Laboratory Safety and Chemical Handling: Rules, Disposal, and Equipment, Lab Reports of Quantitative Techniques

Download Laboratory Safety and Chemical Handling: Rules, Disposal, and Equipment and more Lab Reports Quantitative Techniques in PDF only on Docsity! Safety “The primary safety rule is to familiarize yourself with the hazards and then to do nothing that you (or your instructor or supervisor) consider to be dangerous.” Follow the laboratory safety rules. Proper waste handling and disposal Know how to properly handle and dispose of chemicals you use in the lab. Don’t pour anything down the drain without first knowing if it is safe to do so and is not going to be harmful to the people or the environment. Reading: Chapter 2 183.9 74 The Tools CHEM 3000, Quantitative Analysis Some options for disposal: Pour solutions down the drain with plenty of water Saving the waste for later disposal Treating the waste to decrease the hazard and then pouring it down the      drain or save. Recycle! Label all vessels to indicate the contents!!! Material Safety Data Sheets (MSDS) provide information on hazards and safety precautions. Every chemical sold in the U.S. has one!! The MSDS may include the following sections: Chemical product identification Composition Hazards identification First aid measures Fire and explosion information Accidental release Handling and storage Exposure controls Physical and chemical properties Stability and reactivity The tolerance values represent the maximum allowed deviation for the respective standard masses. Periodically check the calibration with a standard mass to determine if it is within the allowed tolerance Buoyancy An object that displaces a particular volume of air will have an apparent mass less that the actual mass. The difference is equal to the mass of the displaced air. Correction is needed when the density of the object being weighed is different from the density of the standard calibration weights: 8.0 g/mL m is the actual mass if weighed in vacuum, m′ is the balance reading, da is the density of air (0.0012 g/mL at ~1 bar & 25oC), dw is the density of the calibration weights, and d is the density of the object being weighed. The apparent mass measured in air is multiplied by the buoyancy correction to determine the true mass: Relative error: 25 mL from a 50-mL buret vs. a 100-mL buret…. Volumetric Flasks Calibrated to contain a particular volume of solution at 20°C when bottom of the meniscus is adjusted to the center of mark on the neck of the flask. Dissolve the desired mass of reagent in the flask and swirl with LESS than the final volume of liquid Add additional liquid & swirl Adjust final volume of the MIXED solution to the calibration mark For good control, add final drops with a pipet – squirt bottle is usually not the best Invert the flask several times!!! Invert any container before usingany solution!! Glass adsorbs traces of chemicals – especially cations For very critical work (a good idea every so often), you should acid wash glassware to replace cations with H+. (Soak cleaned flask in 3 – 6 M HCl for > hr. Rinse with DI water. Soak in DI water. Use acid over again.) For very trace cations analysis, use polypropylene volumetric flasks Pipets & Syringes (a) Transfer pipet designed to deliver (“TD”) one fixed volume. The last drop should NOT be blown out!! (b) Measuring pipet designed to deliver a variable volume. To deliver 5.6 mL you start at the 1.0 mL mark and stop at the 6.6 mL mark. Rinse pipet a couple of times Draw up a third volume. Wipe off excess liquid with tissue Touch the tip of the pipet to the side of container and drain the liquid until the bottom of the meniscus just reaches the center of the mark. This allows the liquid to drain without leaving part of a drop hanging when the liquid reaches the mark Table 2-5 Manufacturer’s tolerances for micropipets At 10% of pipet volume At 100% of pipet volume Pipet volume (ul) Accuracy (%) — Precision (%) Accuracy(%) — Precision (%) Adjustable Pipets 0.2-2 +8 +4 +1.2 +0.6 1-10 #2.5 +1.2 +0.8 +0.4 2.5-25 +45 +1.5 +0.8 +0.2 10-100 +1.8 +0.7 +0.6 +£0.15 30-300 +1.2 +0.4 +0.4 +0.15 100-1 000 +1.6 +0.5 +0.3 +£0.12 Fixed Pipets 10 +0.8 +0.4 25 +0.8 +0.3 100 +0.5 +0.2 500 +0.4 +0.18 1000 +0.3 +0.12 SOURCE: Data from Hamilton Co., Reno. NV. Table 2-5 Quantitative Chemical Analysis, Seventh Edition © 2007 W.H. Freeman and Company Filtration Separation of precipitates from the liquid for gravimetric analysis Gooch crucible with suction... Conical funnel with filter paper.... Filtration + ignition using ashless filter paper...