Colour intensity

The extractive and photometric procedure of 2,4-D determination in aqueous solutions with crystal violet (CV) is developed. Determination method is based on interaction dye cation with formation of hydrophobic and ionic associate, which is extracted well by toluene. The colour intensity of toluene layer proportional to concentration of coloured cations and... 

In this work hybrid method is suggested to determine anionic surfactants in waters. It is based on preconcentration of anionic surfactants as their ion associates with cationic dyes on the membrane filter and measurement of colour intensity by solid-phase spectrophotometry method. Effect of different basic dyes, nature and hydrophobicity of anionic surfactants, size of membrane filter pores, filtration rate on sensitivity of their determination was studied. Various cationic dyes, such as Methylene Blue, Crystal Violet, Malachite Green, Rhodamine 6G, Safranin T, Acridine Yellow were used as counter ions. The difference in reflection between the blank and the sample was significant when Crystal Violet or Rhodamine 6G or Acridine Yellow were used. 

Johnson has described a method for the estimation of physostigmine in the salicylate for the determination of minute amounts of the alkaloid Ellis, Plaehte and Straus have devised processes depending on (a) inhibition of serum choline-esterase by the alkaloid, or (b) measurement of the colour intensity produced by the conversion of physostigmine to rubreserine in an alkaline medium. i ... 

Discussion. Molybdenum(VI) in acid solution when treated with tin(II) chloride [best in the presence of a little iron(II) ion] is converted largely into molybdenum(V) this forms a complex with thiocyanate ion, probably largely Mo(SCN)5, which is red in colour. The latter may be extracted with solvents possessing donor oxygen atoms (3-methylbutanol is preferred). The colour depends upon the acid concentration (optimum concentration 1M) and the concentration of the thiocyanate ion (1 per cent, but colour intensity is constant in the range 2-10 per cent) it is little influenced by excess of tin(II) chloride. The molybdenum complex has maximum absorption at 465 nm. 

If the colour intensities of the two forms differ considerably the intermediate colour is attained at potential somewhat removed from Efn, but the error is unlikely to exceed 0.06 volt. For a sharp colour change at the end point, Efn should differ by about at least 0.15 volt from the standard (formal) potentials of the other systems involved in the reaction. 

Application of Beer s Law. Consider the case of two solutions of a coloured substance with concentrations c, and c2. These are placed in an instrument in which the thickness of the layers can be altered and measured easily, and which also allows a comparison of the transmitted light (e.g. a Duboscq colorimeter, Section 17.5). When the two layers have the same colour intensity ... 

D. Balancing method (Section 17.5). This method forms the basis of all colorimeters of the plunger type, e.g. in the Duboscq colorimeter. The comparison is made in two tubes, and the height of the liquid in one tube is adjusted so that when both tubes are observed vertically the colour intensities in the tubes are equal. The concentration in one of the tubes being known, that in the other may be calculated from the respective lengths of the two columns of liquid and the relation [equation (11)] ... 

This method is comparable in many respects with the method of weighing by substitution.) If Beer s Law is not valid for the solution, it is best to arrange matters so that the colour intensity of the standard lies close to that of the unknown. 

Proportionality between colour and concentration. For visual colorimeters it is important that the colour intensity should increase linearly with the concentration of the substance to be determined. This is not essential for photoelectric instruments, since a calibration curve may be constructed relating the instrumental reading of the colour with the concentration of the solution. Otherwise expressed, it is desirable that the system follows Beer s law even when photoelectric colorimeters are used. 

Discussion. When potassium iodide solution is added to a dilute sulphuric acid solution containing a small amount of bismuth a yellow to orange coloration, due to the formation of an iodobismuthate(III) ion, is produced. The colour intensity increases with iodide concentration up to about 1 per cent potassium iodide and then remains practically constant. 

Discussion. With an acidic titanium(IV) solution hydrogen peroxide produces a yellow colour with small amounts oftitanium(up to 0.5 mg ofTiOz permL), the intensity of the colour is proportional to the amount of the element present. Comparison is usually made with standard titanium(IV) sulphate solutions a method for their preparation from potassium titanyl oxalate is described below. The hydrogen peroxide solution should be about 3 percent strength (ten volume) and the final solution should contain sulphuric acid having a concentration from about 0.75 to 1.75M in order to prevent hydrolysis to a basic sulphate and to prevent condensation to metatitanic acid. The colour intensity increases slightly with rise of temperature hence the solutions to be compared should have the same temperature, preferably 20-25 °C. 

Use is made of colour changes resulting from reaction of pollutant and chemical reagents colour intensity indicates concentration of pollutant in the sample. Reaction can take place in solution or on solid supports in tubes or on paper strips, e.g. litmus or indicator paper. Quantitative assessment of colour formation can also be determined using visible spectroscopy. Instruments are calibrated... 

Ultrasound could play a dual role of creating higher interfacial area as well as facilitating the process of interfacial transport. This phenomenon seemed to be responsible for the increase in the colour intensity of the solution of Al3+-aluminon adsorption complex and could be explained as follows. 

Yolk colour plays a role in consumer acceptance, but the preferred colour varies in different countries. Yolk colour has no relation to nutrient content, flavour or freshness, but is often enhanced in conventional production systems by addition of synthetic pigments to the animal feed. In organic production, synthetic yolk pigments are prohibited and this normally results in paler yolks, but may also lead to greater variability in yolk colour intensity. In many European countries paler yolk colour is perceived by consumers as being associated with less natural production systems, an issue that clearly needs to be addressed by improved consumer information. 

In this method the sample is acidified and the inorganic carbon is removed with nitrogen. An aliquot is resampled for analyses. Buffered persulfate is added and the sample is irradiated in the ultraviolet destructor for about 9 min. The hydroxylamine is added and the sample stream passes into the dialysis system. The carbon dioxide generated diffuses through the gas-permeable silicon membrane. A weakly buffered phenolphthalein indicator solution is used as the recipent stream, and the colour intensity of this solution decreases proportionately to the change in pH caused by the absorbed carbon dioxide... 

The complexation of neomycin with copper results in the formation of a blue-coloured compound which has also been made the basis of a colorimetric determination of neomycin in pharmaceutical formulations . Maximum colour intensity was observed at a solution pH of 10. Further investigation showed the stoichiometry of the complex to be 1 1 in alkaline solution. 

The marked changes in the carbonyl IR bands accompanying the solvent variation from tetrahydrofuran to MeCN coincide with the pronounced differences in colour of the solutions. For example, the charge-transfer salt Q+ Co(CO)F is coloured intensely violet in tetrahydrofuran but imperceptibly orange in MeCN at the same concentration. The quantitative effects of such a solvatochromism are indicated by (a) the shifts in the absorption maxima and (b) the diminution in the absorbances at ACT. The concomitant bathochromic shift and hyperchromic increase in the charge-transfer bands follow the sizeable decrease in solvent polarity from acetonitrile to tetrahydrofuran as evaluated by the dielectric constants D = 37.5 and 7.6, respectively (Reichardt, 1988). The same but even more pronounced trend is apparent in passing from butyronitrile, dichloromethane to diethyl ether with D = 26, 9.1 and 4.3, respectively. The marked variation in ACT with solvent polarity parallels the behaviour of the carbonyl IR bands vide supra), and the solvatochromism is thus readily ascribed to the same displacement of the CIP equilibrium (13) and its associated charge-transfer band. As such, the reversible equilibrium between CIP and SSIP is described by (14), where the dissociation constant Kcip applies to a... 

Chemically, conversion into a vat consists in a 1 6-addition of hydrogen and recalls exactly the conversion of quinone into quinol. Like quinol, indigo white , also a dihydric phenol , is a weak add, the alkali salts of which are coloured intensely yellow. 

Bromcresol purple has been suggested as showing improved specificity for albumin and less variation in colour intensity compared with bromcresol green. The dye-albumin complex shows an absorption maximum at 603 nm and the use of a reagent buffered at pH 5.2 appreciably reduces the tendency of the complex to precipitate. 

For accurate measurements of the colour intensity of a solution, chemists use a device called a spectrophotometer. (See Figure 6.4.)... 

Because the reaction involves a colour change, you can determine the concentration of Fe(SCN) (aq) by measuring the intensity of the colour. You will find out how to do this in Investigation 7-A. For now, assume that it can be done. From the measurements of colour intensity, you can calculate the equilibrium concentration of Fe(SCN) (aq). Then, knowing the initial concentration of each solution, you can calculate the equilibrium concentration of each ion using the chemical equation. 

The colour intensity of a solution is related to the concentration of the ions and the depth of the solution. By adjusting the depth of a solution with unknown concentration until it has the same intensity as a solution with known concentration, you can determine the concentration of the unknown solution. For example, if the concentration of a solution is lower than the standard, the depth of the solution has to he greater in order to have the same colour intensity. Thus, the ratio of the concentrations of two solutions with the same colour intensity is inversely proportional to the ratio of their depths. 

You will prepare four equilibrium mixtures with different initial concentrations of Fe (aq) ions and SCN (aq) ions. You will calculate the initial concentrations of these reacting ions from the volumes and concentrations of the stock solutions used, and the total volumes of the equilibrium mixtures. Then you will determine the concentration of FelSCN) " ions in each mixture by comparing the colour intensity of the mixture with the colour intensity of a solution that has known concentration. After you find the concentration of FelSCN) " ions, you will use it to calculate the concentrations of the other two ions at equilibrium. You will substitute the three concentrations for each mixture into the equilibrium expression to determine the equilibrium constant. 

Which solution is the least concentrated Why is the colour intensity the same when you look vertically through the solutions ... 

Pour some of the solution from test tube 2 into vial 2. Look down through vials 1 and 2. Add enough solution to vial 2 to make its colour intensity about the same as the colour intensity of the solution in vial 1. Use a sheet... 

Wrap a sheet of paper around vials 1 and 2 to prevent light from entering the sides of the solutions. Looking down through the vials over a diffuse light source, adjust the volume of the standard solution in vial 1 until the colour intensity in the vials is the same. Use a medicine dropper to remove or add standard solution. Be careful not to add standard solution to vial 2. 

When the colour intensity is the same in both vials, measure and record the depth of solution in each vial as carefully as possible. 

How did the colour intensity of the solutions in test tubes 2 to 5 vary at equilibrium Explain your observation. 

The alkaloids pass through the dialysis membrane from the pH 4 buffered sulphuric acid extract donor stream into a pH 9 buffered aniline recipient stream. They are then reacted with cyanogen bromide to produce a yellow colour, the absorbance of which is measured at 460 nm after passage through a suitable delay coil to allow the full colour intensity to develop. 

---