Phenol phthalein alkalinity

Green originated the important technical ingrain process of developing a dye on a fabric, and worked on sulphur and stilbene dyes, aniline black, oxonium compounds, and sulphanilamide. Green and A. G. Perkin criticised Ostwald s theory of indicators and explained the red colour of alkaline phenol-phthalein as due to a quinonoid form of the undissociated molecule. 

C) Phenacyl and p-Bromophenacyl esters. Ammonium salts in aqueous-ethanolic solution do not however usually condense satisfactorily with phenacyl and />-bromophenacyl bromide. The aqueous solution of the ammonium salt should therefore be boiled with a slight excess of sodium hydroxide to remove ammonia, and the solution then cooled, treated with hydrochloric acid until just alkaline to phenol-phthalein, and then evaporated to dryness. The sodium salt is then treated as described (p. 349) to give the ester. Filter the ester, and wash with water to remove senium halide before recrystallisation. 

Completion of the run, after 30-40 hours, is indicated when a few drops of the solution show an alkaline reaction to phenol-phthalein. No harm is done if the electrolysis is carried a few hours beyond this point however, after excessively long periods, formation of polymeric material lowers the yield and renders purification of the product rather troublesome. 

See Carboxylic acids, Section 9.6.15, p. 1264.) If the substance is the free sul-phonic acid, dissolve 0.5 g of it in 5-10 ml of water, add a drop or two of phenol-phthalein indicator and neutralise with c. m sodium hydroxide solution. Then add 2-3 drops of 0.1 m hydrochloric acid to ensure that the solution is almost neutral (pale pink colour) under alkaline conditions the reagent tends to decompose to produce the evil-smelling phenylmethanethiol. 

Then the vessel is charged with 1000-2000 1. of water and 100 kg of sodium carbonate and the whole is heated with live steam until the nitronaphthalene becomes molten. This requires about 2 hr. The water should remain alkaline towards phenol-phthalein. The contents of the vessel are pumped to one of three washing tanks. The tank are made of sheet iron and equipped with a steam heater and with a stirrer (40 r. p. m). After 2 hr of agitation the lower layer (molten nitronaphthalene) is pumped into the next tank charged with a solution of 50 kg of sodium carbonate in 3000 1. of water and heated up to 85-95°C. 

Estimation of Atmospheric Carbon Dioxide.—A convenient method is that of Pettenkofer,4 which consists in introducing a standard solution of barium hydroxide into a large bottle containing several litres of the air to be examined. The bottle is shaken from time to time to keep the sides moistened wit-h the solution, and after 5 or 6 hours the absorption of carbon dioxide may be regarded as complete. The baryta solution is decanted into a small stoppered bottle and allowed to stand until any suspended barium carbonate has settled. A portion of the clear liquid is then removed and titrated with dilute sulphuric acid, using phenol-phthalein as indicator. The diminution in alkalinity due to combination with carbonic acid is thus measured, and from the data obtained the percentage of carbon dioxide m the atmosphere may easily be calculated. 

The aq. soln. of trisodium phosphate reacts alkaline to methyl orange, phenol-phthalein, and litmus and neutral to Pbrrier s blue. The aq. soln. of trirubidium and tricaesium phosphates also react alkaline. J. Shields, J. M, van Bemmelen, and A. Kossel found that in aq, soln., trisodium phosphate is almost completely hydrolyzed by water into disodium hydrogen phosphate and sodium hydroxide. E, Salm calculated that the degree of hydrolysis is about 23 per cent, of the sodium or 70 per cent, of theP04 E. Blanc that 34 1 per cent, of a0 012W-soln. 

The acid crystallises from water in colourless, glistening plates, unmelted below 320° C., soluble in alcohol, sparingly soluble in cold water, and insoluble in ether or chloroform. It forms a salt neutral to phenol-phthalein with two equivalents of alkali. Mien the acid is reduced by red phosphorus and hydriodic acid and the solution made alkaline and boiled with phosphorous acid, o-arsenobenaoic acid is formed. When the acid, ill aqueous solution, is reduced with sulphur dioxide and a little hydriodic acid at 60° C., the corresponding oxide is formed. This crystallises from water, melts at 89° C., resolidifies at about 140° C., and remelts at 225° to 281° C. Heating with alkali at 100° C. for five hours hydrolyses the oxide to benzoic acid and arsenious oxide about 15 per cent, is converted into monosodium dicarboxydiphenylarsenite. 

Acetone should be colourless and completely miscible with water. Its specific gravity should not exceed 0 800 at 15 It should give no turbidity on mixing with twenty times its volume of carbon disulphide, and no residue on evaporation. It should be free from acidity, except for traces of dissolved carbon dioxide (approximately o oi per cent,). To test acidity the acetone is boiled to remove carbon dioxide, diluted with an equal volume of water (free from carbon dioxide) and titrated with alkali, using phenol phthalein as indicator. Alkalinity should be absent, as it indicates the presence of amines it is tested for by diluting... 

The screen was displaced until the color in the field of vision was equal to that in the glass cylinder. Previous calibration of the scale with buffer solutions of known hydrogen exponent permitted the pH value to be read directly. This arrangement is very useful for determining pH of water at the location where the sample is collected, since no auxiliary instruments are required. It is evident that this instrument may be used also with other indicators, such as methyl red, methyl orange, etc. Phenol-phthalein may not be used because of the instability of its alkaline solutions. Physiological solutions, such as urine, may be examined rapidly with this instrument. 

Indicator papers frequently aid in the identification of chemicals. Strong mineral acids are acid towards methyl violet or thymol blue papers, moderately strong acids react acid towards Congo paper, and very weak acids are acid towards htmus and azolitmin paper. Strong bases show an alkaline reaction with turmeric or tropeolin 0 paper, medium strong bases with phenol-phthalein, and very weak bases with litmus or azolitmin paper. These papers are not recommended for use in quantitative analysis. ... 

Alkalinity is a measure of the acid-neutralizing capacity of the solution. It is measured by titrating the solution to pH 8.3 to determine phenol-phthalein alkalinity and to a pH near 4.5 (see Greenberg et al. (1992) for exact values) to determine total alkalinity. Note that most values reported as alkalinity are total alkalinity. Alkalinity is also reported as mg CaCOs/L equivalent, which can be interpreted as the equivalent amount of calcite needed to consume the amount of acid titrated. Because bicarbonate is usually the predominate anion in most non-marine surface waters and shallow groundwater, total alkalinity values are sometimes interpreted as a reflection of the bicarbonate concentration of the solution. This interpretation should be applied with caution because several other kinds of anions, including hydroxide, organic acids, phosphates, silicates, carbonate, and borate, contribute to the measured alkalinity. 

About 2 grammes of the sample are dissolved in 50 c.c. distilled water, and titrated with N/1 sulphuric acid, using phenol-phthalein as indicator, the alkalinity so obtained representing all the caustic alkali and one-half the carbonate, which latter is converted into bicarbonate. One c.c. N/1 acid 0 031 gramme Na. O or 0 040 gramme NaOH and 0 047 gramme KgO, or 0 056 gramme KOH. 

About 7-8 grammes of the sample are dissolved in water, and made up to 100 c.c., and the total alkalinity determined by titrating 20 c.c. with N/1 acid, using methyl orange as indicator. To another 20 c.c. is added barium chloride solution (10 per cent.) until it ceases to give a precipitate, the precipitate allowed to settle, and the clear supernatant liquid decanted off, the precipitate transferred to a filter paper and well washed, and the filtrate titrated with N/1 acid, using phenol-phthalein as indicator. The second titration gives the amount of caustic alkali present, and the difference between the two the proportion of carbonate. 

Free Alkali,—Some analysts determine the alkalinity to phenol-phthalein of the alcoholic soap solution without filtering, and express it as free alkali (caustic, carbonates, or any salt having an alkaline reaction). 

The B,P, method of estimation is by direct titration in ethanol phenol-phthalein or phenol red may be used as indicator, the colour change being quite sharp in the presence of ethanol, phenolphthalein being less sensitive. 1 ml 0 5N NaOH = 0 06106 g. Benzoic acid may also be titrated in a non-aqueous medium such as dimethylformamide, an alkaline methoxide or tetrabutylammonium hydroxide being used as titrant (see p. 793). 

Pipette 50 ml of the supernatant liquid into a 250-ml separator and extract with three portions, each of 30 ml, of light petroleum (b.p. 40° to 60°). Combine the extracts and wash with successive portions, each of 50 ml, of water until the washings are no longer alkaline to phenol-phthalein solution. Evaporate the extract to dryness under nitrogen. 

Dissolve 5-20 g of well-mixed sample in 100 mL neutralized isopropanol. Add phenol-phthalein indicator and titrate with 0.1 M NaOH solution. If the sample is already alkaline, titrate instead with 0.2 M HCl solution. Calculations ... 

Phthalein test. Many phenols yield phthaleins, which give characteristic colorations in alkaline solution, when fused with phthalic anhydride and a little concentrated sulphuric acid. Place in a dry test tube 0.5 g of the compound and an equal bulk of pure phthalic anhydride, mix well together and add 1 drop of concentrated sulphuric acid. Stand the tube for 3-4 minutes in a small beaker of Silicone oil (or paraffin oil) previously heated to 160 °C. Remove from the bath, allow to cool, add 4 ml of 5 per cent sodium hydroxide solution and stir until the fused mass has dissolved. Dilute with an equal volume of water, filter and examine the colour of the filtrate against a white background if the solution exhibits a fluorescence, observe the colour against a black background. 

This body is obtained by action of phenol on phthalic anhydride in presence of strong sulphuric acid. The free phthalein forms colourless crystals, melting at about 350° it dissolves in alkalies with a red colour, and is precipitated by acids as a white precipitate. The alkaline solution is decolorised by excess of alkali. On melting with caustic potash, it yields benzoic acid and dioxy-benzophenone. On account of the change in colour occasioned by free alkalies (not carbonate or ammonia), phcnolphthalein is useful as an indicator in titration. 

The Phthaleins. All phthaleins are rather insoluble in water but very soluble in alcohol. Most of them are colorless in acid medium (lactone form), while the alkaline form is colored (red, violet, blue, green) and possesses the quinone phenolate structure. In strongly alkaline medium the color gradually fades due to the transformation of the quinone phenolate into the colorless carbi-nol form. These structural changes will be discussed in detail in Chapter Seven. The velocity with which the colors of various phthaleins fade in alkaline medium has been measured by A. Thiel and coworkers, and the velocity constants determined. 

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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