Volumetric flasks calibration

The United States Pharmacopoeia (USP) requirements for volumetric flasks calibrated to contain the indicated volume at 25°C are given in Table 2.7. 

Ans. Weigh out 26.75 g (0.5 mol) of the salt, and dissolve it in sufficient water so that the final volume of solution is one liter. The dilution is done in a volumetric flask calibrated to contain 1000 mL. 

Alkaloid Standard Solution and Calibration Curve. Morphine (10 mg), the-baine (2mg), papaverine (2mg), codeine (2mg), crytopine (2mg), and narcotine (6 mg) are dissolved in methanol and made up to 5 ml in a volumetric flask. Calibration curve for each alkaloid is prepared by injecting varying amounts (microliters) of standard solutions into the liquid chromatograph, and measuring the peak height against the amount injected. 

Suppose we prepare a solution at 20 °C by using a volumetric flask calibrated at 20 °C. Then suppose we warm this solution to 25 °C. As the temperature increases from 20 to 25 °C, the amount of solute remains constant, but the solution volume increases slightly (by about 0.1%). The number of moles of solute per liter—the molarity—decreases slightly (by about 0.1%). This temperature dependence of molarity can be a problem in experiments demanding a high precision. That is, the solution might be used at a temperature different from the one at which it was prepared, and so its molarity is not exactly the one written on the label. A concentration unit that is independent of temperature, and also proportional to mole fraction in dilute solutions, is molality (m)—the number of moles of solute per kilogram of solvent (not of solution). A solution in which... 

Pipets and volumetric flasks provide a more accurate means for measuring volume. When filled to its calibration mark, a volumetric flask is designed to contain a specified volume of solution at a stated temperature, usually 20 °C. The actual vol-... 

Three important precautions are needed when working with pipets and volumetric flasks. First, the volume delivered by a pipet or contained by a volumetric flask assumes that the glassware is clean. Dirt and grease on the inner glass surface prevents liquids from draining evenly, leaving droplets of the liquid on the container s walls. For a pipet this means that the delivered volume is less than the calibrated volume, whereas drops of liquid above the calibration mark mean that a volumetric flask contains more than its calibrated volume. Commercially available cleaning solutions can be used to clean pipets and volumetric flasks. 

Second, when filling a pipet or volumetric flask, set the liquid s level exactly at the calibration mark. The liquid s top surface is curved into a meniscus, the bottom of which should be exactly even with the glassware s calibration mark (Figure 2.6). The meniscus should be adjusted with the calibration mark at eye level to avoid parallax errors. If your eye level is above the calibration mark the pipet or volumetric flask will be overfilled. The pipet or volumetric flask will be underfilled if your eye level is below the calibration mark. 

To prepare the solution we measure out exactly 0.1500 g of Cu into a small beaker. To dissolve the Cu we add a small portion of concentrated HNO3 and gently heat until it completely dissolves. The resulting solution is poured into a 1-L volumetric flask. The beaker is rinsed repeatedly with small portions of water, which are added to the volumetric flask. This process, which is called a quantitative transfer, ensures that the Cu is completely transferred to the volumetric flask. Finally, additional water is added to the volumetric flask s calibration mark. 

Calculate the molarity of a potassium dichromate solution prepared by placing 9.67 g of K2Cr207 in a 100-mF volumetric flask, dissolving, and diluting to the calibration mark. 

To dilute a stock solution to a desired concentration, we first use a pipet to transfer the appropriate volume of stock solution to a volumetric flask, a flask calibrated to contain a specified volume. Then we add enough solvent to increase the volume of the solution to its final value. Toolbox G.l shows how to calculate the correct initial volume of stock solution. 

Weigh 0.1000 g of analytical standard NIPA into a 100-mL volumetric flask, dilute the standard to volume with isooctane-ethyl acetate (9 1, v/v), and mix the solution well. This solution contains 1000 qg mL of the analyte. Dilute the solution as appropriate to prepare calibration standards at the following concentrations 0.01, 0.025,0.05,0.10, 0.25,0.50,0.75, and 1.00 qgmL Store all standards refrigerated (0-6°C) in amber-glass bottles. 

Stock solutions of approximately 1 mg mL were prepared by dissolving the appropriate amounts of the analytical standards in acetonitrile. Working standard solutions for fortification were prepared in volumetric flasks by appropriate dilutions of the stock solutions for each analyte or combination of analytes. During analysis, SCA is converted to DMS and HMS is derivatized therefore, the analytical standard solutions for quantitation and instrument calibration contained sulfentrazone, DMS and derivatized HMS. A measured volume of a standard solution containing sulfentrazone, DMS and HMS (prepared from stock solutions) was derivatized simultaneously with the samples. 

After refluxing, disconnect the trapping tube, and transfer the yellow solution into a 25-mL volumetric flask. Rinse the mbe with ethanol, and adjust the solution to volume with ethanol. Measure the absorbance of the solution at 435 nm against a blank prepared by diluting 15 mL of color reagent to 25 mL with ethanol. Determine the carbon disulflde content from a calibration curve obtained by plotting carbon disulfide concentrations of different standard solutions on the abscissa versus the absorbance on the ordinate. 

Ninhydrin Assays. Ninhydrin tests were performed using a modified procedme of Taylor et al. " APS Silica (10-75 mg) of various loadings (0.857, 0.571, and 0.343 mmol NH2/g Silica) was added to phosphate buffer (5 mL, 100 mM, pH 6.5), and 1 mL of a 5% w/v solution of ninhydrin in ethanol was added to the sluny. After stirring for an hour in a boiling water bath, the mixture was allowed to cool slowly to room temperature. The silica was then filtered and washed three times with 70°C distilled water. The filtrate was collected, added to a volumetric flask, diluted to 100 mL, and the absorbance of this solution at 565 mu was measured using a UV-visible spectrophotometer. The reference solution was prepared as above with unmodified amine-free silica. Calibration standards were prepared with aliquots of a 1 mg/mL solution of APS in ethanol. 

Weigh out 29.22 g of NaCl and dissolve it in a portion of water in a 250-mL volumetric flask (Fig. 10-2). After the salt has dissolved, dilute the solution with water until the volume reaches the calibration mark on the flask (250.0 mL). Mix the solution thoroughly by inverting and shaking the stoppered flask several times. 

What is essential in establishing traceability is that the measurand is specified unambiguously. This may be, e.g. in terms of extractable cadmium from soil by using a named acid mix or the concentration of a metal in a particular oxidation state, e.g. Fe(n) or Fe(m). The units used to report the result should also be known and acceptable SI units are preferred. The method used will be validated and if used in accordance with the written procedures should produce results that are fit for purpose . The class of glassware to be used will be specified in the method procedure, e.g. Class A pipettes and volumetric flasks, as these are manufactured to a specified tolerance. Instruments will be regularly calibrated and their performance verified daily. In terms of the chemicals used, these will... 

About 0.1-2.0g of wet sediment was placed into a Teflon vessel and 3mL of concentrated nitric acid, 0.5mL concentrated perchloric acid, and 4mL concentrated hydrofluoric acid were added. The closed vessels were kept at room temperature for lh. The samples were then placed in a pressure cooker and heated for lh on a hot plate at a temperature of 300°C. After cooling, the vessels were uncapped and the samples evaporated to 2mL on a hot plate at 250°C. After cooling, 3mL concentrated nitric acid was added. To complex the fluorides, lg boric acid was added to each sample. The solutions were transferred to lOOmT volumetric flasks and adjusted to volume with deionized water. Inorganic arsenic standards, having the same acid content as the samples, were used for calibration. 

FIGURE 4.3 Left, a 1000-mL volumetric flask. Right, a close-up view of the neck of the flask showing the single calibration line. 

As indicated previously, most pipets are pieces of glassware that are designed to deliver (TD) the indicated volume. Pipets come in a variety of sizes and shapes. The most common is probably the volumetric pipet, or transfer pipet, shown in Figure 4.8. This pipet, like the volumetric flask, has a single calibration... 

Some pipets are calibrated TC. Such pipets are used to transfer unusually viscous solutions such as syrups, blood, etc. With such solutions, the wetness remaining inside after delivery is a portion of the sample and would represent a significant nontransferred volume, which translates into a significant error by normal TD standards. With TC pipets, the calibration line is affixed at the factory so that every trace of solution contained within is transferred by flushing the solution out with a suitable solvent. Thus, the pipetted volume is contained within and then quantitatively flushed out. Such a procedure would actually be acceptable with any TC glassware, including the volumetric flask. Obviously, diluting the solution in the transfer process must not adversely affect the experiment. 

Prepare calibration standards of 1.0,2.0,3.0, and 4.0 ppm iron from the 100 ppm stock in 50-mL volumetric flasks, but do not dilute to the mark until step 6. Also prepare a flask for the blank (no iron). If real water samples are being analyzed and you expect the iron content to be low, prepare two additional standards that are 0.1 and 0.5 ppm. 

Prepare four calibration standards that are 0.1, 0.5, 1.0, and 1.5 ppm P from the stock standard prepared in step 6. Use 100-mL volumetric flasks. 

Prepare four calibration standards with concentrations of 0.0435,0.0870,0.174, and 0.261 g/L in the alkane solvent by diluting the stock solution prepared in step 1. Use the 25-mL volumetric flasks prepared in step 1. 

Prepare calibration standards that are 0.5, 1.0, 3.0, 5.0, and 10.0 ppm N in 50-mL volumetric flasks by diluting the stock standard with distilled water. After diluting to the mark, pipet 1.0 mL of 1 N HC1 into each flask and shake well. 

Your instructor has prepared a 50 ppm riboflavin stock solution in 5% (by volume) acetic acid. Prepare a series of calibration standard solutions that are 0.2, 0.4, 0.6, 0.8, and 1.0 ppm from the 50 ppm stock solution and again use 5% acetic acid for the dilution. Use 25-mL volumetric flasks for these standards and shake well. 

In dry 25-mL volumetric flasks, prepare four calibration standards of isopropyl alcohol in toluene solvent that are 20, 30, 40, and 50% in alcohol concentration. Obtain an unknown from your instructor and dilute to the mark with toluene. Shake well. 

Prepare calibration standards that are 0.05, 0.10, 0.15, and 0.20 mg/mL in caffeine from the stock standard. Use 25-mL volumetric flasks and measuring pipets or pipetters suggested by your instructor. Calculate the concentration of sodium benzoate in each of these solutions. 

A volumetric flask is a precision piece of glassware with a single calibration line in a narrow neck An Erlenmeyer is not a precision piece of glassware and has graduation lines on it only as a rough indication of volume. 

The final concentration of each reactant is calculated from the final volume and the volume and concentration of the solution pipeted into the volumetric flask. The calibration curve is used to find the equilibrium concentration. Using the balanced chemical equation, the equilibrium concentrations of the other substances may be calculated. 

In a similar manner, the calibration of glassware, such as volumetric flasks, pipettes, burettes, measuring cylindres are duly carried out by specific methods recommended by Indian Standards Institution (ISI), British Standards Institution (BSI), National Physical Laboratory (NPL), United States Pharmacopoeia (USP) at specified temperatures (See Chapter 2). 

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