Volumetric standards

KBr03- Formed from Brj and hot aqueous KOH. Decomposes to KBr and Oj on heating. Used as a volumetric standard. See brom-... 

Adipic acid [124-04-9] M 146.1, m 154 , pK 4.44, pK 5.45. For use as a volumetric standard, adipic acid was crystd once from hot water with the addition of a little animal charcoal, dried at 120 for 2h, then recrystd from acetone and again dried at 120 for 2h. Other purification procedures include crystn from ethyl acetate and from acetone/petroleum ether, fusion followed by filtration and crystn from the melt, and preliminary distn under vac. 

Benzoic acid [65-85-0] M 122.1, m 122.6-123.1, pK 4.12. For use as a volumetric standard, analytical reagent grade benzoic acid should be carefully fused to ca 130 (to dry it) in a platinum crucible, and then powdered in an agate mortar. Benzoic acid has been crystd from boiling water (charcoal), aq acetic acid, glacial acetic acid, C6H6, aq EtOH, pet ether (b 60-80 ), and from EtOH soln by adding water. It is readily purified by fractional crystn from its melt and by sublimation in a vacuum at 80. ... 

Sodium oxalate [62-76-0] M 134.0, m 250-270 (dec), d 2.34. Crystd from hot water (16mL/g) by cooling to 0°. Before use as a volumetric standard, analytical grade quality sodium oxalate should be dried for 2h at 120° and allowed to cool in a desiccator. 

Sodium carbonate [497-19-8] M 106.0. Crystd from water as the decahydrate which was redissolved in water to give a near-saturated soln. By bubbling CO2, NaHCO3 was ppted. It was filtered, washed and ignited for 2h at 280° [MacLaren and Swinehart JACS 73 1822 7957]. Before being used as a volumetric standard, analytical grade material should be dried by heating at 260-270° for 0.5h and allowed to cool in a desiccator. For prepcU ation of primary standard sodium carbonate, see PAC 25 459 1969. 

Ceric ammonium nitrate, the well-known volumetric standard oxidant, is formulated (NH4)2[Ce(N03)6] with 12-coordinated Ce4+ ions (each N03 ion being bidentate) in approximately Td symmetry. The Ce—O distances are in the range 2.488-2.530 A. The ligand bite is only 50.6-50.9° and the other O—Ce—O angles are 65.0-69.90.692 The carbonato complexes Na6[Ce(C03)5]-12H20 and [C(NH2)3]6[Ce(C03)5]-4H20 each show cerium ten-coordinated to five bidentate carbonate ions with Ce—O = 2.379-2.504 A in the first complex and 2.388-2.488 A in the second. The coordination polyhedra are irregular.693,694... 

Oxidation states higher than + 3 are exhibited by Ce, Pr, and Tb, but only Ce4+ is stable (kinetically) in water. It is a very strong oxidizing agent in aqueous solution ( ° = 1.74 V) and is used as a volumetric standard in redox titrations. Some of its salts [e.g., cerium(IV) ammonium nitrate, cerium(IV) sulfate] find application in... 

Advantages of volumetric standard solutions Solution stoichiometry... 

N and 0.05 N HC1 solutions were made by diluting volumetric standard 2 N HC1 with nanopure water. 

This salt is soluble in H,0, and exists iu the Lig, hydrargyri nUratis U. S,), Liq. hydrargyri nUtaiis acid us Br,) in the volumetric standard solution used in Liebig s process for urea and probably in citrine ointment 1= Ung. hydrar. nUratis (C S, Br,),... 

Reagent-grade chemicals are almost always used in analyses. Primary standards are used for preparing volumetric standard solutions. 

When an analytical standard or unknown sample is injected into a measuring instrument it is almost always in solution in some suitable solvent, so the question of measurement of liquid volume becomes an important consideration. Moreover, the analytical standard will be weighed when a series of calibration solutions is made however, frequently in practice the solvent will not be weighed (the best practice), but will be added to make the solution volume up to some pre-determined value using a volumetric standard flask. The volume concentration of the solution is thereby established, and the volume of solution delivered by a standardized pipet, loop injector or similar device determines the amount of analyte injected. 

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