Pipet volumetric

A 10-mL volumetric pipet was calibrated following the procedure just outlined, using a balance calibrated with brass weights having a density of 8.40 g/cm. At 25 °C the pipet was found to dispense 9.9736 g of water. What is the actual volume dispensed by the pipet ... 

Jars containing the same amount of hand wash solution as used to collect the entire hand wash from the test volunteer should be fortified. The samples are fortified with the appropriate amount of active ingredient solution using a 1-mL volumetric pipet, blowing out the remaining solution in the pipet. The solutions are capped, shaken, and placed immediately in a freezer or dry-ice cooler. 

Face wipe samples are treated similarly. The face wipe is placed in an appropriate jar and wet with the appropriate amount of wash solution. The sample is then spiked using a 1-mL volumetric pipet and immediately capped, processed, and frozen. 

Control urine should be collected from individuals who have no apparent past history of exposure to the active ingredient. This control urine must be stored frozen until used for field fortification purposes. The urine is then thawed, shaken well, and a certain amount should be aliquoted into a small jar/bottle to use for field fortification. The active ingredient is then added to the urine using a 1-mL volumetric pipet, the solution is shaken well, and the sample is immediately frozen. Occasionally, the fortified sample can be left at room temperature or at some lower temperature in a liquid state to simulate field storage during collection of the urine sample. After leaving the sample at such temperatures for the prescribed length of time, the sample is immediately stored frozen. 

Beakers 10 to 1000-ml. volumetric flasks 1-ml. volumetric pipet, serological pipet steam bath vacuum desiccator vacuum pump and water aspirator are also required. 

Procedure. Five aliquots of the triazole stock solution of 5, 10, 15, 20, and 25 ml. are introduced into 50-ml. volumetric flasks. Each aliquot is diluted to 50 ml. with hexane, making working standards equivalent to 10, 20, 30, 40, and 50 micrograms of triazole per ml., respectively. Using a volumetric pipet, 1 ml. of each working standard is... 

Graduated cylinders are not as precisely calibrated as burets or volumetric pipets. Briefly explain why it is acceptable to measure the K1 and HC1 solutions used in the titration with graduated cylinders rather than with pipets or burets. 

A student failed to allow the volumetric pipet to drain completely when transferring the diluted bleaching solution to the Erlenmeyer flask. 

If a student failed to drain completely the volumetric pipet when transferring the diluted bleach, this error would result in an incorrectly low percent of NaOCl. NaOCl is the active ingredient in bleach. If incorrect low amounts are transferred to the Erlenmeyer flask, then the NaOCl concentration is also incorrect. 

FIGURE 4.2 Drawings of the common glassware used in titrimetric analysis (not drawn to scale). Left, buret center, volumetric pipet right, volumetric flask. (From ChemClip Art 1000, a product of Molecular Arts Corporation, Anaheim, California. With permission.)... 

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... 

For precise work, volumetric pipets that are labeled class A have a certain time in seconds imprinted near the top (see Figure 4.10) this is the time that should be allowed to elapse from the time the finger is released until the pipet is completely drained. The reason for this is that the film of solution adhering to the inner walls will continue to slowly run down with time, and the length of time one waits to terminate the delivery thus becomes important. The intent with class A pipets, then, is to take this rundown time into account by terminating the delivery in the specified time. After this specified time has elapsed, the delivery is terminated. 

Prepare five identical dilutions of the stock solution prepared in step 1 by diluting 10 mL of the solution to 100 mL. Use a clean 10-mL volumetric pipet and a clean 100-mL volumetric flask, and make the measurement and transfer as carefully as possible (see Table 4.1). Label each as 2/1, 2/2, etc., to indicate that they are solutions 1 to 5 prepared in step 2. 

Define standard solution, volumetric flask, volumetric pipet, standardization, buret, stopcock, titration, titrant, substance titrated, equivalence point, indicator, end point, and 9automatic titrator. 

Which is more accurate, a Mohr pipet or a volumetric pipet Why ... 

Compare a volumetric pipet with a serological measuring pipet in terms of ... 

Using a volumetric pipet, add 50.00 mL of 0.2 MHC1 to each flask and dissolve the tablets. Using a graduated cylinder, add 50 mL of distilled water to each flask. Heat the flasks on a hot plate and boil the solutions gently for approximately 10 min. 

After the flasks have cooled, swirl the solutions and add four or five drops of bromcresol green or methyl red indicator mix. If the solution is green, all the base has not been neutralized. In this case, add 25.00 mL of 0.2 M HC1 with a volumetric pipet and boil again for 10 min. Repeat this process until the solution remains red. 

Prepare 100 mL of a 100 ppm Fe stock solution from the available 1000 ppm stock solution. Use a clean 100-mL volumetric flask and a clean volumetric pipet. Shake well. 

A volumetric pipet, because the diameter of the tube where the calibration fine is located is narrower. 

A 25-mL Class A volumetric pipet is certified by the manufacturer to deliver 25.00 0.03 mL. The volume delivered by a given pipet is reproducible, but can be anywhere in the range 24.97 to 25.03 mL. The difference between 25.00 mL and the actual volume delivered by a particular pipet is a systematic error. It is always the same, within a small random error. You could calibrate a pipet by weighing the water it delivers, as in Section 2-9. 

If you use an uncalibrated 25-mL Class A volumetric pipet four times to deliver a total of 100 mL, what is the uncertainty in 100 mL Because the uncertainty is a systematic error, the uncertainty in four pipet volumes is like the uncertainty in the mass of 4 moles of oxy-... 

An error of 1 0 mm was made in adjusting the meniscus (liquid level) to the mark in a 10 ml volumetric pipet The internal diameter of the pipet stem was... 

F Volumetric pipet courtesy of VWR Scientific, Division of Univar. G Mohr pipet courtesy of VWR Scientific, Division of Univar. 

Release liquid from the pipet until the bottom of the meniscus is directly on the fill line. Transfer the pipet to the inside of the second container and release the liquid. Hold the pipet vertically, allow the solution to drain until the flow stops, and then wait an additional 5 to 10 seconds. Touch the tip of the pipet to the inside of the container to release the last drop from the outside of the tip. Remove the pipet from the container. Some liquid may still remain in the tip. Most volumetric pipets are calibrated as TD (to deliver), which means the intended volume is transferred withoutfinal hlow-oul, i.e., the pipet delivers the correct volume. 

The use of a Mohr pipet is similar to that of a volumetric pipet. Draw the liquid into the pipet with a pipet filler to a level about 2 cm above the 0 mark. Lower the liquid level to the 0 mark. Remove the last drop from the tip by touching it to the inside of the glass container. Transfer the pipet to the receiving container and release the desired amount of solution. The solution should not be allowed to move below the last graduated mark on the pipet. Touch off the last drop. 

Pipettor pump courtesy of Cole-Parmer Instrument Co E Pasteur pipet courtesy of VWR Scientific, Division of Univar F Volumetric pipet courtesy of VWR Scientific, Division of Univar 6 Mohr pipet courtesy of VWR Scientific, Division of Univar H Serological pipet courtesy of VWR Scientific, Division of Univar... 

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