Silica titration determination

In a commercial sample of silicate, Na O (total alkali) and SiO (silica) are determined. 5 g of sodium silicate is dissolved in 100 ml water. 10 ml of this solution is titrated against 0.5 N H SO using Methyle Orange as an indicator. 

Silica sol standards are required for calibrating CZE retention. Figure 15 shows the correlation of CZE retention time with the surface area of several silica sols determined by a titration method (35). In this case, the silica sol diameter is directly related to the surface area by the expression... 

In Unger and Fischer s study of the effect of mercury intrusion on structure, three samples of porous silica were specially prepared from spherical particles 100-200 pm in diameter so as to provide a wide range of porosity (Table 3.16). The initial pore volume n (EtOH) was determined by ethanol titration (see next paragraph). The pore volume u (Hg, i) obtained from the first penetration of mercury agreed moderately well with u fEtOH),... 

Values of pore volume of samples of porous silica, determined by ethanol titration (v (EtOH)) and by mercury porosimetry (v (Hg, i) and v (Hg, ii)) ... 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

Into a suspension of 8 g of sodium acetate m 400 mL of a solution of 1 part acetic acid and 10 parts fluorotnchloromethane is passed at -75 C a stream of fluonne diluted to 10% with nitrogen The reacuon is stirred with a Vibromixer A solution of 4-methylacetanilide (20 mmol) in a mixture of dichloromethane and fluorotnchloromethane cooled to -75 °C i s added to 20 mmol of acetyl hypofluonte as determined by titration with potassium iodide After 5 min the mixture is poured into water, and the orgamc layer is washed with sodium bicarbonate soluaon and dried over anhydrous magnesium sulfate After concentrauon and column chromatography over silica gel and elution with chloroform, 2-fluoro-4-methylacetanilide IS obtained m 85% yield... 

A Welsbach T-816 Ozonator purchased from the Welsbach Corporation, Philadelphia, Pennsylvania, was used. The oxygen stream was dried by passage through dry silica gel and molecular sieves and then introduced into the ozonator with the operating voltage set at 115 V., the gas pressure at 8 p.s.i.g., and the gas flow rate at 1 1. per minute. The resulting ozone flow rate was 0.00245 mole per minute, as determined by titration of a potassium iodide trap. ... 

Apparatus and Procedure. The apparatus and procedure were identical to those outlined in ref. Surface composition measurements were based on an O2-CO titration technique described by Miura and Gonzalez (5-6). The ratio of surface metal/02/CO was 1/1/T on Ru-sllica, 1/0.5/1.75 on Rh-sllica, 1/0.5/2.0 on Pt-silica and 1/0.5/1.6 on Ir-silica. These titration ratios were found to be independent of surface composition. Surface compositions determined by the O2-CO titration method have been verified using a variety of experimental techniques (2,5-6). 

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

The bomb method for sulfur determination (ASTM D129) uses sample combustion in oxygen and conversion of the sulfur to barium sulfate, which is determined by mass. This method is suitable for samples containing 0.1 to 5.0% w/w sulfur and can be used for most low-volatility petroleum products. Elements that produce residues insoluble in hydrochloric acid interfere with this method this includes aluminum, calcium, iron, lead, and silicon, plus minerals such as asbestos, mica, and silica, and an alternative method (ASTM D1552) is preferred. This method describes three procedures the sample is first pyrolyzed in either an induction furnace or a resistance furnace the sulfur is then converted to sulfur dioxide, and the sulfur dioxide is either titrated with potassium iodate-starch reagent or is analyzed by infrared spectroscopy. This method is generally suitable for samples containing from 0.06 to 8.0% w/w sulfur that distill at temperatures above 177°C (351°F). 

A determination of the surface hydroxyl groups was made by Noll et al. (183). The total water content was determined by heating to 1100°. The content ofmolecular water was titrated by the Karl Fischer method. Silanol groups react with this reagent only very slowly. Good agreement was observed with silanol contents determined independently by other methods. With silica gel, 5.2 silanol groups were found per 100 A. ... 

Generation of acidity in silica gel by ionizing radiation was reported by Barter and Wagner (274). p-Dimethylaminoazobenzene was adsorbed out of anhydrous solution in CCI4 in the red, acid form. About 3 /aeq/gm of acid sites were generated by a dose of 3 10 rad, as determined by titration with butylamine. 

Figure 8 shows a separation of condensed aromatic hydrocarbons in which the water content of n-heptane used as the eluent was controlled by MCS. The water concentrations as determined by Karl-Fischer titration are also included for comparison. If all variables such as the water content of the silica in the MCS, the temperature of both MCS, and the chromatographic column are kept constant, the reproducibility of the k values is 2.5%. 

A Perkin-Elmer Model 21 infrared spectrophotometer was used to detect and to estimate the hydroxylic and carbonyl functions in the oxidized product mixtures. The organic hydroperoxide and peroxide functional groups in the product mixtures were determined by an iodine liberation and titration procedure (11). In order to get reproducible results, it is necessary to pretreat the olefins with about 10 weight % activated silica or alumina for several hours with agitation to remove adventitious peroxides and impurities. Sodium bisulfite solution rapidly destroys hydroperoxides but does not destroy peroxides completely. The hydroperoxides and peroxides decomposed extensively during attempted distillation at about 1 mm. of Hg partial vacuum. We had some success in concentration by liquid chromatography over silica gel the unconverted olefins are eluted with n-hexanes, and a hydroperoxide-peroxide... 

Aluminosilicates are the active components of amorphous silica—alumina catalysts and of crystalline, well-defined compounds, called zeolites. Amorphous silica—alumina catalysts and similar mixed oxide preparations have been developed for cracking (see Sect. 2.5) and quite early [36,37] their high acid strength, comparable with that of sulphuric acid, was connected with their catalytic activity. Methods for the determination of the distribution of the acid sites according to their strength have been found, e.g. by titration with f-butylamine in a non-aqueous medium using adsorbed Hammett indicators for the H0 scale [38],... 

Silica, alumina, and silica-alumina surfaces are of great importance for catalysis and chromatography. Reactivity of these materials is determined by the structure of the surface and its relative acidity, and considerable effort is being expended to characterize it. Of particular interest are the surface hydroxyl groups. Among the methods used for their study the most powerful are IR spectroscopy and titration with acid-base indicators. Conventional NMR can cope with the observation of adsorbed species, where a considerable amount of motional averaging is present MAS NMR must be used to study the surface directly. 

Take et al. (69) extended the acid strength range of the n-butylamine titration method. They employed indicators such as 4-nitrotoluene (pKa = - 10.5) and 2,4-dinitrotoluene (pKa = - 12.8), which are considerably less basic than the other Hammett indicators used to measure surface acidity. Endpoints were determined spectrophotometrically. These authors found that the acid sites on silica-alumina catalyst had an acid strength corresponding to an H0 between - 10.5 and - 12.8 a few sites had even higher acid strengths (H0 < 12.8). Strong acid sites were eliminated when silica-alumina was poisoned with sodium ions. 

Tanabe et al. (142, 143) find that silica-titania is highly acidic and has high catalytic activity for phenol amination with ammonia and for double-bond isomerization in butenes. Its acidity determined by n-butylamine titration varies with pretreating temperature and catalyst composition. The highest acidity per unit weight of catalyst was obtained when Ti02-Si02 (1 1 molar ratio) was heated at 500°C. 

However it is now clear that acid strength is not a singlevalued function, that different kinds of bases will tend to rank acid strengths differently, depending on their "hardness" or "softness". This is illustrated by the work of Kobayashi (13), who used a spectroscopic method of determining [B]/[BH+] on a sample of silica-alumina titrated with n-butylamine and one titrated with pyridine (Figure 2). Evidently the acidity of indicators and of individual acid sites on solids needs at least two constants for complete characterization of acid strength. 

Nitrogen in organosilicon compounds can be determined by the standard Kjeldahl method. Both silicon and nitrogen can be determined on the same sample by digesting it in concentrated sulfuric acid to which a drop of mercury has been added 18 the silica is filtered from the diluted acid, and ammonia is distilled from the filtrate after alkali sulfide and caustic solution have been added. The distilled ammonia is absorbed in standard acid, and the excess of acid is titrated in the usual manner. 

Selective chemisorption methods have been used with success for the determination of metal surface area and particle size in supported catalysts, and for titration of acid sites on silica-alumina and zeolite catalysts. The chemisorption methods are sometimes neglected in the quest for a more physical description of the catalyst surface, possibly with the penalty of missing an important and quantitative piece of information about the catalyst surface. 

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