Weighing accurate

Na3S04 (P) 142.04 Weigh accurately 14.204 g, dried at 150°C, and dissolve in distilled water. Dilute to exactly 1 L. 

An alcohol-free solution of diazomethane in ether is prepared as in Chapter 17, Section III. This solution is approximately 0.5 M in diazomethane and may be standardized by titration as follows benzoic acid (0.6 g, approx. 0.005 mole) is weighed accurately into an Erlenmeyer flask and suspended in 5 ml of ether. The diazomethane solution (approx. 5 ml) is added from a buret with swirling, care being taken that an excess of unreacted benzoic acid remains (the yellow color of the diazomethane should be completely discharged). The excess benzoic acid is now titrated with standard 0.2 N sodium hydroxide solution, and the concentration of diazomethane is calculated. 

The most precise measurements of corrosion resistance require the use of specimens that can be weighed accurately after careful removal of corrosion products by the techniques described earlier. 

Procedure. To determine the purity of a sample of boric acid, weigh accurately about 0.8 g of the acid, transfer quantitatively to a 250 mL graduated flask and make up to the mark. Pipette 25 mL of the solution into a 250 mL conical flask, add an equal volume of distilled water, 2.5-3 g of mannitol or sorbitol, and titrate with standard 0.1 M sodium hydroxide solution using phenolphthalein as indicator. It is advisable to check whether any blank correction must be made dissolve a similar weight of mannitol (sorbitol) in 50 mL of distilled water, add phenolphthalein, and ascertain how much sodium hydroxide solution must be added to produce the characteristic end point colour. 

Procedure. Pipette 25.0 mL standard (0.05M) iodine solution into a 500 mL conical flask and add 5 mL 2M hydrochloric acid and 150 mL distilled water. Weigh accurately sufficient solid sulphite to react with about 20 mL 0.05M iodine solution and add this to the contents of the flask swirl the liquid until all the solid has dissolved and then titrate the excess iodine with standard (0.1M) sodium thiosulphate using starch indicator. If the sulphite is in solution, then a volume of this equivalent to about 20 mL of 0.05M iodine should be pipetted into the contents of the flask in place of the weighed amount of solid. 

Procedure. Prepare an approx. 0.02M standard solution of potassium bromate by weighing accurately about 1.65 g of the analytical grade reagent, dissolving it in water and making it up to 500 mL in a graduated flask (Note 2). 

Procedure. Dry some finely powdered pyrites at 100 °C for 1 hour. Place about 1 g of anhydrous sodium carbonate into the crucible, and weigh accurately into it 0.4-0.5 g of the pyrites. Add 5-6 g of sodium peroxide, and mix well with a... 

For initial practice in the method determine the manganese content of anhydrous manganese(II) sulphate. Heat manganese(II) sulphate crystals to 280 °C, allow to cool, grind to a fine powder, re-heat at 280 °C for 30 minutes, and allow to cool in a desiccator. Weigh accurately about 2.2 g of the anhydrous manganese(II) sulphate, dissolve it in water and make up to 250 mL in a graduated flask. 

Reagents. Copper ion solution, 0.04M. Wash analytical grade copper with petroleum spirit (b.p. 40-60 °C) to remove any surface grease and dry at 100 °C. Weigh accurately about 1.25 g of the pure copper, dissolve it in 5mL of concentrated nitric acid, and dilute to 1 L in a graduated flask. Titrate this... 

Approximately 10-g sample is weighed accurately by the Benchmate balance. 

The test consists of weight-loaded piston under the action of gravity forcing a heat-softened polymer through a rod die of specified dimensions [22], A small amount of a sample, typically about 4—5 gm, is packed into the barrel, avoiding air pockets, which is then pre-heated for a specified time for polyethylene this is 5 min at 190°C for PP this is 6 min at 230°C. After this, a weight, usually 2.16 kg, is loaded onto the top of the piston. Three samples are then cut from the extruded melt at constant time intervals, which are each then weighed accurately, and the... 

Weigh and finely powder not less than 30 tablets. Weigh accurately a portion of the powder, equivalent to about 700 mg of primaquine phosphate, and transfer to a... 

The compound must be weighed accurately and must not undergo composition change due to reaction with atmospheric components. 

Subtle differences in the instructions can make a big difference in the way that a task is carried out and can have a significant effect on events if the instructions are not followed correctly. This works both ways. Obviously, if you weigh something approximately when it should be weighed accurately then you run into problems, but on the other hand if you weigh accurately when an approximate result is appropriate, you end up wasting time and effort. 

Weigh and finely powder not less than 20 methimazole tablets. Weigh accurately a portion of the powder equivalent to about 120 mg of methimazole and place in 100 ml volumetric flask. Add about 80 ml of water, insert the stopper and shake by mechanical means or occasionally by hand during 30 minutes, dilute with water to volume and mix. Filter and transfer 50.0 ml of the filtrate to a 125 ml conical flask. Add from a burett3.5 ml of 0.1N NaOH, mix, and add with agitation about 7 ml of 0.1N AgN03. Add 1 ml of bromothymol blue T.S. and continue the titration with 0.1N NaOH until a permanent, blue green color is produced. Each ml of 0.1N NaOH is equivalent to 11.42 mg of C,H,N S. 

However, a gravimetric procedure might still be used if a chemical reaction is employed to convert the analyte to another chemical form that is both able to be separated cleanly and able to be weighed accurately. In the example of determining sodium sulfate in the presence of sodium chloride, one can dissolve the mixture in water and precipitate the sulfate with barium chloride to form barium sulfate. Sodium chloride would not react. 

The alternative to the above is using an accurately weighed solid material as the known standard. Such a material is called a primary standard. Thus, a primary standard is a material that can be weighed accurately either for the purpose of preparing a standard solution (which then does not have to be standardized) or for comparison to a solution with which it reacts for the purpose of standardizing that solution. For standardization with a primary standard, Equation (4.21) becomes... 

With a pair of forceps place the empty boat on the pan of the balance and carefully weigh accurately to 0-01 mg. Set the boat on a clean piece of paper, put in the substance, brush the outside clean with a fine hair brush, and determine the increase in weight with an accuracy of 0-01 mg. For C and H determinations weigh 26-30 mg. After weighing, set the boat again on the copper block and cover with a small glass dish. 

The apparatus for the determination of active hydrogen is shown in Fig. 45. The Lunge nitrometer a, of which the levelling bulb is not shown in the sketch, is filled with saturated brine. By means of the short calcium chloride tube 6, interposed between the reaction vessel and the nitrometer, the access of water vapour to that vessel is prevented. For the determination weigh accurately, according to... 

Standard Iron Solution Weigh accurately 0.1726 g of ferric ammonium sulphate and dissolve in 10 ml of 0.1 N sulphuric acid and sufficient water to produce 1 Litre. Each ml of this solution contains 0.02 mg ofFe. 

It is an usual practice that when a solid substance is to be assayed, an aliquot quantity of the same may be weighed accurately and dissolved in sufficient water so that the resulting solution should have more or less the same equivalent concentration as that of the acid used in the titration. Methyl orange (pH range = 3.0 to 4.4) is the indicator of choice for obvious reasons, as phenolphthalein and most other indicators are instantly affected by the carbonic acid (H2C03) generated in the reaction which ultimately cause a change in colour even before the reaction attains completion. 

Procedure Weigh accurately about 1 g, dissolve in 20 ml of water (DW) and titrate with 0.5 N sulphuric acid, using methyl orange solution as indicator. Each ml of 0.5 N sulphuric acid is equivalent to... 

Procedure Weigh accurately about 1.5 g of sodium hydroxide and dissolve in about 40 ml of carbon-dioxide free distilled water (i.e., boiled and cooled DW). Cool and titrate with 1 N sulphuric acid using phenolphthalein solution as indicator. When the pink colour of the solution is discharged record the volume of acid solution required. 

Procedure Weigh accurately about 0.25 g of busulphan, add 25 ml of DW and boil gently under a reflux condenser for 30 minutes. Wash the condenser with a small quantity of DW, cool and titrate with... 

Procedure Weigh accurately about 0.5 g of potassium hydrogen phthalate in a 100 ml conical flask. Add 25 ml of glacial acetic acid and attach a reflux condenser fitted with a silica-gel drying tube. Warm until... 

Procedure Weigh accurately about 0.2 g and dissolve in 15 ml of anhydrous formic acid, 30 ml of glacial acetic acid and 30 ml of dioxane. Add 0.1 ml of crystal violet solution and titrate with 0.1 N perchloric acid. Perform a blank determination and make any necessary correction. Each ml of 0.1 N perchloric acid is equivalent to 0.02112 g of C10H13NO4. 

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