Phenolphthalein 294, cover

The pH range for acids with Ka > 10-5 is 7-10.5 for weaker acids (Ka > 10-6) the range is reduced (8-10). The pH range 8-10.5 will cover most of the examples likely to be encountered this permits the use of thymol blue, thymolphthalein, or phenolphthalein. 

Desoxycholic Acid, Fatty Acids, Cholesterol.—The first alcoholic filtrate obtained during the crystallisation of the cholic acid (see above) is made strongly alkaline to phenolphthalein paper with 2 N-sodium hydroxide solution and concentrated to a syrupy consistency in a porcelain basin on the water bath. The syrup is taken up in 250 c.c. of water, transferred to a separating funnel, cooled, covered... 

Procedure (neutralizing value). At the same time as weighing the sample for moisture determination, weigh 0.5 g (AOAC 1 g, but 0.5 g for CaO or Ca(OH)2), or x g, of the prepared sample to the nearest 0.001 g, and transfer to a 300-ml (AOAC 250-ml) conical flask. Add 50 ml of 0.5 M hydrochloric acid, cover the flask with a watch glass and boil the contents gently for 5 min. Cool the mixture to room temperature, add 2 or 3 drops of the phenolphthalein indicator and titrate with 0.5 M sodium hydroxide solution to the end point of the indicator. 

Procedure for Ammonium Nitrate. Transfer a 25-ml aliquot from the bottle of step 6 to 100 ml of the neutralized form aldehyde-water soln in a 400-ml beaker, add 4 drops of 1% phenolphthalein (or thymolphthalein) indicator and titrate to a pink color with. 0.5N NaOH. Add 2ml of NaOH in excess, cover the beaker, and let stand for 5 mins. Back-titrate with 0.1N HCl to pH 8.5 (glass-calomel electrode system)... 

The I2O7 content of the periodates described is determined as follows The weighed sample is covered with 20 ml. of water, and 5 to 10 drops of 6N HC1 is added to hasten solution. No chlorine is liberated from the acid of this concentration. The solution is diluted to 100 ml., made just alkaline to phenolphthalein paper with borax, buffered with borax and boric acid (Muller and Wegelin Z. anal. Chem., 52, 755-759 (1913), and an excess of potassium iodide is added. Under these conditions, the periodate is reduced to iodate. The liberated iodine is titrated with 0.1N arsenite. 

Assay Transfer about 400 mg of sample, accurately weighed, into a 250-mL Erlenmeyer flask, add 20 mL of water and 40 mL of alcohol, cover with a watch glass, heat gently on a steam bath until dissolved, and cool. Add 5 drops of phenolphthalein TS, and using a 10-mL microburet, titrate with 0.1 N sodium hydroxide to the first pink color that persists for 15 s. Perform a blank determination (see General Provisions) and make any necessary correction. Each milliliter of 0.1 N sodium hydroxide is equivalent to 40.86 mg of... 

Sample Preparation Transfer 10.0 g of sample into a 100-mL beaker, dissolve in 15 mL of water, add 2 drops of phenolphthalein TS, and while constantly stirring, slowly neutralize with 1 2 hydrochloric acid. Add 1 mLof 1 5 sulfuric acid and 1 mL of a 1 25 solution of potassium permanganate, cover the beaker with a watch glass, boil for a few seconds, and cool. 

Procedure Transfer an accurately measured volume of sample, equivalent to about 25 mg of diacetyl, into a suitable flask. Add 3 drops of phenolphthalein TS, and neutralize the acidity by titrating with 0.05 N sodium hydroxide to a faint pink endpoint. Add 0.25 mL of 30% hydrogen peroxide solution and 3 drops of 0.01% Osmic Acid. Mix, cover the flask, and allow it to stand in an incubator held at about 38° for not less than 4 h. Cool to room temperature, and titrate with 0.05 N sodium hydroxide to a faint pink endpoint. Each milliliter of 0.05 N sodium hydroxide is equivalent to 8.6 mg of diacetyl. 

Assay Transfer about 1 g of the sample, accurately weighed, into a suitable pressure bottle, add 25.0 mL of 1 A potassium hydroxide and 15 mL of isopropanol, stopper the bottle, and wrap securely in a canvas bag. Place in a water bath maintained at 98° + 2°, and heat for 1 h, allowing the water in the bath to just cover the liquid in the bottle. Remove the bottle from the bath, cool in air to room temperature, then loosen the wrapper, uncap the bottle to release any pressure, and remove the wrapper. Add 6 to 8 drops of phenolphthalein TS, and titrate the excess alkali with 0.5 N sulfuric acid just to the disappearance of the pink color. Perform a blank determination (see General Provisions). Each mL of 0.5 N sulfuric acid is equivalent to 36.37 mg of C9H14O6. 

Ferroxyl.—An effective method of showing that differences of potential exist between different parts of a piece of iron consists in utilising the ferroxyl indicator devised jointly by Cushman1 and Walker.2 A 1 5 per cent, solution of agar-agar jelly is prepared, a few drops of phenolphthalein added, and the whole rendered perfectly neutral whilst hot by titration either with alkali or acid as occasion requires. A small quantity of potassium ferricyanide solution is now added, and the solution poured into a shallow dish to cool. A clean sample of iron is placed on the solidified jelly and covered with a layer of warm solution, and the whole allowed to cool. After a few hours some very beautiful colour effects will have developed, and may be preserved for several months by keeping the surface of the agar covered with alcohol. 

We have already discussed the properties of human erythrocytic acid phosphatase (Section 3.3), and we pointed out that, like acid phosphate in other tissues, it may exist in several isoenzymatic forms. In 1963, Hopkinson et al. (H13) subjected hemolysates of human red cells from an English population to horizontal starch-gel electrophoresis for 17 hours at 5°C. The gels were then sliced horizontally, covered with 0.05 M phenolphthalein sodium diphosphate at pH 6.0, and allowed to incubate for 3 hours at 37°C. Five different electrophoretic patterns of acid phosphatase activity could be distinguished in different individuals. Shortly thereafter Lai and his associates (L2) confirmed these findings and discovered an additional sixth pattern which had been predicted by Hopkinson et al. (H13). The distribution of these patterns in various types of population was assiduously pursued within the next several years, and several new ones were discovered in Negro populations (G3, K2). 

Filter the supernatant solution through a No. 4 glass frit covered by a paper filter. Titrate exactly 20 ml of the clear or opalescent filtrate against 0.1 N sodium hydroxide solution, using phenolphthalein as indicator (titre in ml = t). 

Figure 8.4 illustrates the colors and transition ranges of some commonly used indicators. The range may be somewhat less in some cases, depending on the colors some colors are easier to see than others. The transition is easier to see if one form of the indicator is colorless. For this reason, phenolphthalein is usually used as an indicator for strong acid-base titrations when applicable (see Figure 8.1, titration of 0.1 M HCl). In dilute solutions, however, phenolphthalein falls outside the steep portion of the titration curve (Figure 8.2), and an indicator such as bro-mothymol blue must be used. A similar situation applies to the titration of NaOH with HCl (Figure 8.3). A more complete list of indicators is given on the inside back cover.

Carbonation depth is easily measured by exposing fresh concrete and spraying it with phenolphthalein indicator solution. The carbonation depth must then be related to the cover (the average and its variation) so that the extent to which carbonation has reached the rebar can be estimated, and the future carbonation rate estimated. 

Figure 4.9 Phenolphthalein applied to a concrete window mullion showing approximately 10 mm carbonation depth (clear area at surface) and an uncorroded bar in uncarbonated concrete with a cover depth of approximately 40 mm.

Carbonation is easy to detect and measure. A pH indicator, usually phenolphthalein in a solution of water and alcohol, will detect the change in pH across a freshly exposed concrete face. Phenolphthalein changes from colourless of low pH (carbonated zone) to pink at high pH (uncarbonated concrete). Measurements can be taken on concrete cores, fragments and down drilled holes. Care must be taken to prevent dust or water from contaminating the surface, is cheap and simple. Figure 3.1 shows a typical carbonation front in concrete with the pH of the concrete before and after carbonation, the pH threshold of corrosion for steel and the pH change of phenolphthalein taken from Parrott (1987). The measurement of the carbonation front is covered in Section 4.6. 

Figure 4.8 Carbonation test on a reinforced concrete mullion. In this case the carbonation had only penetrated about 5mm on an element with a 25 mm cover. Phenolphthalein solution sprayed on to the freshly exposed concrete shows pink in the alkaline areas (the darker central area around the rebar), and remains clear in the carbonated areas near the surface.

Fig. 4. The shape of a phenolphthalein spot at the expanding surface of water covered with the phospholipid monolayer.

The testing of concrete specimens with respect to the level of carbonation is carried ont by applying a phenolphthalein solution to a freshly fractured or sawn snrface. Noncarbonated areas become red while carbonated areas remain grey. The rate of carbonation in ordinary concrete elements exposed to the atmosphere is schematically shown in Figure 11.25. It is assumed that the depth of cover d of steel-reinforcement should be bigger than the depth of carbonation estimated after 100 years to ensure safety of reinforcement (CEB 1992). In normal conditions, half of that depth can be reached within 15 years. A simplified formula proposed for the carbonation rate is d = 10 V t, here d is in mm and t in years b is a numerical coefficient that characterizes the quality of concrete, for example, for a very good quality concrete b = 0.15. Carbonation is usually deeper on those sides of a structure that are exposed to sunshine because the process of conversion into calcium carbonate CaCOj by carbon dioxide CO2 is quicker in frequently variable hydro-thermal conditions. 

Equivalent weights for PFSI ionomers immediately following precipitation from the reaction medium and for membranes formed as described in section 22.5 were measured by acid-base titration. In brief, the procedure is as follows. A known amount of dried polymer (in a typical measurement, approximately 0.0670 g of polymer) and 0.10 g of NaCl were dissolved in 30 mL of deionized water, and the resulting solution was refluxed in a 150-mL conical-shaped flask at 80°C overnight with constant stirring. The flask was covered with a latex balloon and then filled with nitrogen gas through a septum. The polymer swelled up in water. A few drops of phenolphthalein were added to the solution, which was then titrated with a 0.0100 M... 

Reinforcement cover. The time taken for a carbonation front to advance depends on the depth of the concrete cover. If the cover is thick enough, carbon would not reach at depths to depassivate steel. Phenolphthalein solution can be used to check depth of carbonation, by fracturing (not drilling) at a test location. A pink color indicates satisfactory concrete. 

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