PRACTICAL GRAVIMETRIC ANALYSIS

For all gravimetric determinations described in this chapter, the phrase Allow to cool in a desiccator should be interpreted as cooling the crucible, etc., provided with a well-fitting cover in a desiccator. The crucible, etc, should be weighed as soon as it has acquired the laboratory temperature (for a detailed discussion, see Section 3,22). 

14 DETERMINATION OF ALUMINIUM AS THE 8-HYDROXYQUINOLATE, AI(C,H60N)3 WITH PRECIPITATION FROM HOMOGENEOUS SOLUTION 

Discussion. Some of the details of this method have already been given in Section 11.11(C), This procedure separates aluminium from beryllium, the alkaline earths, magnesium, and phosphate. For the gravimetric determination a 2 per cent or 5 per cent solution of oxine in 2M acetic add may be used 1 mL of the latter solution is suffident to predpitate 3 mg of aluminium. For practice in this determination, use about 0.40 g, accurately weighed, of aluminium ammonium sulphate. Dissolve it in 100 mL of water, heat to 70-80 °C, add the appropriate volume of the oxine reagent, and (if a precipitate has not already formed) slowly introduce 2M ammonium acetate solution until a precipitate just appears, heat to boiling, and then add 25 mL of 2M ammonium acetate solution dropwise and with constant stirring (to ensure complete predpitation). 

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From the discussion presented of reactions in solids, it should be apparent that it is not practical in most cases to determine the concentration of some species during a kinetic study. In fact, it may be necessary to perform the analysis in a continuous way as the sample reacts with no separation necessary or even possible. Experimental methods that allow measurement of the progress of the reaction, especially as the temperature is increased, are particularly valuable. Two such techniques are thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These techniques have become widely used to characterize solids, determine thermal stability, study phase changes, and so forth. Because they are so versatile in studies on solids, these techniques will be described briefly. 

Experiment 4 Practice of Gravimetric Analysis Using Physical Separation Methods... 

Thermoanalytical methods essentially encompass such techniques that are based entirely on the concept of heating a sample followed by well-defned modified procedures, such as gravimetric analysis, differential analysis and titrimetric analysis. In usual practice, data are generated as a result of continuously recorded curves that may be considered as thermal spectra . These thermal spectra also termed as thermograms, often characterize a single or multicomponent system in terms of ... 

If there is introduced into the solution from some other source an ion that is in common with an ion of the insoluble solid, the chemical equilibrium is shifted to the left, and the solubility of that solid will be greatly decreased from what it is in pure water. This is called the 11 common-ion effect." This effect is important in gravimetric analysis, where one wishes to precipitate essentially all of the ion being analyzed for, by adding an excess of the "common-ion" precipitating reagent. There is a practical limit to the excess, however, which involves such factors as purity of precipitate and possibility of complex formation. You can calculate the solubility under a variety of conditions, as illustrated in the following problem. 

The practical work involved both volumetric and gravimetric analysis, as an anonymous author complained ... 

Chemistry Video Consortium, Practical Laboratory Chemistry, Educational Media Film and Video Ltd, Harrow, Essex, UK - Inorganic analysis (gravimetric analysis). 

IGA isothermal gravimetric analysis IPTS international practical temperature scale... 

Historically, our knowledge of the chemical composition of compounds and their formulas came from practical work on elemental analysis. This analysis was remarkable as it was carried out at a time when nothing was known about the structure of the atom or chemical bonding. The work has been termed gravimetric analysis and the progression to modern techniques illustrates how technical development builds on and expands scientific horizons. Subsequendy, more sophisticated methods have been added to the armoury of techniques by which we can determine not just the composition of compounds, but also their structures. 

Gravimetric and volumetric methods are practicable for the quantitative determination of the a-sulfo fatty acid esters. Using gravimetric methods the surfactant is precipitated with p-toluidine or barium chloride [105]. The volumetric determination method is two-phase titration. In this technique different titrants and indicators are used. For the analysis of a-sulfo fatty acid esters the quaternary ammonium surfactant hyamine 1622 (p,f-octylphenoxyethyldimethyl-ammonium chloride) is used as the titrant [106]. The indicator depends on the pH value of the titration solution. Titration with a phenol red indicator is carried out at a pH of 9, methylene blue is used in acid medium [106], and a mixed indicator of a cationic (dimidium bromide) and an anionic (disulfine blue VN150) dye can be used in an acid and basic medium [105]. 

Gravimetric methods provide precise and accurate results and have jpund a wide utility in chemical analysis for many years. They are best suited to the determination of major constituents in samples because of the practical limitations in accurately weighing quantities of less than 0.1 g. The analysis... 

The RFS technique is used as a comparative method due to the unavailability of oil standards with known gravimetric concentration of particles for each element measured by the spectrometer. In practice, a used oil sample is first analyzed using the standard RDE technique, which provides an analysis of dissolved and small wear particles. A second analysis of the same sample using the RFS technique detects large particles. The two analyses provide an indication of the wear particle size distribution in the sample. A sudden presence of large wear particles will not be seen by conventional analysis alone. Their presence, however, will be readily evident throu the RFS analysis. 

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