Alkalimetric Titrations

If we add a solution of the disodium salt of EDTA to an accurately neutralized solution of the metal cation to be titrated, the anticipated complex is formed with the liberation of two protons  

The liberated protons may be titrated with a solution of sodium hydroxide in the presence of an acid-base indicator or with a pH-metric indication. Alternatively, one may use the iodate-iodide reaction with profit. A solution of the iodate-iodide 

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D. Alkalimetric titration. When a solution of disodium ethylenediaminetetra-acetate, Na2H2Y, is added to a solution containing metallic ions, complexes are formed with the liberation of two equivalents of hydrogen ion ... 

The solution of the metal to be determined must be accurately neutralised before titration this is often a difficult matter on account of the hydrolysis of many salts, and constitutes a weak feature of alkalimetric titration. 

In an ideally designed experiment, only a single titration is needed to determine the solubility constant and the aqueous pKa. This is possible when the amount of sample, such as a weak base, added to solution is such that from the start of an alkalimetric titration (pH [Pg.104]

Compare the alkalimetric titration of a polyprotic acid (e.g., polyaspartic acid) with that of an Al203 dispersion show in either case the effect of the presence of a metal ion (e.g., Cu2+) on the titration curve. 

Comparison of an alkalimetric titration curve of an equimolar (1 O 4 M) solution of acetic acid (pK = 4.8) and phenol (pK = 10) with a humic acid that contains 10 4 M carboxylic groups. 

A comparison with the reversible interface can be made. The reversible solid electrolyte interface can be used in a similar way to explore the distribution of charge components at solid-water interfaces. As we have seen, the surface charge density, o, (Eqs. (3.1) and (iii) in Example 2.1) can be readily determined experimentally (e.g., from an alkalimetric titration curve). The Lippmann equations can be used as with the polarized electrodes to obtain the differential capacity from... 

The BNC can be defined by a net proton balance with regard to a reference level -the sum of the concentrations of all the species containing protons in excess of the reference level, less the concentrations of the species containing protons in deficiency of the proton reference level. For natural waters, a convenient reference level (corresponding to an equivalence point in alkalimetric titrations) includes H20 and H2C03 ... 

Starting with [Cr(Hedta)(OH2)], alkalimetric titration gives pK as 2.10 (97), and from [Cr(edta)], a similar titration gives pK = 7.42 (98). The questions under debate are (i) what is the coordination number of the edta ligand bound to Cr(III) in the pH range 4-7, and (ii) if the ligand is hexadentate, can a seventh position in the inner coordination sphere be occupied by a water molecule The latter proposal is not unreasonable, as 7-coordination is observed in the solid-state hexaden-... 

In a definitive series of experimental investigations H. N. Wilson showed that the quinolinium salt, (C isNJ fPCV I2M0O3]3- was anhydrous, contained exactly 12 moles of molybdenum trioxide per mole of phosphate, that the precipitate had a negligible solubility and could be dried to constant weight in two hours at 105 °C. This precipitate also lent itself to a precise alkalimetric titration. In the presence of citric acid interference by silica was inhibited so that the method was admirably suitable for the analysis of basic slags or fertilizers.34... 

Coagulant. Stock solutions were 10"2Af in reagent grade A1(C104)3 and 10-1M in HC104. Aluminum determinations for the standardization of stock solutions were made by alkalimetric titration. The amount of residual dissolved aluminum in adsorption experiments was determined absorptiometrically using aluminon (14). The agreement between both... 

The methods most commonly used for the quantitative assay of / -lactamase are based on one of the following principles (1) Manometric or alkalimetric titration of the new carboxyl group formed by hydrolysis of the /3-lactam ring (2) iodometric titration of the product, and (3)... 

The determination of partition caefcients by the potentiometric method is part of the function of the Sirus PCA101 (Avdeef, 1993). Typically, a preacidiLed solution of a weak acid is alkalimetrically titrated to some appropriately high pH the partition solvent such as octanol is then added, and the dual-solvent mixture is acidimetrically titrated back to the starting pH. Analysis of the two titration curves will yield two fKgS pl< and pol, where pdQ, is the apparent constant derived from... 

The oxidations usually are carried out at room temperature with an excess of periodic acid or its salts. The analyses can be completed by several means. The lUPAC procedure for glycerol involves an alkalimetric titration of the formic acid generated, using a pH of 8.0 at the end point. More commonly, the excess periodate is determined by adding a slight excess of standard As(III) to reduce periodate to iodate then the excess As(III) is titrated with standard iodine. Both iodate and periodate can be determined by first masking the periodate with molybdate while iodate is titrated and then demasking the periodate with oxalate, followed by titration of the periodate. ... 

The principles outlined above can readily be extended to multiprotic acids. The alkalimetric titration of an acid H2L added as the salt H2L X (e.g., an amino acid, RNH2COOH = HL) is given by the electroneutrality condition... 

Figure 3.11. Alkalimetric titration of a weak acid (10 M boric acid), (a) Equilibrium distribution, (b) Buffer intensity, (c) Alkalimetric titration. No pH jump occurs at the equivalence point (/ = 1) because of buffering by OH ions.

Figure 3.13. Comparison of alkalimetric titration of an equimolar (10 M) acetic acid (pKa = 4.8) and phenol (p = 10) with titration of humic acid containing 10 mol carboxylic groups.

Figure 4.7. Conservative quantities alkalinity and acidity as acid-neutralizing and base-neutralizing capacity. These parameters can be determined by acidimetric and alkalimetric titration to the appropriate end points. The equations given below define the various capacity factors of an aqueous carbonate system rigorously. If the solution contains protolytic systems other than that of aqueous carbonate, these equations have to be corrected for example, in the presence of borate one has to add [B(OH).Tl to the right-hand side of equation 3 and IH3BO3] to the right-hand side of equation 6.

Titration to the intermediate equivalence point y (f = 1) is a measure of the CO2 acidity in an alkalimetric titration and of p-alkalinity in an acidimetric titration. 

The alkalimetric titration of H2CO with a strong base, Cb, is given by... 

Figure 4.11. Alkalimetric titration of an acid rainwater with a pH = 4.26, consisting of a mineral acidity of [H-Acy] = 50 /xeq iiter and a weak acidity of 90 /xeq liter ([NH/] = 85 /iM and acetic acid [HA] = 5 fiM). COj has been expelled with N2 prior to the titration. In the conventional titration curve, the pH jump is equivalent to the mineral acidity [H-Acy]. If only mineral acidity (no weak acids) were present, the titration curve would correspond to the drawn-out line (a). The Gran titration procedure permits one to distinguish between total acidity [Acyj] (end point 2) = 140 /ieq liter" and mineral acidity, [H-Acy] (end point e ) = 50 ieq liter". (Adapted from Sigg and Stumm, 1994.)...

Br nsted Acidity and Lewis Acidity In Figure 6.2 alkalimetric titration curv es for the reaction of phosphoric acid and Fe(H20>6, respectively, with a base (OH ion) are compared. Millimolar solutions of H3PO4 and feiric perchlorate have a similar pH value. Both acids (Fe aq and H3PO4) are multiprotic acids that is, they can transfer more than one proton. 

Figure 6.2. Alkalimetric titration of 10 M H3PO4 and 10" M Fe aq. Both H3PO4 and Fe aq are multiprotic Br nsted acids. Millimolar solutions of H3PO4 and Fe(C104>3 similar pH values.

Figure 9.7. Titration of a suspension of a-FeOOH (goethite) in the absence of specifically adsoibable ions, (a) Acidimetric-alkalimetric titration in the presence of an inert electrolyte, (b) Charge calculated fix>m the titration curve (cluuge balance), (c) Microscopic acidity constants calculated from (a) and (b). Extrapolation to charge zero gives intrinsic and pA. (Data from Sigg and Stumm, 1981.)...

Figure 14.7. (a) Electrophoretic mobility and (b) surface charge of 7-AI2O3 in presence of 10 M NaCl. Surface charge data from alkalimetric titration curve. (Data from Stumm et al., 1970.)... 

The specific adsorption of H, OH, cations, and anions on hydrous oxides and the concomitant establishment of surface charge can be interpreted in terms of the formation of surface complexes at the oxide-water interface. The fixed charge of the solid surface and the pH of its isoelectric point can be measured experimentally by determining the proton balance at the surface (from alkalimetric titration curve) and by the analytical determination of the extent of adsorbate adsorption. Equilibrium constants established for the surface coordination reactions can be used to predict pHiEp, to calculate adsorption isotherms, and to estimate concentration-pH regions for which the hydrous oxide dispersions are stable from a colloid-chemical point of view. 

Figure 6. Adsorption of aqueous silica on goethite (a-FeOOH) and its effect on the alkalimetric titration curve and su ace charge.

The charge vs. pH Curves 1 and 2 were calculated from alkalimetric titration curves of AUOs in the absence and presence of phthalic acid, respectively. The adsorption of total phthalic acid (formation of =AIXH and =AIX ) was determined analytically (Curve 3). Curve 4 was calculated from Curves 1 and 3 assuming that uncharged =AIXH only is formed. Curve 5 was calculated with the equilibrium constants given in Equation 24, the acidity constants of phthalic acid (—log Ko = 2.8, —log Kag = 4.9) (19). 

The fixed charge is computed from alkalimetric titration curves and from analytical determination of the quantity of adsorbed. For the electrophoretic mobility measurement (bottoma ratio of P /FeOOH equal to that of the lower charge vs. pH curve (top) was used (equilibrium values of P in solution are approximately the same) (IS), (top) (O) Pt = 2 X 1.2 g FeOOHf... 

The alkalimetric titration curve (a) permits the calculation of the surface charge as a function of pH (c) caused by the disturbance of the proton balance and the microscopic acidity constants as a function of the charge (b) intrinsic constants are obtained by extrapolation to zero surface charge (b). With the help of Equation 26, the surface potential either as a function of charge (d) or pH may be calculated. Experimental data are for y-AhOs in NaClOi solutions (17). 

Alkalimetric titration Powdered tablets equivalent to 50 - 200 mg of glafenine are placed in 150 mL conical flask. 25 mL of 0.1N HCi are added and shaken for 2 - 3 minutes. The bromocresol green indicator is added to the mixture (2 - 3 drops) and titration is carried out with 0.1 N NaOH. The indicator colour changes from yellow to bluish green at the end point. This method could be adopted for different dosage forms determination. Each mL of 0.1 N HCI volumetric solution is equivalent to 37.28 mg of glafenine (10). 

In analytical chemistry, where non-aqueous solvents are used in the acidimetric and alkalimetric titration of weak acids and bases, solvents are classified as acidic and basic [Gy 70]. In the former group the proton-donating and in the latter group the proton-accepting property predominates. Accordingly, bases can be titrated in acidic solvents, which readily transfer their protons to the base dissolved in them, and acids can be titrated in basic solvents, which readily accept protons from the acid dissolved in them. 

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