the nearest 1g). 3. Place the centrifuge tubes in the aluminum shields on opposite sides. The centrifuge tubes should fit inside the aluminum shield snugly. Use a different tube if more than 1/8 inch of the glass is exposed. 4. Close the cover. Lock both sides securely into the latches. 5. Press the On/Off switch to turn on the unit. Press the switch again to turn it off. Warning Improper use of the centrifuge machine may result in serious injury. Follow all safety precautions when operating the centrifuge machine. Safety Precautions  Operate the centrifuge only when the cover is securely closed.  Never open the cover when the centrifuge is running.  Always balance the tubes before loading. Only spin 2, 4, or 6 tubes.  Never spin 1, 3, or 5 tubes.  Turn off the machine immediately if there are signs that the load is unbalanced.  Never open the cover before the rotor comes to a complete stop.  Never stop the rotor with your hand. Serious injury may result. D-7. Using the Hot Plate The hot plate is used to heat solutions in nearly all experiments performed in the Chemistry 2 laboratory. However, improper use of the hot plate may result in serious injury. Follow all instructions and exercise caution when using the hot plate. A-26 COMMON LABORATORY PROCEDURES There are a variety of hot plates used in the Chemistry 2 labs, but they all have the same essential features. Ceramic Top Indicating Lights Heating Control Knob Stirring Control Knob Figure 8 The Hotplate/Stirrer Features  The Ceramic Top: The heating surface. The temperature may reach a maximum of over 400 °C. Do not touch the ceramic top. It may cause serious burns. The ceramic top is also very delicate. Clean up spills immediately and avoid hitting the surface with heavy objects.  There are four common indicating lights on all models used in the Chemistry 2 laboratories. They are: the Power Indicator, the Heat Indicator, the Stir Indicator, and the Hot Top indicator. o Power Indicator: On if the unit is plugged in to a power source. Check power cord connection if not on. o Heat Indicator: On if the heat is turned on. o Stir Indicator: On if the magnetic stirrer is turned on. o Hot Top Indicator: On if the top has a temperature of over 60°C. Do not unplug the unit if the top plate is still hot. Warning The hot plate may cause series burns. Avoid touching the top plate and follow all safety precautions. A-27 COMMON LABORATORY PROCEDURES Safety Precautions  Keep the power cord away from the heating surface. The cord may melt and cause an electrical hazard.  Do not hit the top with heavy objects. It may break if impacted.  Do not heat volatile or flammable materials.  Do not operate near volatile or flammable materials. The hot plate must not be used during these experiments:   2A. Determination of Avogadro’s Number  2B. Colligative Properties Avoid spilling liquids on the ceramic top. Do not over boil solutions. It takes approximately 15 minutes to boil 400 mL of water at Heat setting 6. Avoid turning the heat setting too high. Spills from over-boiling will damage the hot plate and may result in personal injury.  Never use a container larger than the top plate.  Never boil a solution to dryness. A-28 COMMON LABORATORY PROCEDURES D-8. Heating with a Bunsen Burner In using a Bunsen burner, always use a tight blue flame as shown in the illustration below. Always estimate the appropriate height for the iron support ring before turning on the Bunsen burner. Control the heat transfer by adjusting the distance from the burner to the object. Note that the distances suggested in the manual are measured from the hottest part of the flame to the object. Figure 9 The Bunsen Burner Warning Only use the Bunsen burner when specifically instructed by the lab manual. Keep all flammable materials away from the Bunsen burner. Heated lab ware including iron rings can be extremely hot and may cause serious burns! A-29 COMMON LABORATORY PROCEDURES D-9. Filtration You will often need to separate a liquid from a solid. At times you will simply decant, that is, you will carefully pour out the liquid, leaving the solid behind. At other times you will need to filter the solution. To do this you will use filter paper and a funnel. You must first fold the paper in order to accelerate the process; this is shown in Figure 7. You will then set the paper in the funnel using your wash bottle. To do this simply place the paper Figure 10 Fluting the Filter Paper into the funnel and add a small amount of water to the bottom of the filter. Slowly add water to the sides with a circular motion to avoid air bubbles between the paper and the funnel. Once the paper has set, transfer the solution to be filtered. If the solid has settled, decant the liquid through the filter first in order to save time. Never overwhelm the filter; don't add the solution too quickly and never come to within one centimeter of the top of the paper. Transfer the solid using a wash bottle and rubber policeman, and then wash the solid as directed by the experimental procedure. A-30 COMMON LABORATORY PROCEDURES D-10. pH Meter Operating Instructions A. Preparing the pH meter A-1. Turn on the pH meter A-2. Meter must be in pH mode. If in mV mode, press pH/mV button. ̅. If not shown, A-3. Make sure pH meter is showing /A press and hold Read button for 2 seconds. A-4. Lower left window must show B1 7.00 4.00 10.00 1.68. If not, ask your TA to adjust the setting. A-5. You may adjust the electrode stand to secure the electrode. Loosen the tension knob to adjust arm position and tighten the tension knob before use. Caution Do NOT place test tubes on electrode stand! A-31 COMMON LABORATORY PROCEDURES A-6. Do NOT let electrode dry out. Always store electrode in sat. KCl solution when not in use. B. Calibrating the pH meter Note: You only need to calibrate the pH meter once per lab period. B-1. Rinse the electrode with DI water. B-2. Blot dry with Kimwipe. WARNING: Do NOT rub the electrode with Kimwipe. Rubbing the electrode may build up static charge and damage the electrode. B-3. Place electrode in pH 7 buffer standard (yellow). B-4. Press the Cal button. B-5. Wait for the display to stop blinking. A-32 COMMON LABORATORY PROCEDURES B-6. Repeat step B-1 to B-5 with the pH 4 buffer standard (red) and with the pH 10 buffer standard (blue). C. Measure the pH of sample C-1. After calibration, place electrode in sample solution and press Read. C-2. Wait for the reading to stabilize. A-33 COMMON LABORATORY PROCEDURES D-11. Fume Hood Use and Safety The fume hoods in the laboratory protect personnel from hazardous materials and inhalation of toxic materials. Features of the Fume Hood Flow Monitor with Emergency button and Mute button Light Switch Certification Sticker Sash Sash Stop Work Surface Airfoil Before Using the Fume Hood  Check the certification sticker (). The Fume Hood is tested and certified every year.  Check the flow monitor (). Laboratory fume hood should have 100 ft/min face velocity or more. Lower the sash if to increase airflow. If airflow does not reach 100 ft/min, stop work in the fume hood and contact safety personnel immediately.  Turn on light switch (). Working With the Fume Hood  Lift the sash up slowly about 12 inches. Never raise the sash above the sash stop().  Always place lab equipment at least six inches away from the edge and inside the fume hood as much as possible.  Do not rest body parts on the edge or the Airfoil ().  Do not place glassware or chemicals on the Airfoil ().  Move unused equipment and chemicals away. Remove your glassware when done. Remember, you are sharing the fume hood with 23 other students. Remove your glassware as soon as possible and clean your glassware. Do NOT abandon your lab ware in the fume hood!  When increased airflow is needed, press the Emergency button and the Mute button.  Clean up spills immediately.  Cap all containers immediately. A-34 COMMON LABORATORY PROCEDURES  Turn off Emergency mode, close hood sash all the way at the end of lab. Fume Hood Usage in Chemistry 2 Laboratory  Always use the fume hood when directed by the Laboratory Manual. Certain reactions in the Chemistry 2 curriculum generate toxic or flammable gases. Follow instructions to protect yourself and others in the lab.  Many hazardous chemicals are kept in the fume hood. Never remove these containers unless specifically directed by the Laboratory Manual.  All Hazardous Waste containers for the Chemistry 2 course are kept in the fume hood. Fume Hood Emissions A. Minimize fume hood emissions to protect the environment and air quality. B. Never evaporate waste in the fume hood. C. Minimize use of volatile liquids. Close and seal after using. If you have questions, contact your TA or safety coordinator. A-35