Pipet graduated

Microscale student experiments reduce costs by decreasing consumption of reagents and generation of waste. An inexpensive student buret can be constructed from a 2-mL pipet graduated in 0.01-mL intervals.15 Volume can be read to 0.001 mL and titrations can be carried out with a precision of 1%. 

Volume Cubic meter (m3) Liter (L) Pipet, graduated cylinder,... 

Analytical chemists use a variety of glassware to measure volume, several examples of which are shown in Figure 2.4. The type of glassware used depends on how exact the volume needs to be. Beakers, dropping pipets, and graduated cylinders are used to measure volumes approximately, typically with errors of several percent. 

Preparing a solution of known concentration is perhaps the most common activity in any analytical lab. The method for measuring out the solute and solvent depend on the desired concentration units, and how exact the solution s concentration needs to be known. Pipets and volumetric flasks are used when a solution s concentration must be exact graduated cylinders, beakers, and reagent bottles suffice when concentrations need only be approximate. Two methods for preparing solutions are described in this section. 

A standard solution of Mn + was prepared by dissolving 0.250 g of Mn in 10 ml of concentrated HNO3 (measured with a graduated cylinder). The resulting solution was quantitatively transferred to a 100-mL volumetric flask and diluted to volume with distilled water. A 10-mL aliquot of the solution was pipeted into a 500-mL volumetric flask and diluted to volume, (a) Express the concentration of Mn in parts per million, and estimate uncertainty by a propagation of uncertainty calculation, (b) Would the uncertainty in the solution s concentration be improved... 

Voll-mundigkeit, /. (of liquors) body, palate fullness, -pipette, /. a pipet(te) delivering a single definite amount, without a graduated scale transfer pipet. Cf. Messpipette. 

The device most commonly used to measure volume in general chemistry is the graduated cylinder. A pipet or buret (Figure 1.8) is used when greater accuracy is required. A pipet is calibrated to deliver a fixed volume of liquid—for example, 25.00 mL—when filled to the mark and allowed to drain. Variable volumes can be delivered accurately by a buret, perhaps to 0.01 mL. 

Prepare a calcium stock solution (1000 mg L "1) by dissolving 2.497 g of dried calcium carbonate in a minimum volume of 1M hydrochloric acid about 50 mL will be required. When dissolution is complete, transfer the solution to a 1 L graduated flask and make up to the mark with de-ionised water. An intermediate calcium stock solution is prepared by pipetting 50 cm of the stock solution into a 1 L flask and making up to the mark with de-ionised water. 

Discard the Dump phase. Collect the Collect fraction in a 150-mL long-necked round-bottom flask or in a 250-mL pear-shaped flask. Concentrate the fraction to ca 1 mL in a rotary evaporator (rotate slowly, immerse the flask only slightly in the water-bath). Pipet the concentrated solution quantitatively into a ground stoppered graduated test-tube, rinse the flask with ethyl acetate and dilute the solution to 5.0 mL (Vge) with ethyl acetate. 

Cleanup of sample extract. Pipet 2.5 mL of the solution derived from Module GPC into a long-necked round-bottom flask or a pear-shaped flask and add 10 mL of isooctane. By rotating the flask slowly, carefully evaporate the solution to ca 1 mL in a rotary evaporator (water-bath temperature set at 30 0 °C). If an odor of ethyl acetate is still present, add isooctane again and repeat the evaporation. Repeat, if necessary, until no odor of ethyl acetate is present the ethyl acetate must be completely removed. Allow the solution to drain to the upper surface of the column packing and then place a graduated test-tube under the column. 

If the detectability of an analyte in a final eluate volume of 10 mL is not sufficient for the GC determination, then pipet an aliquot (Vi) of the eluate Vce into a 25-mL pear-shaped flask and concentrate the aliquot to ca 0.5 mL in a rotary evaporator (water-bath temperature 30 0 °C). By rinsing the flask, transfer the concentrated solution quantitatively into a graduated test-tube and dilute the sample to a suitable volume ( 2). Without this concentration step, volumes V and V2 need not be considered for the equation given below. 

Other apparatus includes a Waring Blendor, 1-quart mixing cup 24 or more 125-ml. Erlenmeyer flasks two 10-ml. graduated cylinders a 50-ml. glass-stoppered volumetric flask and 10-ml. volumetric and 5-ml. serological-type pipets. 

Commercial absolute ethanol (48 ml.) is pipetted into a 1-1. graduated cylinder and diluted with 800 ml. of ethyl acetate ( Eastman grade ). 

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. 

Common containers for liquid measurements include cylindrical and conical graduates for quantities of 500 mL or less, pipets for quantities of one mL or less, and a medicinal dropper for still smaller quantities. The calibration and use of medicinal droppers is explained in Chapter 2. 

As with the weighing of solids on a prescription balance, there are limitations to liquid measuring devices as well. For example, assume that only one pipet having graduations from one to ten milliliters is available, and it is desired to measure one fluid ounce. In such a case, one ounce can be measured by measuring 10 mL three times. Measurement of volumes less than that of the... 

A prescription requires 0.015 mL of a drug concentrate. Using a pipet with markings from one to ten in units of 1 mL and a 100-mL graduated cylinder, explain how you would obtain the required quantity of drug concentrate Use water as a diluent. 

Explain how one can obtain 2 minims of a liquid concentrate using a 5-mL pipet with graduations from 1-5 mL in units of 0.5 mL, and a 100-mL measuring cylinder. Use water as a diluent. 

FIGURE4.il The tips of two styles of measuring pipets. The Mohr pipet is shown on the left, and the serological pipet on the right. The graduation lines on the Mohr pipet stop short of the tip, but on the serological pipet, pass through the tip. 

Repeat step 2, but use a clean class A 10-mL graduated cylinder instead of the 10-mL volumetric pipet to measure the 10 mL of stock solution. Again, make each measurement and transfer as carefully as possible. Label each as 3/1, 3/2, etc., to indicate that they are solutions 1 to 5 prepared in step 3. 

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