Volume measurement graduated pipettes

Procedure. Weigh out accurately about 4 g of the pure organic acid, dissolve it in the minimum volume of water (Note 1), or 1 1 (v/v)ethanol/water mixture, and transfer the solution to a 250 mL graduated flask. Ensure the solution is homogeneous and make up to the required volume. Use a pipette to measure out accurately a 25 mL aliquot and transfer to a 250 mL conical flask. Using two drops of phenolphthalein solution as indicator, titrate with standard 0.2M (approx.) sodium hydroxide solution (Note 2) until the colourless solution becomes faintly pink. Repeat with further 25 mL volumes of the acid solution until two results in agreement are obtained. 

Volumetric analysis essentially comprises of the most precise and accurate measurement of interacting solutions or reagents. It makes use of a number of graduated apparatus, such as graduated (volumetric) flasks, burettes, pipettes and measuring cylinder of different capacities (volumes). 

Graduated Pipettes They have graduated stems and are used to deliver different small volumes as needed. However, they are not normally used for measuring very exact volumes of liquids. 

Pipettes are used for the exact measurement of a definite volume of a liquid. They are narrow cylindrical glass tubes with still narrower top and bottom ends (Fig. 4a). The upper part of an ungraduated pipette has a mark showing up to what level it must be filled to obtain the volume indicated on it. Pipettes with a volume of 10 or 20 ml are used the most. Graduated pipettes are also used (Fig. 45). 

Put the lid in place and switch on the apparatus. Carefully add 0.1 N sodium hydroxide with stirring to adjust to pH 9.2. Using a rapid-flow graduated pipette, transfer about 05 mL of the previously homogenized reference suspension, start the chronometer, and add continuously 0.1 N sodium hydroxide to maintain the pH at 9.0. After exactly 1 min, note the volume of 0.1 N sodium hydroxide used. Carry out the measurement a further four limes. Discoid the first reading and determine the average of the four others (Si). Make two further determinations (S2 and Sa). Calculate ihe average of the values, Si, Si, and S3. 

Use a 1-mL pipette graduated in 0.01-mL increments to measure out 0.010 mol of solute, and use a 2-mL graduated pipette to then add the correct amount (0.040 mol) of solvent. You may neglect the presence of the 5 percent TMS when determining the necessary volumes of solvent. Warning All work with TMS should be carried out in a hood. All containers or samples containing TMS should be tightly sealed and stored at low temperatures because of its volatility. 

Modem Erlenmeyer flasks and beakers have approximate volume calibrations fused into the glass, but these are very approximate. Somewhat more accurate volumetric measurements are made in the 10-mL graduated cylinders. For volumes less than about 4 mL, use a graduated pipette. Never apply suction to a pipette by mouth. The pipette can be fitted with a small rubber bulb. A Pasteur pipette can be converted into a calibrated pipette with the addition of a plastic syringe body [see Fig. 11(d)] or you can calibrate it at 0.5, 1.0, and 1.5 ml and put three file scratches on the tube this eliminates the need to use a syringe with this Pasteur pipette in the future. Also see the Pasteur pipette calibration marks in the back of this book. You should find among your equipment a 1-mL pipette, calibrated in hundredths of a milliliter [Fig. 11(a)]. Determine whether it is designed to... 

Volume measuring means the exact determination of a defined volume of a liquid (or of a powder mixture in the case of preparing capsules). Devices for measuring of volumes for pharmacy preparations include graduated pipettes (traditional or automatic), syringes and graduated cylinders. Beakers, Erlenmeyer flasks and medicine bottles are not fit for volume measurement, even if they are... 

The imprecision of the read-out can be made as small as possible by choosing a graduated pipette, syringe or measuring cylinder with a nominal capacity as near to the volume to be measured as possible. For example a volume of 0.5 mL should be measured by a 0.5 mL automatic pipette or with a 1.0 mL traditional graduated pipette. A volume of 21 mL should preferably be measured with a 25 mL graduated pipette or a measuring cylinder of a nominal volume of 25 mL. 

Prepare four standard solutions consisting of 2.00 ml of the dilute nitrite solution (measured with a 2.00-ml graduated pipette) made to a volume of 50 ml in a graduated flask or 50-ml measuring cylinder. Transfer the solutions to four dry 125-ml Erlenmeyer flasks and place 50 ml of distilled water in two more flasks to act as blanks. Carry out the nitrite determination as described in Section F, paragraphs 2-3. 

Figure 1.15 a A funnel is used to fill the burette with hydrochloric acid, b A graduated pipette is used to measure 25.0cm of sodium hydroxide solution into a conical flask, c An indicator called litmusisadded to the sodium hydroxide solution, which turns blue, d 12.5 cm of hydrochloric acid from the burette have been added to the 25.0 cm of alkali in the conical flask. The litmus has gone red, showing that this volume of acid was just enough to neutralise the alkali. 

Figure P2.3 Volumetric and graduated pipettes are used to transfer accurate volumes of liquid. Volumetric pipettes give greater accuracy than graduated pipettes, due to the single line to measure to on the thin section above the bulge.

There are four categories of containers used to measure volume volumetric flasks, graduated cylinders, burettes, and pipettes. Of the four, volumetric flasks are used exclusively to measure how much has been put into them. This use is known as to contain. Graduated cylinders and a few pipettes are used to measure how much has been put into them as well as how much they can dispense. The latter measurement is known as to deliver. Burettes and most pipettes are used solely to deliver. 

An important general rule in the quantitative handling of liquids is that the graduated vessel or pipette should be of a size appropriate to the volume being measured it is certainly not sensible to measure out a few ml of liquid in a 100 ml measuring cylinder, nor a few pi with an adjustable pipette that holds 100 pi. 

Measuring Liquids and Gases. — Liquids are measured in graduated cylinders, or graduates, tubes, burettes, and pipettes. Vessels of various capacities are used, depending upon the volume of liquid to be measured. A... 

Weigh out 0.6 mole of sodium hydroxide, dissolve in about 60 ml of distilled water, and make the volume of the solution up to 100 ml in graduated cylinder. At the same time, procure some 60 per cent perchloric acid and determine the volume of this acid that reacts with imit volume of sodium hydroxide by taking a small volume of sodium hydroxide (say 2 ml measured by a pipette) and making up to 100 ml in a volumetric flask transfer to a clean, diy flask, rinse the volumetric flask and pipette, and dilute the perchloric acid in exactly the same manner. Fill a burette with the diluted perchloric acid and titrate 25-ml portions of the diluted sodium hydroxide. Since both the acid and the base are strong, almost any indicator will be satisfactory. When you have two titrations that agree to about 0.5 per cent, pour the remaining 98 ml of 6-molar sodium hydroxide into a... 

To standardize the mercuric nitrate, pipette 10 ml of O.lN potassium chloride into a 250-ml Erlenmeyer flask then add 40 ml of water (measured with a graduate) and 3 drops of 10 per cent sodium nitroprusside. Titrate with mercuric nitrate, shaking well between additions as the end point is neared. The end point is marked by a permanent white turbidity and is quite sharp. When the mercuric nitrate has been standardized, titrate the hexamminecobaltic chloride solution by the same procedure, taking care to have the volume of solution in the titration flask the same as in the standardization. The end point arrives somewhat early because of the reaction HgCh + Hg++—> 2HgCl+ but by performing the standardization and titration under similar conditions, with the final mercuric chloride concentrations almost the same, this error, which is small in any case, becomes quite negligible. 

Suppose, for example, that you want to determine the molar concentration of an HCl solution. Rrst, you place a known volume (say, 25.00 milliliters measured accurately with a pipette) in an Erlenmeyer flask (that s just a flat-bottomed, conical-shaped flask) and add a couple drops of phenolphthalein solution. Because you re adding the indicator to an acidic solution, the solution in the flask remains clear and colorless. You then add small amounts of a standardized sodium hydroxide solution of known molarity (for example, 0.100 kQ with a buret. (A baret is a graduated glass tube with a small opening and a stopcock, which helps you measure precise volumes of solution.)... 

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