Thymolphthalein solution

Standardization of 0.1 M Ethanolic Sodium Hydroxide Solution Vs Dissolve 0.2 g of benzoic acid in a mixture of 10 ml of ethanol (96%) and 2 ml of water and titrate with the ethanolic sodium hydroxide solution using 0.2 ml of thymolphthalein solution (a 0.1 % w/v solution of thymolphthalein in ethanol (96%) as indicator. Each ml of 0.1 M ethanolic sodium hydroxide Vs is equivalent to 12.21 mg of C7H602. 

Formalin (formaldehyde solution, 37%), sodium sulfite, sodium hydrogen sulfite, ethylencdiamine tetraacetate (EDTA), thymolphthalein solution, p-nitrophenol, phenolplulialein, elhaiiol. 

Thymolphthalein complexone (thymolphthalexone). This is thymolphthalein di(methyliminediacetic acid) it contains a stable lactone ring and reacts only in an alkaline medium. The indicator may be used for the titration of calcium the colour change is from blue to colourless (or a slight pink). Manganese and also nickel may be determined by adding an excess of standard EDTA solution,... 

Cherry and Crandall in 1932 (86) used olive oil as substrate with gum acacia as the emufsTfier. This method has served as the basis for a number of modifications that increased the stability of the emulsion, decreased incubation time and gave better precision. When a serum sample is incubated with a stabilized olive oil emulsion, lipase acts at the interface of substrate and water to hydrolyze olive oil into fatty acid plus diglycerides, and to a small extent to monoglycerides and glycerol. The bile salt sodium deoxycholate activates the reaction. These methods measure the liberated fatty acids by titration with a standardized NaOH solution. An indicator such as phenolphatalein, thymolphthalein or methyl red or a pH meter are used to detect the end point. 

Whether for a class demonstration, a practical joke, or perhaps a clandestine activity, disappearing ink is a fascinating substance. What is the secret to its action One formulation of disappearing ink contains a common acid-base indicator, that is, a substance that by its color shows the acid or basic nature of a solution. One acid-base indicator that shifts from a colorless hue under acidic conditions to a deep blue color in alkaline solutions is thymolphthalein. If the indicator starts off in a basic solution, perhaps containing sodium hydroxide, the typical blue color of an ink is perceived. How does the ink color disappear This behavior is dependent upon the contact of the ink with air. Over time, carbon dioxide in the air combines with the sodium hydroxide in the ink solution to form a less basic substance, sodium carbonate. The carbon dioxide also combines with water in the ink to form carbonic acid. The indicator solution responds to the production of acid and returns to its colorless acid form. A white residue (sodium carbonate) remains as the ink dries. 

Disappearing ink can be prepared by first dissolving solid thymolphthalein in ethanol, adding water, and then adjusting the pH with sodium hydroxide solution J2 The deep blue color of the basic form of the indicator is readily apparent. Applying the ink to paper increases its exposure to carbon dioxide in air. Two chemical... 

Thymolphthalein assumes its basic color in a solution with pH = 11.62 the solution is blue. 

These constants determine the titration exponents pH and the best indicators for the successive hydrions. The acid can be titrated as dibasic, using methyl yellow, methyl orange or bromophenol blue, and as tetrabasic using phenolphthalein, thymolphthalein or thymol blue in the presence of a moderate excess of soluble barium salt. The values of pH in the partly neutralised acid were corrected for the salt error, and the constants Kz and jfiT4 which prevail in solutions of low concentration were thus deduced —6... 

Thymolphthalein A white to slightly yellow, crystalline powder. Insoluble in water soluble in alcohol and in solutions of alkali hydroxides. Transition interval from pH 9.3 (colorless) to 10.5 (blue). 

Universal Indicators.—Since the pH range over which a given indicator can be employed is limited, it is always necessary, as mentioned above, to carry out preliminary measurements with an unknown solution in order to find the approximate pH with this information available the most suitable indicator can be chosen. For the purpose of making these preliminary observations the so-called universal indicators have been found useful they consist of mixtures of four or five indicators, suitably chosen so that they do not interfere with each other to any extent, which show a series of color changes over a range of pH from about 3 to 11. A convenient and simple form of universal indicator can be prepared by mixing equal volumes of 0.1 per cent solutions of methyl red, a-naphtholphthalein, thymolphthalein, phenolphthalein and brom-thymol blue the colors at different pH values are given below. 

Formaldehyde-water solution. Mix 50 ml of 38% formaldehyde with 50 ml of distd w in a 400-ml beaker, add 4 drops of 1% phenolphthalein or thymolphthalein indicator (0.8g per 100ml ethanol) and neutralize with carbonate-free 0.5N NaOH soln dropwise to a pink color (pH 8.6) on glass-calomel electrode system Standard sodium hydroxide, 0.5N. Dissolve 20g of carbonate-free NaOH in 500ml CO2-free water, add enough Ba chloride to more than 2 liters distd w to precipitate carbonate present, let the Ba carbonate settle, and filter into a 1 liter volumetric flask. Standardize the NaOH soln by adding it. from a buret into a soln of 2 g of potassium acid phthalate (weighed accurat ely on an analytical balance), and four drops of phenolphthalein indicator in 75—100ml COa-free water contained in a 150-ml beaker until the first appearance of a pink end point... 

The contents of the flask arc then back titrated with 0.5 N HCl using thymolphthalein indicator solution / ml). 

Dilute the initial formaldehyde solution to around 5 g F for testing. Pipette 50 ml of 1 M sodium sulphite (Na SO,) into a 250 ml beaker. Add 2-3 drops of thymolphthalein indicator. Pipette 10 ml of the formaldehyde testing solution into the beaker. A blue colour appears. Titrate the solution with a 0.05 N standard sulphuric acid until the blue colour just disappears. Record the volume (ml) of the standard sulphuric acid used. Calculate the concentration of the fonnaldehyde testing solution ... 

Thymolphthalein. The structure of this indicator is like that of phenolphthalein, with the exception that the phenol groups are replaced by two thymol groups. It melts at 253 . A convenient stock solution may contain 0.1% of the indicator in an 80% alcohol solution. Its color change interval lies between pH 9.3 and 10.5, the color changing from colorless to blue. 

The colorless form is very insoluble in water. Consequently, if the indicator is added to a solution with a pH of 10, a fading of the blue color will be perceptible after a short time of standing. The separation of the colorless form of the indicator will thus displace the customary equilibrium towards the acid side. The more indicator employed and the longer one waits for the appearance of this phenomenon, the more pronounced will be the effect. For this reason thymolphthalein is not very satisfactory for use in the colorimetric determination of pH. The indicator is suitable, however, for titrimetric purposes. 

The phthaleins too assume a color in strong acid solutions. In aqueous solution, these compounds exist almost entirely as lactones, although here too we must assume that a small fraction is present in the quinoid form. The acid form, however, does not become visible until the acidity attained is much greater than that required by the corresponding sulfonephthalein. We find for example that thymolphthalein is still colorless in 6 N hydrochloric acid, but pale rose in 9 N and dark violet in concentrated hydrochloric or sulfuric acid. Phenolphthalein is weakly rose-colored in 9 N and 12 N hydrochloric acid, but orange-brown in concentrated sulfuric acid, a-naphtholphthalein also is colorless... 

J. Moir prepared a universal indicator of a wider range by using a mixture of methyl red, a-naphtholphthalein and phenolphthalein. F. H. Carr added bromthymol blue and thymolphthalein to this mixture. The relative amounts of the various indicators were not reported by these authors. A useful universal indicator may be prepared by mixing equal volumes of 0.1% solutions of the five indicators named above. This indicator solution is red at a pH of 4,0, orange-red at 5, yellow at 6, green-yellow at 7, green at 8, blue-green at 9, blue-violet at 10, and red-violet at 11. 

Thymolphthalein. This study was performed exactly as was the preceding, so that only data need be presented. The solubility is much less than that of phenolphthalein, since turbidity resulted from the addition of 12.5 c.c. of a 0.1% solution per liter. The solubility of the indicator is thus 1.25 X 10 g. per liter. It was shown in addition that [I miti.Il = 1 X 10 g. per liter. 

It is clear from these tables that the figures have no theoretical significance, because actually thymolphthalein and phenolphthal-ein are much more sensitive to hydroxyl ions than is indicated above. The true sensitivity can be determined only by using buffer solutions. It should be remembered, furthermore, that alcohol not only changes the color intensity but the color as well. Phenolphthalein in aqueous alkaline solution is cherry red, assumes a violet tint in dilute alcoholic solution, and is bluish violet in concentrated alcohol. Furthermore the color intensity of an alkaline phenolphthalein solution is much less in alcohol than in water. ... 

A sufficient number of comparison solutions must be prepared so that the color of the liquid being investigated always falls between two comparison solutions. Furthermore, exactly the same volume of the same indicator solution must he added to the comparison and unknown solutions. The concentration of one-color indicators is of very great importance. In the case of two-color indicators, concentration plays a minor role since the relationship between the concentrations of the acid and alkaline form determines the color. Here too, however, it is advisable to add the indicator from a small pipette rather than a dropper. Duplicate colorimetric measurements with phenolphthalein (also thymolphthalein, p-nitrophenol, nitramine, etc.) may differ appreciably unless the specified quantity of indicator solution is measured out accurately. 

Thymolphthalein is not especially suitable for the determination of pH. The acid form is insoluble in water and fading of the color is nearly always observed. When 0.1 c.c. of a 0.1% indicator solution is added to 10 c.c. of a carbonate buffer of pH 10, there appears a light blue color which fades rapidly on standing, due to the flocculation of the acid form. Indicator must be added simultaneously to the buffer and unknown solution and the colors compared immediately if thymolphthalein is used. Even so, results are not always reliable. 

Salt Corr ection op Thymolphthalein, Alizarine Yellow, and Salicyl Yellow in an Equimolecular Mixture op Sodium Carbonate AND Sodium Bicarbonate (Compared with Sodium Carbonate-Borate Buffer Solutions)... 

Finely divided particles in suspension can also interfere with colorimetric mea.surements if one of the indicator forms happens to be preferentially adsorbed. Lanthanum hydroxide is a very striking example of such interference. This compound is a strong base which is very slightly soluble in water. A saturated solution in water at 25° has a pH of 9.0. If the pH of a suspension (turbid solution) of the solid hydroxide is measured with thymol-phthalein, the result obtained is 10.5. The suspension is colored a dark blue, although thymolphthalein is colorless at pH 9.0. The precipitate settles after a time, leaving a colorless supernatant solution although the solid itself is dark blue. Because of the strong basic properties of solid lanthanum hydroxide, it forms on its surface a salt with the indicator acid. In other words, the adsorption of the colored indicator anion predominates, and the presence of the solid phase favors a displacement of the indicator equilibrium towards the alkaline form. Phenol-... 

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