Basic Tools and Operations in Anal Chem PDF

Basic Tools and Operations of Analytical Chemistry Tools in Heating, Evaporating, Solvent Removal and Refluxing Liquids Open-Dish Evaporation Evaporating dish Florence Flasks Evaporating dish 3. hot plate Used for heating substanc...

Basic Tools and Operations of Analytical Chemistry Tools in Heating, Evaporating, Solvent Removal and Refluxing Liquids Open-Dish Evaporation Evaporating dish Florence Flasks Evaporating dish 3. hot plate Used for heating substances and Florence Flasks liquids in beakers and flasks.  Water baths heated on a hotplate, are most commonly used to heat solutions to 100o C-100oC (boiling baths). Boiling water bath Water bath to cool an apparatus Heating a flask with a Allowing a flask to cool. sand bath. Oil baths are much like water baths, but use silicone or mineral oils in order to enable temperatures hotter than the boiling point of water (> 100oC100oC) It is also quite common for the oil to be electrically heated, through immersion of a coiled wire connected to a "Variac" (light blue piece of equipment) wire gauze Used with a ring clamp to support glassware over a Bunsen burner. Spreads flame out for more even heating. striker Used to light a gas burner. crucible tong Used to hold crucibles and evaporating dishes when they are hot. Reflux apparatus Reflux apparatus, with arrows indicating the direction of water flow, b) Reflux diagram c) Incorrect clamping of a reflux apparatus. A reflux setup allows for liquid to boil and condense, with the condensed liquid returning to the original flask. A reflux setup is analogous to a distillation, with the main difference being the vertical placement of the condenser. The liquid remains at the boiling point of the solvent (or solution) during active reflux. Step-by-Step Procedures a) Pouring in solution, b) Reaction using a stir bar (solution is colorless), c+d) Same reaction using boiling stones. Using a sandbath a. Filling a heating mantle with sand to ensure a perfect fit b. Heating a reflux apparatus with a sand bath. c. Do not turn off the water flowing through the condenser until the solution is only warm to the touch. After a few minutes of air cooling, the round bottomed flask can be immersed in a tap water bath to accelerate the cooling process Reduced-Pressure Evaporation Evaporation can be accomplished from a solution quickly by placing it in a side-arm flask, sealing the flask, and then applying vacuum. Rotary Evaporator remove liquids from preparations that need to be dry. prepare samples for analysis.  Rotary Evaporators A piece of apparatus consisting of a motor unit that rotates the evaporation flask, a vacuum system, a heated water bath and a condenser, which is used to remove solvents from samples under reduced pressure. Distillation Simple distillation can be used to remove solvent. It works well if the solution is composed of a solid and a low- boiling solvent, or if the solution is composed of a high- boiling liquid and a low-boiling solvent (BP differences >100°). Steam Distillation Steam distillation is used to distil compounds at a temperature lower than the normal boiling point. The desired material distilled at a temperature of fewer than 100 OC Major conditions are observed to use steam distillation: 1.Extraction of temperature sensitive compounds 2.When material to be extracted is immiscible 3.When substance is chemically non reactive with water.  Fractional Distillation process by which components in a chemical mixture are separated into different parts (called fractions) according to their different boiling points.  Use for filtering non-gelatinous precipitates. Fig. 2.21. Filtering crucibles: (a) Gooch crucible; (b) sintered-glass crucible; (c) porcelain filter crucible. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Beaker Used to hold, mix, and heat liquids. Test Tube Used to hold and mix liquids. Test Tube Clamp Used to hold a test tube, particularly when hot. Test Tube Rack Used to hold several test tubes at one time.  Used to dry samples before weighing. Usually 110o C used. Fig. 2.18. Drying oven. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Measuring Mass  Types of Analytical Balances An analytical balance is a weighing instrument with a maximum capacity that ranges from 1 g to a few kg with a precision of at least 1 part in 105 at maximum capacity. Macrobalances have a maximum capacity ranging between 160 - 200 g; measurement can be made with a standard deviation of ±0.1mg.  Types of Analytical Balances Semimicroanalytical balances have a maximum load of 10 - 30 g with a precision of ±0.01mg. Microanalytical balance has a capacity of 1 -3 g and a precision of ±0.001mg. Modern balances are electronic. They still compare one mass against another since they are calibrated with a known mass. Common balances are sensitive to 0.1 mg. ©Gary Christian, Analytical Chemistry, Fig. 2.1. Electronic analytical balance. 6th Ed. (Wiley)  Electronic balances operate on the principle of emf compensation – the compensation current to bring the pan back to its position original position is proportional to the sample scanner weight. hanger coil temperature sensor ©Gary Christian, Analytical Chemistry, Fig. 2.2. Operating principle of electronic balance. 6th Ed. (Wiley)  Mechanical balances operate as first class levers. M1L1 = M2L2 ©Gary Christian, Fig. 2.3. Principle of analytical balance. Analytical Chemistry, 6th Ed. (Wiley) The single pan balance operates by removing weights equal to the mass of the sample. Small residual imbalances are read optically from the deflection of the beam. Fig. 2.4. Schematic diagram of a typical single-pan balance. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) The single-pan balance is as accurate as electronic balances, and almost as fast. But it can’t be interfaced to a computer to collect and process data. And you have to read a scale instead of a digital number. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Fig. 2.5. Typical single-pan balance. Weighing bottles are used for drying samples. Hygroscopic samples are weighed by difference, keeping the bottle capped except when removing the sample. Fig. 2.6. Weighing bottles. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) A weighing dish or boat is used for direct weighing of samples. Fig. 2.7. Weighing dish. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  Desiccators and Desiccants Oven drying is the most common way of removing moisture from solids. This approach is not appropriate for substances that decompose or for those from which water is not removed at the temperature of the oven.  Desiccators and Desiccants Dried material are stored in desiccator while they cool so as to minimize the uptake of moisture. The base section of the desiccator contains a chemical drying agent (desiccants) such as anhydrous calcium chloride, calcium sulfate, magnesium perchlorate or phosphorus pentoxide. Desiccator  CaCl2 is commonly used. It needs periodic replacement when wet or caked. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Factors that affect readings on analytical balances: Temperature Vibrations Air drafts Chemical reactions Uncalibrated scales Magnets User error Improper grounding Slope Inappropriate handling of the sample Five precautions for accurate sample weighing: 1. Keep the balance calibrated The scales’ calibration must be validated as per the requirements of a recognized national calibration laboratory. Keep the balance calibrated using the standard calibration procedures against daily, weekly, and monthly schedules. Never touch the standard weights with your hands. Five precautions for accurate sample weighing: 2. Ensure appropriate environment Check the horizontal positioning of the balance. Keep the balance in a vibration-free environment. Ensure that you place the balances in an area with controlled humidity and temperature. They should not be exposed to direct Thermohygrometer sunlight since it can cause temperature variations inside the weighing chamber. Five precautions for accurate sample weighing: 2. Ensure appropriate environment Don’t place the balances next to doors or windows since opening or closing them will result in air drafts. This could affect the weighing process. Ensure that you weigh the samples only after closing the weighing chamber doors. Keep the weighing chamber clean to prevent cross-contamination of samples and erroneous readings. Five precautions for accurate sample weighing: 3. Handle the weights properly Never touch the weights with bare hands. Hand grease can cause errors in the readings. Use a pair of clean forceps while placing the samples. Use wooden tweezers or tweezers covered with rubber on the tips to prevent the weights from getting scratched. Use gloves when handling heavy weights. 4. Store the weights in the right manner Always store the weights in a room free of moisture, corrosive gases, and dust. If the weights get rusted or dust sticks to them, the mass of the weights will increase. This will result in inaccurate readings. After using the weights, place them inside a desiccator to keep them dry  5. Take the right measures to weigh the samples Use a clean spatula of appropriate size while placing the sample. Weigh the sample quantity in a a flask rather than opting for butter paper weighing. The latter can introduce errors. Before you record the readings, allow them to stabilize. Correcting Mass for the Buoyancy of Air Because of the buoyancy of air, an object always weighs less in air than it does in a vacuum. Correction for buoyancy Wv- object’s true weight in vacuo Wa- weight in air Do - object’s density Dw -density of the calibration weight, and 0.0012 - density of air under normal laboratory conditions (densities in units of g/cm3). The greater the difference between Do and Dw the more serious the error in the object’s measured weight. Example: A 10-mL volumetric pipet was calibrated using a balance calibrated with brass weights having a density of 8.40 g/cm3. At 25 oC the pipet dispensed 9.9736 g of water. What is the actual volume dispensed by the pipet and what is the determinate error in this volume if we ignore the buoyancy correction? At 25 oC the density of water is 0.997 05 g/cm3. Solution actual volume of water dispensed by the pipet If buoyancy correction is ignored, the pipet’s volume is negative determinate error = -0.11%. 2.6 Filtration and Ignition of Solids Use a desiccator to cool a dried or ignited sample. Cool a red hot vessel before placing in the desiccator. Do not stopper a hot weighing bottlle (creates a partial vacuum on cooling). Fig. 2.16. Desiccator and desiccator plate. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Crucible Used for holding chemicals during heating to very high temperatures. Crucible Tongs Used to hold crucibles. Clay Triangle Used to support a crucible during heating.  Used to ignite samples at high temperatures, e.g., to dry ash organic matter. Fig. 2.17. Muffle furnace. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Measuring Volume Volume Measurement Volumetric flasks are calibrated to contain an accurate volume. See the inside back cover of the text for tolerances of Class A volumetric glassware. Graduated Cylinder Used to measure a precise volume of a liquid. Fig. 2.8. Volumetric flask. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Volumetric pipets accurately deliver a fixed volume. A small volume remains in the tip. Fig. 2.9. Transfer or volumetric pipets. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Measuring pipets are straight-bore pipets marked at different volumes. They are less accurate than volumetric pipets. Fig. 2.10. Measuring pipets. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Syringe pipets precisely deliver microliter volumes. They are commonly used to introduce samples into a gas chromatograph. Fig. 2.11. Hamilton microliter syringe. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) These syringe pipets can reproducibly deliver a selected volume. They come in fixed and variable volumes. The plastic tips are disposable. Fig. 2.12 Single-channel and multichannel digital displacement pipets and microwell plates. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) These accuracies and precisions are typical for single channel pipets. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) A 50-mL buret is marked in 0.1 mL increments. You interpolate to 0.01 mL, good to about ±0.02 mL. Two readings are taken for every volume measurement. Fig. 2.13. Typical buret. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  Position the black field just below the meniscus. Avoid parallax error by reading at eye level. Fig. 2.14. Meniscus illuminator. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  Place the flask on a white background. Place the buret tip in the neck of the flask while your swirl. Fig. 2.15. Proper technique for titration. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  Pipets Pipette - a high precision laboratory instruments that requires proper maintenance on a regular basis. Pipette Storage – Where and How for Pipetting Accuracy Proper storage -very important factor in maintaining an accurate pipetting result. Upright –prevent any liquids from corroding the internal workings of your pipette. Environmental Factors – Store your pipettes away from the window, heating sources and in an environment with low moisture  Ways to Stop Pipetting Errors From Ruining Your Experiments. Without accurate pipetting experiments would not be reproducible stock solutions would be inaccurate assays would have such large errors that comparing them would be meaningless. Know How Pipets Work!!! Precision instruments they may be, but the accuracy of your micropipettes depends on you Air Displacement Pipette works a bit like a syringe, except that there is an air-filled cushion between the piston and the sample. Limitations: Temperature and pressure affects the volume of the air cushion, which affects pipetting accuracy. volatile solvents can evaporate into the air cushion, which leads to an inaccurate and lower dispensed volume than what is displayed on the pipette. barrel of air displacement pipettes is vulnerable to contamination by the pipetted solution, corrosives or bio-hazardous material, this can be a problem. Positive displacement pipettes also work like a syringe, but they don’t have an air cushion—unlike air displacement pipettes. more accurate for pipetting volatile solvents because there is no place (air cushion) for the solvent to evaporate. The lack of air cushion decreases the chance of contamination when pipetting corrosives and bio-hazardous material, which makes positive displacement pipettes more suitable to working with those reagents. How do air displacement pipets work? When the push button is pressed, the piston moves down to let the air out. Volume of air displaced is equal to the volume of liquid aspirated. How do positive displacement pipets work? Works like a syringe. There is no air cushion between the disposable piston and the sample. With no elastic air cushion to expand or contract, the aspiration force remains constant, unaffected by the physical properties of the sample. This allows to pipette very viscous or high density samples such as mercury or toothpaste. Reliable results Scientists rely on pipettes that are accurate and reproducible to guarantee the success of an experiment. Factors to improve pipetting results: Physical properties of liquid: aqueous, viscous and volatile. Most liquids are of the aqueous type, making air displacement pipettes the first choice. positive displacement pipettes in very viscous or volatile liquids. Techniques for Calibrating Glassware Volumetric Flask Calibration Other Laboratory Apparatus, Glasswares and Plasticwares A fume hood is “dirty” since it draws in laboratory air. A laminar-flow hood filters air (0.3 µm HEPA filter) and flows it out into the room. Use it as a workstation for trace analysis. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Fig. 2.19. Laminar-flow workstation.  Use these for quantitative transfer of precipitates and solutions, and for washing precipitates. Fig. 2.20. Wash botltles: (a) polyethylene, squeeze type; (b) glass, blow type. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  Use for filtering non-gelatinous precipitates. Fig. 2.21. Filtering crucibles: (a) Gooch crucible; (b) sintered-glass crucible; (c) porcelain filter crucible. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Mount the filtering crucible in a crucible holder and connect the filtering flask to a water aspirator.. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  These are ashless filter papers. They are ignited away after collection of the precipitate. Use for gelatinous precipitates. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) This provides a good seal and prevents air bubbles from being drawn in. Suction from the weight of the water in the stem increases the filtration rate. Let the precipitate settle in the beaker before beginning filtration. Fig. 2.23. Properly folded filter paper. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Decant the solution by pouring down the stirring rod. After decantiing the mother liquor, add wash water to the precipitate and decant again, repeating 2-3 times. Then wash the precipitate into the filter. Fig. 2.24. Proper technique for transfer of a precipitate. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Use this to scrub the walls of the beaker and collect all the precipitate (by washing). Fig. 2.25. Rubber policeman. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Heat or ignite the crucible to a constant weight (to 0.3-0.4 mg) before adding the filtered precipitate. Fold the filter paper over the precipitate. Drive off moisture at low heat. Then gradually increase heat till the paper begins to char. After the paper is gone, ignite the precipitate. Fig. 2.26. Crucible and cover supported on a wire triangle for charring off paper. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)  Microwave ovens provide rapid drying. Acid decomposition times are reduced from hours to minutes. Lower blank levels are achieved with reduced amounts of reagents. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Fig. 2.27. Schematic of a microwave system. Use these for acid digestions. They are tilted while heating to avoid losses from “bumping”. ©Gary Christian, Fig. 2.28. Kjeldahl flasks. Analytical Chemistry, 6th Ed. (Wiley) Calibrating Volumetric Glasswares  For Volumetric Flasks Weigh out a dry and clean volumetric flask Fill it to the mark with boiled distilled water at room temperature Measure the weight of the flask and record the temperature of water it contains. Calculate the volume of the flask V (in ml) = (w1 – w2) + f (w1 – w2) In which: w1 = weight of the filled flask in grams w2 = weight of the empty flask in grams f = correction factor (see table 1)  For Pipettes Fill the pipette with boiled water that is at room temperature Dry the tip with a tissue. Let water flow away until the lowest part of the meniscus touches the mark. Let the tip of the pipette be held against the inner wall of the vessel at an angle of 45 degrees. Collect contents in a preweighed weighing bottle. Repeat procedure four times and measure the temperature of water used. Calculate the standard volume of the pipette V (in ml) = (w1 – w2) + f (w1 – w2) In which:w1 = weight of the filled weighing bottle (gram) w2 = weight of the empty weighing bottle (gram) f = correction factor  For Burettes Fill the burette with boiled water that is at room temperature until water stands 1 cm above zero point Adjust the lowest part of the meniscus so that it touches the zero mark Remove all drops that cling to the inner wall of the burette using a filter paper. Remove any drops at the tip of the burette by touching it against the wall of the vessel. Run off the contents into a preweighed bottle until the predetermined graduation is reached. Collect the last drop from the tip of burette Measure the weight and temperature of the water used Repeat procedure for other checkpoints Calculate the standard volume of the burette V (in ml) = (w1 – w2) + f (w1 – w2) In which:w1 = weight of the filled weighing bottle (gram) w2 = weight of the empty weighing bottle (gram) f = correction factor  Techniques for Calibrating Glassware Pipet Calibration 1. Weigh a clean, dry conical flask with a rubber stopper or a weighing bottle with a glass stopper or cap. 2. Fill pipet with distilled water and deliver the water into the flask or bottle, stopper container to avoid evaporation loss. Record temperature to 0.1oC 3. Reweigh the container to obtain the weight in air of the water delivered by the pipet.  Techniques for Calibration of Glassware Buret Calibration 1. Weigh a clean, dry conical flask. 2. Take the volume at 20% full-volume increments by filling the buret each time and then delivering the nominal volume into a dry flask. 3. Alternative: make successive deliveries into same flask, filling the buret only once. 4. The delivered volume does not have to be exact, but close to the nominal volume, you can make fairly fast deliveries, but wait 10 to 20s for film drainage. 5. Prepare a plot of volume correction versus nominal volume and draw straight lines between each point. Interpolation is made at intermediate volumes from the lines. 2.2. Cleaning and Marking of Laboratory Ware 2.2.1 Marking of Laboratory ware Grease pencils or wax pencils are used to mark glassware when doing simultaneous experiments. Special marking inks are used for or permanently marking laboratory porcelain. The marking is baked permanently into the glazed by heating at a high temperature. A saturated solution of Iron Chloride can also be used for marking. Cleaning Laboratory Glassware Wash labware as quickly as possible after use. If labware is not cleaned immediately, it may become impossible to remove any residue. For precision chemical testing, new glassware should be soaked for several hours in acid water (a 1% solution of hydrochloric or nitric acid) before proceeding with a regular washing procedure. Borosilicate glassware (Pyrex, Kimax) is normally used because it is thermally stable. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Organic Chemistry Laboratory Techniques | Nichols | Organic Chemistry Laboratory Techniques | Nichols | Organic Chemistry Laboratory Techniques | Nichols | Microscale chemistry -experiments using small quantities of chemicals and simple equipment. Advantages: - reduce costs - reduce safety hazards - allow many experiments to be done quickly and sometimes outside of the laboratory. https://www.stem.org.uk/resources/collection/4034/microscale- chemistry Organic Chemistry Laboratory Techniques | Nichols | Most organic glassware uses “ground glass joints,” which have a frosted appearance. Common joint sizes are 14/20, 19/22, and 24/40. The first number refers to the inner diameter (mm) of a female joint or outer diameter of a male joint. The second number refers to the length of the joint (Figure 1.1b). Organic Chemistry Laboratory Techniques | Nichols |  It is best if ground glass joints are free of chemicals when pieces are connected, or else the compounds may undergo reactions that cause the joints to “freeze” together, or become inseparable. Solid in the joint can also compromise the seal between the pieces. Lint-free If chemical residue were to get on the joint Lint -- short fibres included in some during transfer (Figure 1.1c), the joint fabrics. As time passes, these fibres will should be wiped clean with a KimWipe (lint- loosen up and eventually appears on the free tissue surface. Figure 1.2a) before connecting with another - can be found in cotton, wool, linen, and other types of fabrics. Typically, lint piece. Spillage on the joint can be minimized free cloth is the best choice by using a funnel. Organic Chemistry Laboratory Techniques | Nichols | Figures 1.2 b+c shows a “frozen” joint (residue on the frosted joint), benzaldehyde crept into the joint during storage and oxidized to seal the round bottomed flask. To separate a frozen joint: 1. Gently twist the two pieces apart from one another. 2. If that fails, gently tap on the joint with a spatula or other piece of equipment (Figure 1.2c). 3. If that fails, next try heating the joint in a hot water bath (heat may cause expansion of the outer joint), or sonicating the flask if a sonicator is available. 4. As a last resort, heat the joint briefly with a heat gun. The frozen joint in Figure 1.2 had to be heated to separate the pieces. Organic Chemistry Laboratory Techniques | Nichols | CLAMPING It is important that the pieces are securely fastened in an apparatus so that flammable vapors don’t escape and pieces don’t fall (whereupon the glassware may break or contents may be spilled). Organic Chemistry Laboratory Techniques | Nichols |  2 common type of clamps are “extension clamps” and “three- fingered clamps” (Fig. 1.4a). An extension clamp must be used when clamping to a round bottomed flask (Fig 1.4b), as 3-fingered clamps do not hold well. The extension clamp should securely grasp the neck of a round bottomed flask below the glass protrusion (Fig. 1.4b, not Fig. 1.4c). Organic Chemistry Laboratory Techniques | Nichols | Three fingered clamps are generally used to hold condensers (Fig 1.3b), suction flasks, and chromatography columns (Fig. 1.5). Organic Chemistry Laboratory Techniques | Nichols | Ring clamps (or iron rings) are also commonly used in the organic lab. -used to hold separatory funnels (Fig. 1.6a) -can be used to secure funnels when filtering or pouring liquids into narrow joints (Fig. 1.6b). -can be used along with a wire mesh to serve as a platform for supporting flasks (Figure 1.6c). Organic Chemistry Laboratory Techniques | Nichols | Plastic clips (sometimes called “Keck clips” or “Keck clamps”) are used to secure the connections between joints (Fig. 1.7). Plastic clips should not be used on any part of an apparatus that will get hot, as they may melt at temperatures above 140 ˚C (Fig. 1.7b). Metals versions of these clips can be used alternatively in hot areas. Reaction flasks should not be held with just Clips should not be relied upon to hold clips, but always supported in some more any substantial weight, as they can easily significant way (e.g. with an extension clamp fail (especially if they have been attached to a ring stand). warmed). GREASING JOINTS Grease is also used whenever the joint may be in contact with a highly basic solution, as basic solutions can form sodium silicates and etch glass. Grease can be applied with a syringe full of If grease is allowed near the end which grease (Fig 1.8a), wood splint, or toothpick. will contact the reagents, there is a Grease should be lightly applied in portions possibility the reagent will dissolve the around the male joint, closer to the glass end grease and become contaminated. The than the end which will be in contact with the female joint should then be connected, reagents (Fig 1.8a). and the joints twisted to spread the grease in a thin layer To clean grease from a joint after a process is complete, wipe off the majority of the grease using a paper towel or Kimwipe. Then wet a KimWipe with some HC solvent and rub the moistened KimWipe onto the joint to dissolve the grease (Fig 1.9). HC solvents (e.g. hexanes) work much better than acetone to dissolve residual grease.  CLEANING GLASSWARE Glassware should be dismantled and cleaned as soon as possible. If there is a time constraint, it’s best to leave glassware in a tub of soapy water. To clean glassware, use the following procedures: Use 2-3 mL solvent to rinse residual organic compounds from the glassware into a waste beaker. The compounds should be highly soluble in the solvent. The default solvent is often acetone as it is inexpensive, relatively nontoxic, and dissolves most organic compounds. Some reuse acetone (“wash acetone”) as the solvation ability is not spent after a few uses. Purpose of an acetone rinse is to dissolve organic residue in a flask. Not everything dissolves in acetone, for example ionic salts are insoluble in acetone and are more successfully rinsed out with water.  After a preliminary rinse, glassware should then be washed with soap and water at the bench. Residual acetone will likely evaporate from the flask, but it is acceptable for small quantities of residual acetone to be washed down the drain. If using undiluted detergent from the store, it is best to use small amounts during washing as they tend to form thick foams that need lots of rinsing). Some use dilute soap solutions at their cleaning stations for this reason. For cleaning of glassware, the biodegradable detergent “Alconox” is the industry standard. Rinse all glassware with a few mL of distilled water, then store wet glassware in a locker atop paper towels to evaporate by the next lab period.  Drying QUICK DRYING If dry glassware is not needed right away, it should be rinsed with distilled water and allowed to dry overnight (in a locker). If dry glassware is promptly needed, glassware can be rinsed with acetone and the residual acetone allowed to evaporate. Rinsing with acetone works well because water is miscible with acetone, so much of the water is removed in the rinse waste. Evaporation of small amounts of residual acetone can be expedited by placing the rinsed glassware in a warm oven for a short amount of time or by using suction from a tube connected to the water aspirator. Residual acetone should not be evaporated inside a hot oven (> 100 ˚C) as acetone may polymerize and/or ignite under these conditions.  OVEN AND FLAME DRYING Glassware that appears “dry” actually contains a thin film of water condensation on its surface. When using reagents that react with water (sometimes violently!), this water layer needs to be removed. To evaporate the water film, glassware can be placed in a 110 ˚C oven overnight, or at the least for several hours. The water film can also be manually evaporated using a burner or heat gun, a process called “flame drying.”  To flame dry glassware, first remove any vinyl sleeves on an extension clamp (Fig 1.11a), as these can melt or catch on fire. Clamp the flask to be dried. Apply the burner or heat gun to the glass, and initially fog will be seen as water vaporizing from one part of the glassware condenses. Continue waving the heat source all over the glassware for several minutes until the fog is completely removed and glassware is scorching hot. If the glass is only moderately hot, water will Regardless of the manner in condense from the air before you are able to fully which glassware is heated (oven exclude it. or flame drying), allow the glassware to cool in a water-free Safety Note: glassware will be extremely hot after environment (in a desiccator, flame drying under a stream of inert gas, or with a drying tube 0before obtaining a mass or adding reagents.  STORING SAMPLES (PARAFILM / TEFLON TAPE) When samples must be stored for a period of time, they are best stored upright in screw-capped vials: Use Teflon tape or Parafilm (stretchy plastic film) to create a better seal. Teflon tape is less permeable to solvents than Parafilm volatile samples wrapped in Parafilm may still evaporate over a period of weeks.  TRANSFERRING METHODS Solids a “powder funnel” or wide-mouth funnel can be used (Figure 1.15a). the solid can be nudged off a creased piece of paper in portions using a spatula (Figures 1.15 b+c). If the solid is the limiting reagent in a chemical reaction, it should be dispensed from the reagent jar directly into the vessel. if using a weighing boat, residue should be rinsed off with the solvent that will be used in the reaction (only if the boat is unreactive to the solvent) in order to transfer the reagent in its entirety.  Residue clinging to ground glass joints should also be dislodged with a KimWipe or rinsed into the flask with solvent to prevent joints from sticking, and to make sure the entire reagent makes it to the reaction vessel. Some solid compounds (e.g. KOH, K2CO3, CaCl2) are sticky or hygroscopic (readily absorb water from the air), and these reagents should be dispensed onto glossy weighing paper that has a wax coating so that sticky reagents more easily slide off its surface. For transfer into vessels with very narrow mouths (e.g. NMR tubes), it is sometimes easier to dissolve solids in their eventual solvent and transfer a solution via pipette (Figures 1.16 b+c).  POURING LIQUIDS When transferring liquids with volumes > 5 mL, they can be poured directly into vessels. Graduated cylinders and beakers have an indentation in their mouth, so they can be poured controllably as long as the two pieces of glass touch one another. If pouring from an Erlenmeyer flask, or transferring a liquid into a vessel containing a narrow mouth (e.g. a round bottomed flask), a funnel should be used. Funnels can be securely held with a ring clamp or held with one hand while pouring with the other (Figure 1.17c).  When determining the mass of a vessel on a balance, it’s best to not include the mass of a cork ring or other support (e.g. the beaker in Figure 1.18b). A cork ring might get wet, have reagents spilled on it, or have pieces of cork fall out, leading to changes in mass that cannot be accounted for. Beakers used to support flasks can get mixed up, and every 100-mL beaker does not have the same mass. It is also best to transport vessels containing chemicals to the balance in sealed containers, so as to minimize vapors and prevent possible spillage during transport.  USING PASTEUR PIPETTES Pasteur pipettes are the most commonly used tool for transferring small volumes of liquids (< 5 mL) from one container to another. They are considered disposable, although some may clean and reuse them if they have a method for preventing the fragile tips from breaking.  Pasteur pipettes come in two sizes (short 5.75”) and long (9”). Each can hold about 1.5 mL of liquid, although the volume delivered is dependent on the size of the dropper bulb. General guideline: “1 mL is equivalent to 20 drops” does not always hold for Pasteur pipettes, and may be inconsistent between different pipettes.  Using CALIBRATED PLASTIC PIPETTES How To use: withdraw some of the liquid to be transferred into the bulb as usual (b). squeeze the bulb just enough so that the liquid drains to the desired volume (c), and maintain your position. While keeping the bulb depressed so the liquid still reads to the desired volume, quickly move the pipette to the transfer flask (d), and depress the bulb further to deliver liquid to the flask (e) Calibrated plastic pipettes have markings at 0.25 mL increments for a 1 mL pipette, and are economical ways to dispense relatively accurate volumes.  Using CALIBRATED GLASS PIPETTES When a high level of precision is needed calibrated glass pipettes (volumetric or graduated) can be used. Volumetric pipettes have a glass bulb at the top of their neck, and are capable of dispensing only one certain volume. Graduated pipettes (Mohr pipettes) have markings that allow them to deliver many volumes. Both pipettes need to be connected to a pipette bulb to provide suction. The volume markings on a graduated pipette indicate the delivered volume.  The left-most pipette has markings every 0.1 mL, but no intermediary markings so is less precise than the other two pipettes (a). The other two pipettes differ in the markings on the bottom. The lowest mark on the middle pipette is 1 mL, while the lowest mark on the right-most pipette is 0.9 mL. To deliver 1.00 mL with the middle pipette, the liquid must be drained from the 0.00 mL to the 1.00 mL mark, and the final inch of liquid should be retained. To deliver 1.00 mL with the right-most pipette, liquid must be drained from the 0.00 mL mark completely out the tip, with the intent to deliver its total capacity.  Pipettes are calibrated “to-deliver” (TD) or “to- contain” (TC) the marked volume. Pipettes are marked with T.C. or T.D. to differentiate between these two kinds, and to- deliver pipettes are also marked with a double ring near the top (b). After draining a “to-deliver” pipette, the tip should be touched to the side of the flask to withdraw any clinging drops, and a small amount of residual liquid will remain in the tip. A “to-deliver” pipette is calibrated to deliver only the liquid that freely drains from the tip. After draining a “to-contain” pipette, the residual liquid in the tip should be “blown out” with pressure from a pipette bulb. “To-contain” pipettes may be useful for dispensing viscous liquids, where solvent can be used to wash out the entire contents.  T.C. pipette--use pressure from a pipette bulb to blow out the residual drop. Do not blow out the residual drop when using a T.D. pipette. If volumetric pipette is used, the liquid should be withdrawn with suction to the marked line above the glass bulb (d). The liquid can be drained into the new container with your finger fully released from the top. When the liquid stops draining, the tip should be touched to the side of the flask to withdraw any clinging drops, but the residual drop should not be forced out (similar to a T.D. pipette). CALIBRATED PIPETTES SUMMARY DISPENSING HIGHLY VOLATILE LIQUIDS When attempting to dispense highly volatile liquids (e.g. diethyl ether) via pipette, it is very common that liquid drips out of the pipette even without pressure from the dropper bulb! This occurs as the liquid evaporates into the pipette’s headspace, and the additional vapor causes the headspace pressure to exceed the atmospheric pressure. To prevent a pipette from dripping, withdraw and expunge the liquid into the pipette several times. Once the headspace is saturated with solvent vapors, the pipette will no longer drip. POURING HOT LIQUIDS It may be difficult to manipulate a vessel of hot liquid with your bare hands. If pouring a hot liquid from a beaker, a silicone hot hand protector can be used (a) or beaker tongs (b+c). Pouring from hot Erlenmeyer flasks can be accomplished using a makeshift “paper towel holder.” METHODS AND FLAMMABILITY Not all organic liquids will immediately ignite if placed near a heat source. Many liquids require an ignition source (a spark, match, or flame) in order for their vapors to catch on fire, a property often described by the liquid’s flash point. The flash point is the temperature where the vapors can be ignited with an ignition source. For example, the flash point of 70% ethanol is 16.6 ˚C, 2 meaning it can catch on fire at room temperature using a match.  Important property in flammability is a liquid’s autoignition temperature: the temperature where the substance spontaneously ignites under normal pressure and without the presence of an ignition source. This property is particularly insightful because it does not require a flame (which is often avoided in the organic lab), but only a hot area. A hotplate surface turned up to “high” can reach temperatures up to 350 ˚C.  Important property in flammability is a liquid’s autoignition temperature: the temperature where the substance spontaneously ignites under normal pressure and without the presence of an ignition source. This property is particularly insightful because it does not require a flame (which is often avoided in the organic lab), but only a hot area. A hotplate surface turned up to “high” can reach temperatures up to 350 ˚C.  Important property in flammability is a liquid’s autoignition temperature: the temperature where the substance spontaneously ignites under normal pressure and without the presence of an ignition source. This property is particularly insightful because it does not require a flame (which is often avoided in the organic lab), but only a hot area. A hotplate surface turned up to “high” can reach temperatures up to 350 ˚C. Safety note: as diethyl ether, pentane, hexane, and low-boiling petroleum ether have autoignition temperatures below this value (Table 1.7), it would be dangerous to boil these solvents on a hotplate as vapors could spill out of the container and ignite upon contact with the surface of the hotplate. Caution should be used when using a hotplate for heating any volatile, flammable liquid in an open vessel as it’s possible that vapors can overrun the hotplate’s ceramic covering and contact the heating element beneath, which may be hotter than 350 ˚C. It is for this reason that hotplates are not the optimal choice when heating open vessels of volatile organic liquids, although in some cases they may be used cautiously when set to “low” and used in a well-ventilated fume hood. As combustion is a reaction in the vapor phase, liquids with low boiling points (< 40 ˚C) tend to have low flash points and autoignition temperatures as they have significant vapor pressures (Table 1.7). All low boiling liquids should be treated more cautiously than liquids with moderate boiling points (> 60 ˚C). The Laboratory Notebook  Lab Notebooks It’s a notebook, not a neat book  Bad record-keeping costs. LeMonnier, French astronomer who gets no credit for the first sightings of the planet Uranus. His notes were so bad that he thought it was a comet. Discovery of Uranus is instead awarded to Herschel. Gordon Gould had many ideas related to the production and use of lasers. He foresaw that they could cut steel or ignite fusion reactions. His notes were witnessed by a candystore notary instead of a colleague. He had undocumented meetings with the “maser people.” Years and years of legal proceedings were required to get him some of the credit he deserved.  Types of Documentation Notebook—factual details of experiments, including thought experiments, ideas, inventions, etc. Logbook—for example, a list of measurements made on the NMR, Balance, etc. Diary (Journal)—What you were feeling, a personal record, opinions—stuff that is less factual than the notebook. Depending on the situation, this might be appropriate to place in the notebook but be careful to delineate fact from opinion.  Computer Records This is a whole industry now—LIMS , Laboratory notebooks. Example: balances or pH meters that are hooked into a database. A few misguided souls have almost stopped keeping written records. We operate on the assumption that you are not misguided, so DO keep a decent lab notebook. Back up your data! Good Laboratory Practice (GLP) requires that you PROTECT THE RAW DATA. If you need to edit something, save a COPY of the raw data.  A proper notebook page Written as the work is performed Dated and signed by author Each section has a clear, descriptive heading The writing is legible and grammatically correct Active voice in first person: “I added the two ingredients…” Read by witness and signed/dated Do Not write over; cross, and write above  The Right Stuff Notebooks have to last 23 years after patent issue. Patents take time to get, so figure 30 years longevity. Paper has to be very good (much paper today is junk by the standards of a hundred years ago). Notebook should be bound. No spiral notebooks! No loose-leaf! Page layout easy to graph, date, sign, etc. Table of contents!  What to write with? No pencils.* Erasures are a definite no-no! No aqueous-based pens (e.g., most felt-tips). Best bet for general use: black, ballpoint pen. No white-out!! Just strike through, explain and initial errors. “It’s a notebook, not a neat book.”—R. Cueto *There are some exceptions—e.g. field notebooks where you know it will get wet and may not have a ready supply of pens.  Sticky situations It is better to glue or tape that original paper snippet into the lab book than it is to copy the result. Glue: acid-free white glue is best. (Elmer’s?) Rubber cement is not recommended (but used to be) Tape: Archival mending tape is recommended. There are various qualities of tape (3M?).  Legal Matters When you are working with an employer, you do NOT own the no You may ask for a copy. The lab head can and should inspect books periodically.  What goes in the notebook? Plans Realities (deviations from the plan) Observations Sketches and photographs “Links” to the notebooks of others in your group “Links” to instrument logbooks and data on disks Ideas: a notebook is a repository of creativity E-mails from collaborators (tape or paste them in) Plot-as-you-go graphs: do it! Summaries of papers you have read Hints and tips you may get from science friends Concerns and personal data….but be careful to delineate fact from fiction/opinion. Also, remember that personal info could become embarrassingly public! For that, use a diary.  Plan your activities in the laboratory so that all information is properly entered into the notebook while you are in the laboratory. Include in the notebook a complete description of the work performed, all reference materials consulted, and ideas that you have related to the work. There should be no loose scraps of paper in the notebook. Graphs, charts, spectra, or spreadsheet analyses should be affixed to the pages of the notebook with tape or glue. Label the space where this material is to go with a description of the item and the results it contained.  It is critical that the material is intelligible and understandable to the notebook author and any trained chemist who reads the records, attempts to reproduce these results, or endeavors to finish an incomplete analysis. This concept is often known as “traceable” in the industrial world.  If a page is skipped, a large “X” must be drawn across it. The page is then initialed and dated. If an error is made, draw a single bold horizontal line through the error so that it can still be read. Write the correct information to the right of the incorrect entry. Never use whiteout or completely obliterate the incorrect entry. References: Christian, G.D. (2003). “Analytical Chemistry,” 6th Edition https://chemlab.truman.edu/the-laboratory-notebook/ Reflux. (2021, June 3). Retrieved June 5, 2021, from https://chem.libretexts.org/@go/page/93228 https://www.orgchemboulder.com/Technique/Procedures/SolventRemoval/SolventRemoval.shtml https://chemdictionary.org/steam-distillation/ https://slidetodoc.com/operations-of-analytical-chemistry- chemicals-apparatus-units-and/