Volumetric procedures

Classical wet chemical methods and instmmental techniques are used for the analysis of soluble sibcates (91). Sibca is deterrnined by gravimetric techniques or by the fluorosibcate volumetric procedure. 

Zirconium is often deterniined gravimetrically. The most common procedure utilizes mandelic acid (81) which is fairly specific for zirconium plus hafnium. Other precipitants, including nine inorganic and 42 organic reagents, are Hsted in Reference 82. Volumetric procedures for zirconium, which also include hafnium as zirconium, are limited to either EDTA titrations (83) or indirect procedures (84). X-ray fluorescence spectroscopy gives quantitative results for zirconium, without including hafnium, for concentrations from 0.1 to 50% (85). Atomic absorption determines zirconium in aluminum in the presence of hafnium at concentrations of 0.1—3% (86). 

Coulometric methods are as accurate and precise as conventional gravimetric and volumetric procedures and, in addition, are readily automated. In contrast to gravimetric methods, coulometric procedures are usually rapid, and do not require that the product of the electrochemical reaction be a weighable solid. The methods are moderately sensitive, and offer a reasonably selective means for separating and determining a number of ions. 

The sample is acidified with sulfuric acid. The bromide content is then determined by the volumetric procedure described by Kolthoff and Yutzy [21 ]. In this procedure the buffered sample is treated with excess sodium hypochlorite to oxidise bromide to bromate. Excess hypochlorite is then destroyed by addition of sodium formate. Acidification of the test solution with sulfuric acid followed by addition of excess potassium iodide liberates an amount of iodine equivalent to the bromate (i.e., the original bromide) content of the sample. The liberated iodine is titrated with standard sodium thiosulfate. 

Solutions of known ionic strength are now available commercially, as are tablets of inert electrolyte, where the latter are dissolved in a known volume of water to produce a solution of predetermined I - this is merely a volumetric procedure. Such tablets are much like buffer tablets, and are called ionic strength adjusters. 

A. Zinc Reduction-Volumetric Procedure (Ref l6a, Method 203-5)- This method is used for determining the DBuPh and DEtPh content of proplnts that do not contain interfering esters such as other phthalates, dimethyl sebacate, triacetin, or sucrose octa-acetate... 

At higher levels, cadmium may be estimated gravimetrically following precipitation with sulfide (20), P-naphthoquinoline (21), or after plating from a cyanide-containing solution onto a stationary platinum cathode. Volumetric procedures rely on preliminary precipitation of the sulfide that is purified and then dissolved in acid whereupon the liberated H2S may be titrated with iodine. An alternative, should zinc be a likely contaminant, is to precipitate with diethyldithiocarbamate and then to redissolve in acid and titrate with sodium ethylenetriaminetetraacetate (HDTA) using Eriochrome Black T as indicator (22). 

Procedures in which we measure the volume of reagent needed to react with analyte are called volumetric analysis. In this chapter, we discuss principles that apply to all volumetric procedures and then focus on precipitation titrations. We also introduce spectrophotometric titrations, which are especially useful in biochemistry. 

Here are some examples to illustrate stoichiometry calculations in volumetric analysis. The key step is to relate moles of titrant to moles of analyte. We also introduce the Kjeldahl titration as a representative volumetric procedure. 

The Karl Fischer titration,30 which measures traces of water in transformer oil, solvents, foods, polymers, and other substances, is performed half a million times each day.31 The titration is usually performed by delivering titrant from an automated buret or by coulometric generation of titrant. The volumetric procedure tends to be appropriate for larger amounts of water (but can go as low as 1 mg H20) and the coulometric procedure tends to be appropriate for smaller amounts of water. 

Centralite 3, Analytical Procedures. Accdg to Kast-Metz(1944), 167, color reactions of Centr 3 are identical with those described under Centr 1. Some gravimetric and volumetric procedures described in Kast-Metz(l944), 292-3 are applicable to detn of Centr 3 in smokeless proplnts. No other info is at out disposal Centralite 3, Nitro Derivatives. No info at our disposal... 

The molalities m (concentration in moles per kilogram of solvent) that are needed for the calculations can be obtained from the molarities M (concentration in moles per liter of solution) obtained from the volumetric procedures by using the equation... 

The constituents determined in an analytical procedure can cover a huge range in concentration. In some cases, analytical methods are used to determine major constituents. These constituents are present in the relative weight range of 1% to 100%. Many of the gravimetric and some of the volumetric procedures discussed in Part III are examples of major constituent determinations. As shown in Figure 8-2, species present in the range of 0.01% to 1% are usually termed minor constituents, whereas those present in amounts between 100 ppm (0.01%) and 1 ppb are termed trace constituents. Components present in amounts less than 1 ppb are usually considered to be ultratrace constituents. 

Coulometric titration offers several significant advantages over a conventional volumetric procedure. Principal among these is the elimination of the problems asso-... 

Portable Orsat is a separation technique that involves the selective absorption and quantitative measurement of one gas from a mixture of gases. Such a mixture might be the exhaust gas from an engine, the gas in a mine shaft, the gas in a sewer, or the gas in a silo. This is a true volumetric procedure. All quantitative values depend on volumes measured. Few, if any, of you have ever really handled a gas. You may have prepared Hj, COj, or Oj as a freshman chemistry laboratory experiment, but you have never had to collect and separate a mixture of gases. This chapter will show you several reagents that are used to absorb various gases, how to collect a gas sample, and how to separate it into several of its components. 

A coulometric titration, like a more conventional volumetric procedure, requires some means of detecting the point of chemical equivalence. Most of the end-point detection methods applicable to volumetric analysis are equally saiisfactory here. Visual observations of color changes of indicators, as well as poicn-tionieiric, amperometric, and photometric measurements have all been used successfully. 

Fellow chemists will undoubtedly notice that this is an absurdly low precision for a volumetric procedure. We are doing some exaggeration for didactical purposes. 

Total phosphorus (as P2O6). A 10-ml. aliquot is diluted to approximately 100 ml., and 20 ml. of concentrated nitric acid is added. The solution is boiled for 20 to 30 minutes to hydrolyze the poly- and metaphosphates to orthophosphate. After cooling, the solution is neutralized to methyl orange with ammonium hydroxide and is again cooled to room temperature. Phosphate is precipitated as ammonium 12-molybdophosphate, filtered, washed, and titrated by the volumetric procedure recommended for fertilizers. ... 

Today, volumetric determination of dissolved substances in water can be automated. With appropriate equipment, it is possible not only to direct the reaction quantitatively, but also to evaluate the endpoint of the reaction electrometrically and print it out, for example, or produce a titration diagram. The experience of the authors has shown the volumetric procedures described in Chapters 3 and 4 to be of particular value in practical water analysis in the laboratory. 

I n volumetric analysis, the volume of a known reagent required for complete reaction with analyte by a known reaction is measured. From this volume and the stoichiometry of the reaction, we calculate how much analyte is in an unknown substance. In this chapter we discuss general principles that apply to any volumetric procedure, and then we illustrate some analyses based on precipitation reactions. Along the way, we introduce the solubility product as a means of understanding precipitation reactions. 

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