Xylenol Orange as indicator

Iron (and nickel, if present) can be determined by adding an excess of standard EDTA to the cold solution, and then back-titrating the solution with lead nitrate solution using xylenol orange as indicator provided the solution is kept cold, chromium does not react. The solution from the back-titration is then acidified, excess of standard EDTA solution added and the solution boiled for 15 minutes when the red-violet Cr(III)-EDTA complex is produced. After cooling and buffering to pH 6, the excess EDTA is then titrated with the lead nitrate solution. 

The cobalt content may be rapidly checked by titration with standard EDTA solution in the presence of xylenol orange as indicator (see Section 10.59). 

Theory The solution of potassium alum is heated with an excess of disodium edetate to ensure complete formation of aluminium-edetate complex. Hexamine serves as a buffer thereby stabilizing the pH between 5 and 6, the ideal pH for the titration of the disodium edetate not required by the A1 with 0.05 M lead nitrate employing xylenol orange as indicator. The various reactions involved may be represented by the following equations ... 

The solubility product constant (Ksp) of EDTA was determined by adjusting the pH of an aqueous solution to a low value using nitric acid, and leaving the system to reach equilibrium overnight at room temperature. The precipitate was filtered off, dried at 105°C, and weighed to determine the amount of solubilized material. Alternatively, the precipitate was analyzed by complexometric titration, using standardized 0.05 M Zn(II) solution and xylenol orange as indicator [12]. The estimated value of the solubility product is 10 24 66 (pKsp = 24.66). 

C. (a) Explain why the change from red to blue in Reaction 13-2 occurs suddenly at the equivalence point instead of gradually throughout the entire titration, (b) EDTA buffered to pH 5 was titrated with standard Pb, with xylenol orange as indicator (Table 13-2). (i) Which is the principal species of the indicator at pH 5 (ii) What color was observed before the equivalence point (iii) What color was observed after the equivalence point (iv) What would the color change be if the titration were conducted at pH 8 instead of pH 5 ... 

Cerous nitrate, 0.0005 M, standardise approximately 0.02 M cerous nitrate by titration against standard etbylenediaminetetraacetic acid solution at pH 6 with xylenol orange as indicator. To a suitable volume of this solution (about 50 ml) add 0.2 ml of concentrated nitric acid, 0.1 g of hydroxylamine hydrochloride and sufficient water to produce 2 litres and filter. 

Pb + may be directly titrated with complexone(III) in hexamethylenetetramine medium with xylenol orange as indicator. The pH value is located about 5.6. A similar titration of Zn + can be carried out at pH about 6 with xylenol orange or methyl thymol blue as the indicator. Hexamine is then the buffer. This titration is also possible in ammonia buffer (pH about 10) in the presence of eriochrome black T. 

Weigh 2 g into a flask, add 100 ml of water, stopper the flask and shake for about five minutes. Filter into a 500-ml flask, washing the first flask and the filter with a further 100 ml of water and, to the combined filtrate and washings, add 40 ml of 0 05M EDTA and neutralise to congo red with sodium hydroxide solution. Heat on a water-bath for fifteen minutes, cool, add 1 to 2 g of hexamine and titrate the excess EDTA with 0-1M zinc solution using xylenol orange as indicator. 1 ml0-05M EDTA = 0-001349 g Al. 

Dilute 10 ml to 100 ml with water in a graduated flask. To 10 ml add 40 ml of 0-05M EDTA, 90 ml of water and 015 ml of methyl red indicator. Neutralise with N sodium hydroxide, added dropwise, warm on a water-bath for thirty minutes and cool. Add 1 ml of dilute nitric acid (this is necessary, as otherwise there is insufficient acid to produce the required buffering action). Then add 5 g of hexamine and titrate with 0 05M lead nitrate using xylenol orange as indicator. 1 ml 0 05M - 0-001349 g Al. 

Lead may be titrated directly with EDTA at a pH of about 5 or 6 using xylenol orange as indicator. Under suitable conditions the end-point is very sharp but with materials such as lead monoxide where an excess of acid must be used to bring about solution, a rather sluggish end-point is obtained. Examples of the use of EDTA for titration of lead are given in the discussion of lead salts below. 

M EDTA, using 0-2 ml of a 0-1 per cent solution of xylenol orange as indicator until the colour becomes yellow. 1 ml 0-05M = 0 01897 g C4He04Pb,3H20. 

Pipette 30 ml of 0 05M EDTA into a flask, add 1 g of hexamine and 100 ml of water and titrate with the lead nitrate solution using xylenol orange as indicator. 

A precipitation titration method has been reported where chlorpromazine hydrochloride is precipitated from solutions using excess standard Cdlj in the presence of K1 or HI, and the excess Cdl2 in the filtrate is then determined complexometrically using xylenol orange as the indicator [58]. 

The BP [3] described a similar titrimetric method for the determination of edetate disodium. Here, the titration is performed in hexamine / HC1 buffer using 0.1 M lead nitrate as the titrant and xylenol orange as the indicator. Each milliliter of 0.1 M lead nitrate solution is equivalent to 37.22 mg of Ci0Hi4N2Na2O8-2H2O. 

We determined the cation ratio by EDTA titration using Xylenol Orange as the indicator. The pH was buffered to the 5.0-6.5 range using sodium acetate/acetic acid to optimize indicator effectiveness. Each crystal was weighed and dissolved in dilute HCl from which two aliquots were taken. One was treated directly with EDTA to obtain the total metal concentration according to the reaction... 

Fluoride may be determined by precipitation as lead chlorofluoride, the precipitate being dissolved in dilute nitric acid and, after adjusting the pH to 5-6, the lead is titrated with EDTA using xylenol orange indicator.10... 

The indicator solution is prepared by dissolving 0.5 g of xylenol orange in 100 mL of water. For storage it is best kept as a solid mixture with potassium nitrate (page 316). 

Procedure Weigh accurately 1.7 g of potassium alum and dissolve it in sufficient DW in a flask. Heat the contents of flask over a water-bath for 10 minutes to allow completion of complexation and cool to ambient temperature. Now, add 1 g hexamine to act as buffer and titrate with 0.05 M lead nitrate employing 0.4 ml of xylenol orange solution as an indicator. The colour shall change from that of the indicator (yellow at the pH of the titration) to the corresponding reddish purple, the colour of the lead complex of the indicator. Each ml of 0.05 M disodium edetate is equivalent to 0.02372 g of KA1(S04)2, 12H20. 

The metal ion indicator xylenol orange (Table 12-3) is yellow at pH 6 ( max = 439 nm). The spectral changes that occur as VOz+ is added to the indicator at pH 6 are shown below. The mole ratio V02+/xylenol orange at each point is... 

The best indicator for use in acidic media from 0.1 M HN03 up to pH 5.6 is xylenol orange (XO 44). Direct determinations can be made of cadmium and cobalt (at 60 °C), copper (in the presence of phen), lead and zinc, scandium, indium, yttrium and the lanthanons, zirconium, hafnium and thorium. Many other elements that block the indicator can be determined indirectly. Consecutive titrations such as Bi (at pH 2) and Pb (at pH 5.5) can be carried out in the same solution and the colour change for the latter is particularly sharp from an intense reddish violet to lemon yellow. The extensive literature on this indicator is reviewed in several places. 2>4>76.87... 

A different vesicular photoimaging material consists of an assembly of lipid vesicles sensitized with rhodopsin. In one system the vesicles can be filled with a solution containing Co2+, and the solution outside the vesicles can be free of metal ions but contain a chelating indicator dye such as xylenol orange (101). The whole assembly can be coated, and when exposed to actinic radiation the vesicles are disrupted in exposed areas and release Co2+ ions, which are complexed by the dye indicator, thereby forming an image.253... 

Figure 18 (a) Molecular structures of Cp Rh complex 51 with indicators such as gallocyanine 52, xylenol orange 53, and calcein... 

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