Titration displacement

TITRATION OF ANIONS OF WEAK ACIDS WITH STRONG ACIDS DISPLACEMENT TITRATIONS 10.17... 

Titration of borate ion with a strong acid. The titration of the tetraborate ion with hydrochloric acid is similar to that described above. The net result of the displacement titration is given by ... 

Diphenylcarbazide as adsorption indicator, 358 as colorimetric reagent, 687 Diphenylthiocarbazone see Dithizone Direct reading emission spectrometer 775 Dispensers (liquid) 84 Displacement titrations 278 borate ion with a strong acid, 278 carbonate ion with a strong acid, 278 choice of indicators for, 279, 280 Dissociation (ionisation) constant 23, 31 calculations involving, 34 D. of for a complex ion, (v) 602 for an indicator, (s) 718 of polyprotic acids, 33 values for acids and bases in water, (T) 832 true or thermodynamic, 23 Distribution coefficient 162, 195 and per cent extraction, 165 Distribution ratio 162 Dithiol 693, 695, 697 Dithizone 171, 178... 

In principle, any type of titration can be carried out conductometrically provided that during the titration a substantial change in conductance takes place before and/or after the equivalence point. This condition can be easily fulfilled in acid-base, precipitation and complex-formation titrations and also the corresponding displacement titrations, e.g., a salt of a weak acid reacting with a strong acid or a metal in a fairly stable complex reacting with an anion to yield a very stable complex. However, for redox titrations such a condition is rarely met. 

In Fig. 2.6, curve I illustrates the displacement titration of CH3COONa with HC1 according to... 

In fact, any type of titration can be carried out potentiometrically provided that an indicator electrode is applied whose potential changes markedly at the equivalence point. As the potential is a selective property of both reactants (titrand and titrant), notwithstanding an appreciable influence by the titration medium [aqueous or non-aqueous, with or without an ISA (ionic strength adjuster) or pH buffer, etc.] on that property, potentiometric titration is far more important than conductometric titration. Moreover, the potentiometric method has greater applicability because it is used not only for acid-base, precipitation, complex-formation and displacement titrations, but also for redox titrations. 

In connection with the above, we shall still consider the pH curves of the displacement titrations, because in fact they represent a back-titration of an alkaline reacting salt (e.g., NaA) with a strong acid or of an acidic reacting salt (e.g., MX) with a strong base, so that in Fig. 2.19 the foregoing data of equivalence point and initial point are of direct application. 

Sigurskjold, B.W., C.R. Berland, and B. Svensson. 1994. Thermodynamics of inhibitor binding to the catalytic site of glucoamylase from Aspergillus niger determined by displacement titration calorimetry. Biochemistry 33 10191-10199. 

Iodine displacement titrations are used in pharmacopoeial assays of liquefied phenol, methyl hydroxybenzoate, propyl hydroxybenzoate and phenidione. 

Hg2+ does not have a satisfactory indicator, but a displacement titration is feasible. Hg2+ is treated with excess Mg(EDTA)2- to displace Mg2+, which is titrated with standard EDTA. 

For end-point detection, we commonly use metal ion indicators, a glass electrode, an ion-selective electrode, or a mercury electrode. When a direct titration is not suitable, because the analyte is unstable, reacts slowly with EDTA, or has no suitable indicator, a back titration of excess EDTA or a displacement titration of Mg(EDTA)2- may be feasible. Masking prevents interference by unwanted species. Indirect EDTA titrations are available for many anions and other species that do not react directly with the reagent. 

Describe what is done in a displacement titration and give an example. 

The ability to bind to DNA was studied by ethidium bromide displacement titrations. The phosphodiester backbone of DNA was fully stable in the presence of the coordination compounds. The apparent binding constants were dependent on the charge of the macrocycles. Apparent binding constants of the metal complexes were even stronger and co-operative effect could be observed for the dinuclear ligands. 

In displacement titrations, an unmeasured excess of a solution containing the magnesium or zinc complex of EDTA is introduced into the analyte solution. If the analyte forms a more stable complex than that of magnesium or zinc, the following displacement reaction occurs ... 

Displacement titrations are used when no indicator for an analyte is available. 

Challenge Calculate the equilibrium constant for Reaction 13-3 if = Hg. Why is Mg(EDTA) " used for a displacement titration ... 

Figure 3.3 High-frequency (A) and potentiometric (B) displacement titration of the monosodium salts of the monomethyl esters of poly(itaconic acid-co-styrene). Titration of 0.2345 g 57 43 anhydride-styrene copolymer + MeOH (heat) + excess NaOH with 0.1286 N HCl. Reproduced with permission from J. Douglas, A. Timnick and R.L. Gvi t, Journal of Polymer Science Part A General Papers, 1963,...

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