Titration method

Titration Methods. - The procedure whereby oxygen is chemisorbed on the metal surface and removed by titration with hydrogen (or the converse) is often used despite the continuing debate about the stoicheiometries involved. Before the period under review, those proposed were  

Buyanova, O. F. Zapreeva, and A. P. Karnaukhov, Kinet. Catal. (USSR), 1978 

Dalla Betta and M. Boudart, Proc. 5th Internat. Congress on Catalysis , Miami 

For RU-AI2O3 good agreement between H2-O2 titration, CO adsorption, and electron microscopy was found and also between the titration method and CO adsorption for Pd-Si02 catalysts.  

Netzer and H. L. Gruber, Z. Phys. Chem. Neue Folge, 1975, 96, 25. 

By analogy to pH titration curves of acids and bases, it is customary in precipitation titrations to plot the quantity pM (defined by either — log [M ] or — log a m ) against titration volume. For certain metals that form reversible electrodes with their ions, the measured electrode potential is a linear function of the logarithm of ion activity, so the titration curve can be realized experimentally in a potentiometric titration. In any case, the curve gives a useful indication of the sharpness of an endpoint break. 

As it was for acid-base titrations, the concept of relative precision (Section 3-7) is useful for comparing the steepness of titration curves in the immediate vicinity of the end point. For the formation of a precipitate of symmetrical charge type (m = n), with activity coefficients assumed to be unity. 

It is often assumed that in a I I ion combination titration the point of maximum slope (inflection point) coincides with the equivalence point. This assumption would be correct only if no dilution occurred during titration. Meites and Goldman and Carr showed that the inflection point slightly precedes the equivalence point when dilution is taken into account. This efiect of dilution is rarely the limiting factor in end-point predsion and is an unnecessary complication under virtually all practical conditions. It becomes significant when the concentration is low or the solubility product is large thus the error is about 1 ppt for the titration of a 10 Af solution of a substance with a 10 M titrant when the solubility product is 10 °. The effect can be minimized by use of a titrant with a high concentration compared with that of the substance titrated. 

For precipitates of asymmetrical charge types, such as MA2 and MjA, expressions for relative precision are more complicated. Christopherson, excluding the effect of dilution, indicated that the relative titration error, defined by ( inflection — V)IV (where inflection is the titrant volume to the inflection point and V is the equivalence-point volume), is generally 

For detailed explanations of the chemistry of specific prreipitation titrations the reader is referred to other sources. These include methods such as the Mohr method for halides using the silver chromate end point, the Fajans adsorption indicator method, the Volhard method for FeSCN end point, the titration of halide mixtures with the attendant solid-solution and adsorption effects, the titration of fluoride with thorium(IV), and the titration of sulfate with barium ion. 

FIGURE 5.18 The determination of proton surface charge from potentiometric data by comparing a titration of the colloidal suspension (squares) with one of the support electrolyte alone (circles). 

In the ideal case, the volume difference AV, the amount of additional base solution employed to bring the colloidal particles to a given pH, is directly related to the OH- sorbed by the colloid, thus 

The sign would be reversed in a titration with an acid reagent there are also several variants in the experimental procedure (Kosmulski 2009). An alternative to the use of blank titrations, if the solution composition is well known, is to dednce Opj from a charge balance, such as (Body et al. 2001), 

Taking into account the presence of acid or base imparities, the true surface charge is 

FIGURE 5.19 Variation of surface charge as a function of solution pH for /-AljOj at different concentrations of NaCl. (Reprinted from J. Colloid Interface Sci., 127, Spryeha, R., Electrical double layer at alumina/electrolyte interface 1. Surface charge and zeta potential, 1-11. Copyright 1989, with permission from Elsevier.) 

The strength of the basic sites can be expressed on a scale given by the H function defined by the equation 

According to Andersen and F0yn (1969), the method is not specific for H2S since the results will also include the effects of other reductants. In fact, this may provide a better measure of the true oxygen deficiencies in the water studied and might therefore be of primary interest in conjimction with biological problems. 

Note For work in coastal areas, some oxygen titration methods include addition of sodium azide to the reagents to avoid effects of possible contaminants. In this case, the titration method for hydrogen sulphide using the oxygen reagents will not work, because the azide will react with hydrogen sulphide. 

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Initial attempts at developing precipitation titration methods were limited by a poor end point signal. Finding the end point by looking for the first addition of titrant that does not yield additional precipitate is cumbersome at best. The feasibility of precipitation titrimetry improved with the development of visual indicators and potentiometric ion-selective electrodes. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

Titration methods using adsorption indicators, based on the precipitation of insoluble iodides, have also been proposed (81—84). The sensitivity of these methods is less than that for the thiosulfate titration. Electrometric titration of the reaction between iodine and thiosulfate (85) was not found to be practicable for routine deterrninations of minute quantities of iodine. 

The double titration method, which involves the use of ben2ylchloride, 1,2-dibromoethane, or aUyl bromide, determines carbon-bound lithium indirectly (101,102). One sample of the //-butyUithium is hydroly2ed directly, and the resulting alkalinity is determined. A second sample is treated with ben2ylchloride and is then hydroly2ed and titrated with acid. The second value (free base) is subtracted from the first (total base) to give a measure of the actual carbon-bound lithium present (active base). 

A titration method for primary and secondary nitroparaftins uskig hypochlorite gives good accuracy ( 0.1%) (84). It is based on the foUowkig equation ... 

Phosphoms content usually is measured by a double end point titration method in which a 1.0-g sample is dissolved in a hot HNO —H2SO4—HCIO4 mixture. The pH is adjusted to 2.5 with NaOH, and the resulting H PO is titrated with 0.5-A[ NaOH, using an automatic titrator. The titer between the first and second end points is used to quantify the phosphoms as H PO. ... 

The mixture is kept for 3 hours at 105°C after the oxide addition is complete. By this time, the pressure should become constant. The mixture is then cooled to 50°C and discharged into a nitrogen-filled botde. The catalyst is removed by absorbent (magnesium siUcate) treatment followed by filtration or solvent extraction with hexane. In the laboratory, solvent extraction is convenient and effective, since polyethers with a molecular weight above about 700 are insoluble in water. Equal volumes of polyether, water, and hexane are combined and shaken in a separatory funnel. The top layer (polyether and hexane) is stripped free of hexane and residual water. The hydroxyl number, water, unsaturation value, and residual catalyst are determined by standard titration methods. 

Chemical analysis methods maybe used for assay of silver alloys containing no interfering base metals. Nitric acid dissolution of the silver and precipitation as AgCl, or the Gay-Lussac-VoUiard titration methods are used iaterchangeably for the higher concentrations of silver. These procedures have been described (4). 

Test Method for Sulfur in Graphite by Combustion—lodometric Titration Method... 

Metal Content. Two common analytical methods for determining metal content are by titration and by atomic absorption spectrophotometry (aas). The titration method is a complexiometric procedure utilizing the disodium salts of ethylenediaminetetraacetic acid (EDTA). The solvent, indicator. 

Sulfur Dioxide EPA Method 6 is the reference method for determining emissions of sulfur dioxide (SO9) from stationary sources. As the gas goes through the sampling apparatus (see Fig. 25-33), the sulfuric acid mist and sulfur trioxide are removed, the SO9 is removed by a chemical reaction with a hydrogen peroxide solution, and, finally, the sample gas volume is measured. Upon completion of the rim, the sulfuric acid mist and sulfur trioxide are discarded, and the collected material containing the SO9 is recovered for analysis at the laboratory. The concentration of SO9 in the sample is determined by a titration method. 

Determination of water of different materials is one of the important tasks of the analytical chemistry. For water determination in organic solvents physical-chemical methods use side by side with the classic titration method by Karl Fisher. In particular, gas chromatography (GC), distinguished its universality and selectivity, is used. However, GC usually used for determination of relatively large quantity of water. 

Checking the bath concentration The concentration of bath solution in caustic-based cleaners can be checked by a simple titration method as noted below, while for the remaining types of cleaners, a visual check of the degreased surfaces will be sufficient. The titration method is as follows ... 

For the estimation of ephedrine in its salts or simple solutions, titration methods and a Kjeldahl estimation have been described by various authors. The formation of iodoform from ephedrine has been proposed as a method of estimation by Sanchez, and biological methods have been used by several authors. ... 

Titrations-fliissigkeit, /. titration solution, -verfahren, n. titration method, -wert, m. titration value. 

Titrier-flasche,/. titration bottle (for feeding a buret), -fliissigkeit, /. titrating solution, standard solution, -gerate, n.pl. titrating apparatus, -methode, /. titration method, volumetric method, -saure, /. titrating acid, standard acid. 

Alkalinity and Lime Content. The whole mud alkalinity test procedure is a titration method which measures the volume of standard acid required to react with the alkaline (basic) materials in an oil mud sample. The alkalinity value is used to calculate the pounds per barrel unreacted excess lime in an oil mud. Excess alkaline materials, such as lime, help to stabilize the emulsion and also neutralize carbon dioxide or hydrogen sulfide acidic gases. 

The comparison of more than two means is a situation that often arises in analytical chemistry. It may be useful, for example, to compare (a) the mean results obtained from different spectrophotometers all using the same analytical sample (b) the performance of a number of analysts using the same titration method. In the latter example assume that three analysts, using the same solutions, each perform four replicate titrations. In this case there are two possible sources of error (a) the random error associated with replicate measurements and (b) the variation that may arise between the individual analysts. These variations may be calculated and their effects estimated by a statistical method known as the Analysis of Variance (ANOVA), where the... 

It should be noted that in this example the performance of only one variable, the three analysts, is investigated and thus this technique is called a one-way ANOVA. If two variables, e.g. the three analysts with four different titration methods, were to be studied, this would require the use of a two-way ANOVA. Details of suitable texts that provide a solution for this type of problem and methods for multivariate analysis are to be found in the Bibliography, page 156. 

The direct iodometric titration method (sometimes termed iodimetry) refers to titrations with a standard solution of iodine. The indirect iodometric titration method (sometimes termed iodometry) deals with the titration of iodine liberated in chemical reactions. The normal reduction potential of the reversible system ... 

A number of methods have been proposed for the detection of rancidity. The determination of active oxygen consists of dissolving the fat in a suitable medium such as chloroform and acetic acid, adding potassium iodide, and titrating the liberated iodine with a standard thiosulfate solution (16, 20). This is perhaps the most widely used method at the present time. Another procedure which has been proposed for the detection of peroxides employs ferrous ammonium sulfate and ammonium thiocyanate in acetone. The resulting red color of ferric thiocyanate is measured spectrophotometrically, and is said by the authors to yield more reproducible results than do the usual titration methods (21). 

Application of the Nonaqueous Titration Method to Organic Compounds of Ordnance Interest , PATM 31 (1953) 30b) Ibid, A ... 

Nonaqueous Titration Method for the Determination of the Purity of Ammonium Picrate ,... 

Nonaqueous Titration Methods. See under Nitrogen Determination in Energetic Materials in this Vol... 

The titration method used is, in our experience, incapable of detecting a difference between a reaction rate of this speed or one a hundred times slower, since it takes a minimum of 45 sec to obtain the first reading. Since this is the major point on which the high r factor was based, the arguments following from it are no longer tenable. 

The beaker is chilled in an ice bath for 1 hour. The crystalline diacetate that separates is collected on a Buchner funnel and washed with three 20-ml. portions of cold water. After drying for 30 minutes on the funnel with suction, the diacetate is dried overnight in a vacuum desiccator containing calcium chloride (Note 4). The dried diacetate weighs 26.7-29.3 g. (83-91%) and melts at 158-159° with decomposition. The purity of the diacetate, determined by the titration method of Lucas, Kennedy, and Formo,3 is 97-98%, which is good enough for most purposes. The purity can be increased to 99-100% by a recrystallization from 5M acetic acid. 

Subsequent tables cover important titration methods (Table 17), useful 13C-NMR data for the analysis of LAB/LAS (Table 18), molecular fragments of alkylbenzenes (Table 19), and characteristic infrared absorption bands of an LAB/LAS molecule (Table 20). 

TABLE 17 Titration Methods for the Determination of Anionic Surfactants... 

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