Flasks, marking

The checkers placed 250 ml. of dry xylene in a 500-ml. round-bottomed flask marked with a line corresponding to a volume of 424 ml. and with a gas inlet above the line. A cold finger containing a mixture of dry ice and methanol was attached to the flask, which was immersed in the same mixture. Gaseous boron trichloride (Matheson Co.) was passed in until the flask was filled to the 424-ml. line, and the cold solution was transferred to the dropping funnel. 

Carefully transfer ten 50-mL aliquots from the pipet to a dry 500-mL volumetric flask. Mark the location of the meniscus with a gummed label. Cover with a label varnish to ensure permanence. Dilution to the label permits the same pipet to deliver precisely a one-tenth aliquot of the solution in the flask. Note that recalibration is necessary if another pipet is used. 

Dilute to the mark with petroleum ether and thoroughly mix the contents of the flask. Mark this flask " Sample". 

An apparatus for reaction of solutions of alkali metals in NHg with solid materials (G. Brauer and V. Stein D.0]) is shown in Fig. 72. The alkali metal is sealed in a small ampoule which is provided with a small hook at one end. The seal point is broken off the ampoule is suspended by the hook from a thin wire and introduced into the apparatus. The ampoule contents are melted in a stream of Ng and flow to B. Then NHg is condensed in B. The solid is already in A, and both substances are combined by tipping the apparatus. After evaporation of the NHg the reaction product is transferred to analysis flasks, Mark capillaries, or to containers such as shown in Fig. 54a. From these it can be further transferred, as required. 

Weigh out accurately about 2-5 g. of pure powdered succinic acid, transfer to a 100 ml. graduated flask, dissolve in distilled water, make the solution up to the graduation mark and mix well. Now, by means of a pipette, transfer 25 ml. of the solution to a 150 ml. conical flask, add a drop of phenolphthalein solution and titrate with A/ 2 NaOH or KOH solution to obtain consistent results. 

Note, (i) In view of the large volume of. "l/.NaOH solution required in the above titrations, the contents of the flask A after hydrolysis niay alternatively be washed carefully into a 100 ml. graduated flask, and the solution made up to the mark and well mixed. 25 ml. of the-solution are then withdrawn with a pipette, and titrated with the A/.NaOH solution. The 100 ml. flask is then washed out repeatedly with distilled water, and used similarly for the contents of the flask B. 

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. 

Dissolve the sample in about 100 mL of H2O, and then dilute to the mark. Using a pipet, transfer a 25-mL aliquot of this solution to a 125-mL Erlenmeyer flask, and add 25-mL of H2O and 2 drops of bromocresol green indicator. Titrate the sample with 0.1 M HCl to the indicator s end point. 

In molecular weight determinations it is conventional to dissolve a measured mass of polymer m2 into a volumetric flask and dilute to the mark with an appropriate solvent. We shall use the symbol Cj to designate concentrations in mass per volume units. In practice, 100-ml volumetric flasks are often used, in which case C2 is expressed in grams per 100 ml or grams per deciliter. Even though these are not SI units, they are encountered often enough in the literature to be regarded as conventional solution units in polymer chemistry. 

The propyne (b.p. —23.2°) is precondensed to the mark in a volumetric flask cooled by acetone-dry ice. Evaporation of some propyne during addition will lead to a moderate molar excess of l-bromo-3-chloropropane, regarded as desirable in preventing formation of diyne product. 

Boil the tartaric acid and caustic soda solution for three hours in a round flask (I litre), or preferably in a tin bottle furnished with reflu. condenser. The use of a tin vessel obviates certain clitli-cultiesof filtration which the solution of the silica by the action of the alkali on the glass entails. The liquid, after boilinjg, is carefully neutralised with cone, hydrochloric acid (it is acl is-able to remove a little of the solution beforehand in case overshooting the mark) and an excess of calcium chloride solution is added to the hot liquid. The mixture is left overni hl. and the calcium salts filtered off at the pump, washed with water, and well pressed. 

The dislillale ia collected in a oOO c.c. Krkniueyar flask having a mark upon it 1c indicate the level of 2o0 c.c. Phenolpbthalein solution and a an tEcicnt excess of deci-normal sodium hydroxide solution ar,r lulded to the distillate and tho excess of alkali determined by lack-titralina. 

Ciamician and Silber have found that. light has a marked effect on methyl-heptenone. The ketone was kept in a glass flask, exposed to the light for five months, the flask being exhausted of air, which was replaced by oxygen. When the seal was broken, the contents of the flask were found to be at reduced pressure, and the oxygen was mainly converted into carbon dioxide. 

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