Experimental Conditions Titration

FIGURE 2.6 Determination of AV (Equation 2.10) from potentiometric titration data (correction for inert electrolyte titration). 

The apparent (in C/m ) is obtained from Equation 2.10 or 2.11. The surface charge density can also be expressed as charge per unit mass (in C/g) [523,524], especially when A is not available. The two representations (charge per unit mass or per unit surface area) produce different numerical values of charge density but the same PZC. In [525] and other papers from the same research group, the surface charge density is expressed as Z, the number of protons reacted per surface site. Z = 0 in their terminology is not necessarily the PZC [75]. Such results can be obtained when the number of surface sites per unit mass or per unit surface area is known. 

FIGURE 2.7 Correction for acid or base associated with solid particles (Equation 2.12). 

The same symbol is used for corrected (Equation 2.10) and uncorrected (Equation 2.12) Og, and the details of data handling are seldom reported in the experimental parts of scientific papers. A few publications report PZCs obtained by titration without clear explanations of whether they were obtained as CIPs or if titration was performed at only one ionic strength. Such results are indicated as Titration in the Method columns of the tables in Chapter 3. A few methods that give a PZC equivalent to that from the potentiometric titration method are described in Section 2.8.4. 

1 The Choice oe an Inert Electrolyte and the Range oe Ionic Strengths 

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Figure 4.25 Effect of beta-adrenergic blocking drugs (therapeutically used compounds) on ANS fluorescence in human erythrocyte ghosts. Experimental conditions titration with drugs, ANS 10 M, ghosts 2 mg protein/ml buffer pH 7.0. From Wiethold et al. [207] with permission.

It is now reported by P. Szabo that the quercitols can be titrated with completely normal results, by using suitable experimental conditions, and especially low temperature and low pH, for the titrations (40,41). This method might also be applicable to the estimation of the tetrols. 

Running a blank determination. This consists in carrying out a separate determination, the sample being omitted, under exactly the same experimental conditions as are employed in the actual analysis of the sample. The object is to find out the effect of the impurities introduced through the reagents and vessels, or to determine the excess of standard solution necessary to establish the end-point under the conditions met with in the titration of the unknown sample. A large blank correction is undesirable, because the exact value then becomes uncertain and the precision of the analysis is reduced. 

Discussion. Potassium may be precipitated with excess of sodium tetraphenyl-borate solution as potassium tetraphenylborate. The excess of reagent is determined by titration with mercury(II) nitrate solution. The indicator consists of a mixture of iron(III) nitrate and dilute sodium thiocyanate solution. The end-point is revealed by the decolorisation of the iron(III)-thiocyanate complex due to the formation of the colourless mercury(II) thiocyanate. The reaction between mercury( II) nitrate and sodium tetraphenylborate under the experimental conditions used is not quite stoichiometric hence it is necessary to determine the volume in mL of Hg(N03)2 solution equivalent to 1 mL of a NaB(C6H5)4 solution. Halides must be absent. 

An excess of a standard solution of iron(II) must therefore be added and the excess back-titrated with standard cerium(IV) sulphate solution. Erratic results are obtained, depending upon the exact experimental conditions, because of induced reactions leading to oxidation by air of iron(II) ion or to decomposition of the persulphate these induced reactions are inhibited by bromide ion in concentrations not exceeding 1M and, under these conditions, the determination may be carried out in the presence of organic matter. 

For good results, the following experimental conditions must be observed (1) the hydrochloric acid concentration in the final solution should be at least 4M (2) air should be displaced from the titration mixture by adding a little solid sodium hydrogencarbonate (3) the solution must be allowed to stand for at least 5 minutes before the liberated iodine is titrated and (4) constant stirring is essential during the titration to prevent decomposition of the thiosulphate in the strongly acid solution. 

The method based upon the reduction of iron(III) solutions in the presence of sulphuric acid, boiling, and subsequent titration in the cold with standard 0.02M potassium permanganate frequently yields high results unless the experimental conditions are closely controlled ... 

Thus, under suitable experimental conditions, all aromatic sulphones are cleaved, in most cases by a two-electron process summarized by equations 1 and 2. Such reactions have been established1-5 by means of coulometric titration, isolation of cleavage residues ArH and RH and chemical identification of the anion ArS02- (e.g. by treatment of the... 

Fig. 7. A comparison of the FTIR and EPR redox titrations of the D. gigas hydro-genase. Top panel FTIR titration based on the height of the low-frequency band. For experimental conditions, see (65). Bottom panel Calculated potentials obtained from EPR-monitor titration and the TED model (80). The vertical axis represents the proportion of a redox species.

Table 1. Comparison of polymer latexes obtained by emulsion polymerization of 1,4-DVB and S [79], Experimental conditions temperature = 50 °C volume ratio water to monomer = 6.25, SDS concentration = 0.02 M, PPS concentration = 0.01 M. Particle diameters were measured by soap titration and by electron microscopy.

Titration curve for seawater. The shape of the curve is dependent upon experimental conditions. The top curve is produced when seawater is titrated in an open container so that CO2 generated after incremental acid addition can escape into the atmosphere. The bottom curve is generated when seawater is titrated in a closed container. In this case, the pH drops faster during the initial part of the titration because of the build-up of CO2 as acid is added. Once the carbonate/carbonic acid equivalence point is reached, both curves converge upon the same pH for the same volume of acid added, but extensive laboratory work has demonstrated that better accuracy is achieved with the closed container method. Source From Pilson, M. E. Q. (1998). An Introduction to the Chemistry of the Sea. Prentice-Hall, p. 119. 

Tetralin hydroperoxide (1,2,3,4-tetrahydro-l-naphthyl hydroperoxide) and 9,10-dihydroanthracyl-9-hydroperoxide were prepared by oxidizing the two hydrocarbons and purified by recrystallization. Commercial cumene hydroperoxide was purified by successive conversions to its sodium salt until it no longer increased the rate of oxidation of cumene at 56°C. All three hydroperoxides were 100% pure by iodometric titration. They all initiated oxidations both thermally (possibly by the bi-molecular reaction, R OOH + RH — R O + H20 + R (33)) and photochemically. The experimental conditions were chosen so that the rate of the thermally initiated reaction was less than 10% of the rate of the photoreaction. The rates of chain initiation were measured with the inhibitors 2,6-di-ter -butyl-4-methylphenol and 2,6-di-fer -butyl-4-meth-oxyphenol. None of the hydroperoxides introduced any kinetically first-order chain termination process into the over-all reaction. 

Studies on the formation of polymer chelates have been almost exclusively concerned with the Cu(II) ion. The reasons are (i) the stability of Cu(II) chelates in an aqueous solution is sufficient to make them difficult to hydrolyze under experimental conditions (ii) Cu(II) ions can be readily determined by chelate titration, atomic absorption spectrophotometry, etc. (iii) Cu(II) chelates are active in both visible and ESR spectra. 

Consider, for example, the titration of sodium tetraborate solution with a diol and suppose the following experimental conditions are met (Na+) >> (H+) and that (D ) >> (B ), where D and B are the total diol and boron concentrations respectively (e.g., 0.01M Na2B407, 0.1—1M diol, and between pH 4-8). Applying these conditions to the conservation equations, XI becomes... 

Figure 1 shows a comparison of the model results with the experimental results. The three curves shown in the plot correspond to three different values of the rate constant for the HOSO + O2 reaction upper - 8 x 10-13, middle - 4 x IO13, and lower - 2 x 10"13 cm3/s. Similar comparisons between model and experimental results have been made for a wide variety of other experimental conditions. Based upon such comparisons, we have concluded that a rate constant of (4 )x lu-13 cm3/s gives the best match between the experimental and model results, in both an absolute sense and based upon the shape of the O2 titration results. Since there is greater uncertainty in the absolute concentrations of HO radicals than there is in the trend of the HO concentrations with increasing O2, the comparison of the shapes of the experimental and model O2 titration profiles may provide a reliable basis for comparison. 

Figures 3 and 4 illustrate that there is a temperature dependence in acid formation under our experimental conditions because Figure 3 shows —59 mmoles of acid at the end of aldehyde oxidation whereas Figure 4 shows only 50 mmoles of acid. However, temperature dependence occurs only in the aldehyde-oxidation phase since the two plots for acid formation before ozone breakthrough are essentially identical. Furthermore, the temperature of ozonization does not affect final acid formation if the solutions are allowed to warm up with no immediate triethylamine treatment. Thus, upon warming to room temperature the final acid values for 0° and — — 25 °C. titration experiments are in the range 65-70 mmoles total acid. (In the —25°C. titration experiments care was taken to treat the cold ozonized cement with triethylamine as soon as the cement was removed from the reactor. The cement was not allowed to warm up before triethylamine treatment. As discussed later, triethylamine reduces a species which is capable of forming acid.)...

The equilibrium constants involved in the reaction Fe3+ + 3 cat2" Fe(cat)33- were determined as follows. An aqueous solution of Fe3+ (5.5 X 10-3M) and catechol (1.48 X 10-2M), initially made basic with the addition of KOH, was titrated with 1.24M HC1 under an oxygen-free atmosphere at 22° and ionic strength (KC1) 0.16-0.22M (Figure 12). The acid dissociation constants for catechol were determined independently (under similar experimental conditions) to be pKai = 9.38 and... 

Fractional precipitation The calculation as to which of two sparingly soluble salts will be precipitated under given experimental conditions may be also made with the aid of the solubility product principle. An example of great practical importance is the Mohr method for the estimation of halides. In this process a solution of chloride ions is titrated with a standard solution of silver nitrate, a small quantity of potassium chromate being added to serve as an indicator. Here two sparingly soluble salts may be formed, viz. silver chloride (a white precipitate) and silver chromate (which is red) ... 

The soft experimental conditions in the synthesis of P-CDAPS were optimized using experimental design. The hybrid precursor P-CDAPS has been characterized in order to determine its structure. ETIR spectra show the presence of amino groups (1564cm ) on one hand and siloxane structure (1100-1000cm ) on the other hand, conhrmed by TGA measurements. This TGA gave a Si ratio of 5.80 0.04%., conhrmed by elemental analysis. N content was determined by elemental analysis at 2.98 0.02%, which corresponds to 2.13 0.04mmol/g of amine functions, also deduced from amine titration. 

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