Chlorides using adsorption indicators

Thiocyanates may also be determined using adsorption indicators in exactly similar manner to chlorides and bromides, but an iron(III) salt indicator is usually preferred (Section 10.82). 

Table 11.1 lists some adsorption indicators. Fluorescein can be used as an indicator for any of the halides at pH 7 because it will not displace any of them. Dichlorofluoroscein will displace Cl" at pH 7 but not at pH 4. Hence, results tend to be low when titrations are performed at pH 7. Titration of chloride using these indicators is called Fajans method. Fluorescein was the original indicator described by Fajans, but dichlorofluoroscein is now preferred. Eosin cannot be used for the titration of chloride at any pH because it is too strongly adsorbed. 

For the titration of chlorides, fluorescein may be used. This indicator is a very weak acid (Ka = ca lx 10-8) hence even a small amount of other acids reduces the already minute ionisation, thus rendering the detection of the end point (which depends essentially upon the adsorption of the free anion) either impossible or difficult to observe. The optimum pH range is between 7 and 10. Dichlorofluorescein is a stronger acid and may be utilised in slightly acid solutions of pH greater than 4.4 this indicator has the further advantage that it is applicable in more dilute solutions. 

Either the Mohr titration or the adsorption indicator method may be used for the determination of chlorides in neutral solution by titration with standard 0.1M silver nitrate. If the solution is acid, neutralisation may be effected with chloride-free calcium carbonate, sodium tetraborate, or sodium hydrogencarbonate. Mineral acid may also be removed by neutralising most ofthe acid with ammonia solution and then adding an excess of ammonium acetate. Titration of the neutral solution, prepared with calcium carbonate, by the adsorption indicator method is rendered easier by the addition of 5 mL of 2 per cent dextrin solution this offsets the coagulating effect of the calcium ion. If the solution is basic, it may be neutralised with chloride-free nitric acid, using phenolphthalein as indicator. 

Similar remarks apply to the determination of bromides the Mohr titration can be used, and the most suitable adsorption indicator is eosin which can be used in dilute solutions and even in the presence of 0.1 M nitric acid, but in general, acetic (ethanoic) acid solutions are preferred. Fluorescein may be used but is subject to the same limitations as experienced with chlorides [Section 10.77(b)], With eosin indicator, the silver bromide flocculates approximately 1 per cent before the equivalence point and the local development of a red colour becomes more and more pronounced with the addition of silver nitrate solution at the end point the precipitate assumes a magenta colour. 

Discussion. The method is applicable to the determination of a mixture of two salts having the same anion (e.g. sodium chloride and potassium chloride) or the same cation (e.g. potassium chloride and potassium bromide). For example, to determine the amount of sodium and potassium chlorides in a mixture of the two salts, a known weight (Wj g) of the solid mixture is taken, and the total chloride is determined with standard 0.1 M silver nitrate, using Mohr s method or an adsorption indicator. Let w2 g of silver nitrate be required for the complete precipitation of Wj g of the mixture, which contains xg of NaCl and yg of KC1. Then ... 

Standard silver nitrate, 0.1N. Dissolve 16.989g of the salt in 1 liter of chloride-free water and standardize against pure NaCl using the adsorption indicator method... 

Ionic charges of the polymers were determined by photometric colloid titrations in some instances. A known amount of poly(diallyldimethylammonium chloride) was added to the polymer solution at a pH of 2.5. The excess poly(diallyldimethylammonium chloride) was titrated by poly(vinylsulfate) using the adsorption indicator methylene blue. The end point was detected by the photometric detector as the color of the solution changes from blue to violet. For anionic copolymers the colloid titration was conducted at pH values of 2.5 and 10.0 to determine the extent of modification. 

There is nothing new in principle about the use of isotopes as an aid to chemistry. For twenty years the radioactive elements have been used as indicators to study adsorption, solubility, volatility, distribution, and other phenomena of physical chemistry. Distribution of heavy radioactive atoms in plants has been studied through the relative amount of ionization found in the different parts. The ionization theory was supported by dissolving radioactive lead chloride in an aqueous solution of ordinary lead nitrate and then crystallizing out the lead chloride. The radioactive lead was found to be equally distributed between the two salts. In aqueous solution the two different kinds of lead are free to exchange anions, as predicted from the electrolytic dissociation theory. With un-ionized compounds of lead it was found that exchange does not take place. 

Fluorescein is a typical adsorption indicator that is useful for the titration of chloride ion with silver nitrate. In aqueous solution, fluorescein partially dissociates into hydronium ions and negatively charged fluoresceinate ions that are yellow-green. The fluoresceinate ion forms an intensely red silver salt. Whenever this dye is used as an indicator, however, its concentration is never large enough to precipitate as silver fluoresceinate. 

USE As an adsorption indicator in the determn of iodides in the presence of chlorides and bromides. The salts in dyeing and printing cotton, in printing half -silk, in dyeing jute, straw, etc,... 

Separation of apatite from dolomite using dodecylamine as the collector is enhanced by sodium chloride addition. Adsorption of the cationic collector on the apatite surface is attributed mostly to chemical Interactions. Sodium chloride, as indicated by zeta potential measurements, does not act as an indifferent electrolyte and affects the surface structure of apatite. However, in the case of dolomite, sodium chloride reduces the adsorption of the collector by compressing the electrical double layer. Satisfactory separation of apatite from its mixture with dolomite is achieved at pH 6.3 with dodecylamine collector In the presence of sodium chloride. 

Theory. The action of these indicators is based on the properties of colloids and can readily be explained by considering the determination of chloride using silver nitrate solution as a titrant in the presence of fluorescein as indicator. The adsorption characteristics of AgCI precipitated during titration are shown diagrammatically in Figure 1. 

Gravimetric method such as AgCl or fire assay is used. Gay-Lussac method involves the titration of Ag with NaCl and/or KBr in acid solution. The endpoint is taken as the point at which no further precipitation of silver halide is observed upon the addition of more precipitant. Fajans method is based on the precipitation of Ag with chloride or bromide ions, using an adsorption indicator to detect the endpoint. Rhodamine 6G or dichlorofluorescein is used as the adsorption indicators. Volhard method is based on the titration of Ag with potassium or sodium thiocyanate to form insoluble silver thiocyanate. This titration is... 

In an early work by Petzold and Lunkwitz [9], this efficiency of recharging of the fibres using cationic complexes of poly(diallyldimethylammonium chloride), PDADMAC, and poly(maleic acid-co-a-methylstyrene), MS-a-MeSty, was used to flocculate cellulose fibres, but the actual adsorption of the complexes was not measured. The adsorption of anionic complexes of polyethyleneimine (PEI) and CMC on fibres pretreated with a cationic PDMDAAC has also been studied by Hubbe et al. [24]. These authors found that when the charge of the complexes was decreased there was an increase in adsorption, indicative of an electrosorption process, but the authors also detected signs of nonionic interaction although they were not able to establish the molecular reason for this behaviour. 

An alternative method of end-point detection in the direct titration of halides with silver nitrate is by the use of adsorption indicators. First described by Fajans, these methods depend upon the fact that the colloidal precipitate of silver halide adsorbs ions from solution before the end-point is reached a layer of negatively charged chloride ions is adsorbed but as soon as silver ions are present in excess these are adsorbed on to the precipitate and attract the negatively charged anion of indicators of the fluores-... 

This is exemplified in the use of tartrazol as an adsorption indicator in the estimation of chlorides (p. 394). 

T artrazine, 4,5-dihydro-5 -oxo-1 -(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-1// -pyrazole-3-carboxylic acid trisodium salt was discovered by Ziegler in 1884 and is used as a dye for wool and silk. It is used as a colour additive in foods, drugs and cosmetics, and is an adsorption-elution indicator for chloride estimations in biochemistry (B-76MI40404). 

Cabon tetrachloride, n-hexane, chloroform, ACN, acetone, THF, pyridine, acetic acid, and their various mixtures were applied as mobile phases for adsorption TLC. Methanol, 1-propanol, ACN, acetone, THF, pyridine and dioxane served as organic modifiers for RP-TLC. Distilled water, buffers at various pH (solutions of and dipotassium hydrogen phosphate or potassium dihydrogen phosphate) and solutions of lithium chloride formed the aqueous phase. Carotenoids were extracted from a commercial paprika sample by acetone (lg paprika shaken with 3 ml of acetone for 30 min), the solution was spotted onto the plates. Development was carried out in a sandwich chamber in the dark and at ambient temperature. After development (15 cm for normal and 7cm for HPTLC plates) the plates were evaluated by a TLC scanner. The best separations were realized on impregnated diatomaceous earth stationary phases using water-acetone and water-THF-acetone mixtures as mobile phases. Some densitograms are shown in Fig.2.1. Calculations indicated that the selectivity of acetone and THF as organic modifiers in RP-TLC is different [14],... 

Practical considerations and implementation. Most investigations involve the use of distilled/deionised water with KNO3 as the nitrate ion source thereby avoiding any potential impact of water hardness and dissolved salts on the catalytic removal of nitrates. It has been pointed out that in the presence of anions such as S04 and bicarbonates, which may be present in tap-water at concentrations of above 90 ppm, reduced nitrate reduction rates are to be expected as a result of competitive anion adsorption. Pintar and co-workers have indicated that nitrate removal rates are reduced when using drinking water as opposed to distilled water. Chloride ion is known to reduce the rate of nitrate removal while the choice of cation as counter ion influences the rate in the order, < Na < Ca < Mg + <... 

A study has been carried out on the interactions of blood with plasticised poly(vinyl chloride) biomaterials in a tubular form. The influence of different factors such as the biomaterial, antithrombotic agent, blood condition and the nature of the application is represented when considering the blood response in the clinical utilisation of the plasticised PVC. The PVC was plasticised with di-(2-ethylhexyl)phthalate (DEHP) and tri-(2-ethylhexyl)trimellitate (TEHTM)and in-vitro and ex-vivo procedures used to study the biomaterial with respect to the selection of the plasticiser. The blood response was measured in terms of the measurement of fibrinogen adsorption capacity, thrombin-antithrombin III complex and the complement component C3a. X-ray photoelectron spectroscopy was used for surface characterisation of the polymers and the data obtained indicated that in comparison with DEHP-PVC, there is a higher reactivity... 

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