Alkali titration

This method was described by Kurosaki et al. [28]. Their account lacks 

Weigh a sample containing about 7.5 g of mixed mono- and diester in the free acid form. Dissolve in 100 ml 65% ethanol, transfer to a 250 ml volumetric flask, dilute to volume with the same solvent and mix. 

Titrate a 100 ml portion potentiometrically with 0.5 M sodium or potassium hydroxide through two end-points. 

Titrate a second 100 ml portion to the first of these end-points. Add excess silver nitrate (amount not specified 10 ml of a 10% solution should be sufficient) and titrate through another end point at about pH 6. 

All the hydrogen ions replaced by silver ions are titrated. 

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Textbooks of analytieal ehemistry should be eonsulted for further details eoneeming the ionization of weak aeids and bases and the theory of indieators, buffer solutions, and aeid-alkali titrations. " ... 

Determination of Carboxylic Group Terminals. The carboxylic group terminals were determined by alkali titration (12.). After 200 mg of the sample was dissolved in T.5 ml of benzyl alcohol in a nitrogen atmosphere at 110 °C, the solution was titrated with 0.05N potasL- Vum hydroxide using phenolphthalein as an indicator. A blank test was carried out by the same method but omitting the sample. 

By providing the computer with starting estimates of the values and the data for [M]totai, [L]totai, and pH at each titration point, a non-linear curve fitting procedure—such as the method of Newton-Raphson—results in the minimization of the least squares function R, which is the sum of the squares of the difference between the experimental amount of alkali titrated and the calculated amount for each experimental point. 

About 2 grams of the oil are weighed in a 100 c.c. flask and treated with 10 or 20 c.c. of N/2-alcoholic potash (usually 10 c.c. suffice, 20 c.c. being used only in cases where 10 c.c. have been shown to be insufficient). The flask is closed with a cork traversed by a glass tube about a metre long or by a small upright bulb condenser, and is then heated for half an hour on a water-bath. After cooling, about 50 c.c. of water and a few drops of alcoholic phenolphthalein solution are added and the excess of alkali titrated with N/2-sulphuric acid. 

Total alkali Titratable alkali Active alkali Effective alkali... 

Cholinesterase Activity. Cholinesterase activity was assayed by automatic, continuous, alkali titration of acid released from the substrate, a method previously utilized by Wilson (12), Main and Dauterman (6), Shellenberger et al. (8), and others. 

Recently, Hiller and Pacsu have shown that accurate results may be obtained in the absence of sodium chloride by a direct alkali titration of the carboxyl groups in purified cotton. The carboxyl group content found was 0.02%, but after oxidation with potassium permanganate solution, 0.126% was found. From these data it may be seen that both carboxyl and aldehydic groups are present in the original cellulosic... 

Halogen in organosilicon compounds may be either directly linked to silicon or may be part of a substituent group. Total halogen is usually determined by alkali fusion methods. Halogen attached directly to silicon is easily hydrolysable by aqueous alcohols and the halogen acid so produced can be estimated by direct alkali titration or by indirect procedures. 

The difference between the alkali titrations in the two cases corresponds to the ester formed and hence to the original anhydride. Free-acid impurities are equal in the two cases and cancel out in the difference. In principle, this method should be applicable to sulphonyl halides and anhydrides but no example could be found in the literature. 

Modern analytical instrumentation has been used in the last 23 years for determining commercially important characteristics of soluble silicates, and the nature of silicate species in silicate glasses and solutions. The classical wet methods for assay of silicate solutions are alkali titration and gravimetric determination of silica, which can also be determined, with lesser precision, by the alkali fluosilicate method. 

Silicate to soda ratios can also be determined rapidly for quality control purposes by an alkali titration and a measurement of either specific gravity or refractive index and viscosity which are correlated to Si02/Na20 ratios using control charts. The control charts are based on samples previously analyzed by the precise gravimetric method. The specific gravity method is more commonly used in commercial practice,... 

Gravimetric silica jfO.05% Fluosilicate reaction 0.3% Alkali Titration J O.1%... 

However, in the commercial world the ultimate in precision is often not needed to satisfy the situational analytical requirements. Because the gravimetric procedure involves many time consuming steps, the fluosilicate reaction is generally preferable as the usual silica wet chemical assay method. It is not as precise as a normal alkali titration because of the difficulty of observing the end point. 

Approximately 5g of a polyol are added to 150g of OTm sodium hydroxide at 100°C. Samples of this mixture are withdrawn, weighed and quenched with water, and the remaining alkali titrated with hydrochloric acid using phenolphthalein as indicator. A graph of NaOH content versus hydrolysis time can then be drawn for comparison purposes. 

The use of an indicator in an acid-alkali titration is referred to in a monograph published in 1767 by William Lewis entitled Experiments and Observations on American Potashes with an Easy Method of determining their respective Qualities. He determined the point of saturation of the alkali by an acid by the change of colour produced in certain vegetable juices, or on a paper stained with them. Lewis advocated that the quantities of both solutions should be determined by weight. 

It has been my experience that for research purposes, in addition to the atomic absorption method for total silica, the alkali titration of silica as SiF is most useful for concentrations greater than 0.1%, and the yellow and blue silicomolybdate methods for concentrations down to 1 and 0.1 ppm, respectively. 

Her has carried out a hitherto unpublished investigation of the rates at which extremely small particles of colloidal silica depolymerize to monomer both directly in the molybdic acid reagent and in dilute alkali in which the monomer is determined on separate samples by reaction with molybdic acid. The size of the particles was estimated from the specific surface area, which was determined by the Sears alkali titration method corrected for monomer. The measurements were made as the particles grew in size at pH 8.5 and also as they became aggregated at pH 5.9. 

Determination of Fatty Acids in Cerebrospinal Fluid. II. Qualitative and Quantitative Studies by a Combination of Alkali Titration and Gas Chromatography Scand. J. Clin. Lab. Invest. 16(2) 139-144 (1964) CA 62 9605d... 

When the alkali titration per fraction falls to zero (after 10-12 fractions), change the eluent to methanol and continue collecting 10-ml fractions. Analyse by alkali titration, or by dilution and titration with benzethonium chloride. 

Mixtures of mono- and diester and phosphoric acid can be determined by alkali titration. 

The phosphate esters are converted to the free acid form, if they are present as salts, and determined by alkali titration. Monoesters have one weakly acidic and one strongly acidic proton. Diesters are strongly acidic. 

Extraction of ethoxylated alcohol (by deionisation) gives ether sulphate Fatty acid by petroleum ether extraction and alkali titration (lower ethoxylates also extracted) gives glyceride sulphate Extraction of fatty amine and acid titration (lower ethoxylates also extracted) gives sulphosuccinamate... 

Carboxylates with weakly basic cationics. As for quats. Results of acid-base titration must be interpreted bearing in mind the degree of protonation or deprotonation in the product acid titration measures free bases plus carboxylate anions, titration with alkali measures free acids plus protonated amine cations. If only weak acids and bases are present, acid titration measures the bases and alkali titration the acids. 

A commonly used method for determining acid content is alkali titration using an appropriate indicator [1-4], However, in this method, there is the possibility of error due to an inability to detect a subtle color change of the indicator in the transition range, especially in cases of colored samples. In addition, the titration method is not sufficiently sensitive to detect low acid content, and it requires large sample amounts and a great deal of time. Potentiometric titration is commonly recommended as an alternative method. 

If the ammonium salt being determined is fairly pure, an excess of N sodium hydroxide may be added to a known weight, the solution boiled until all ammonia is evolved and the excess of alkali titrated back with N acid to methyl orange. 1 ml N — 0 01703 g NH3. 

In Chapter 1 (page 15) we learnt that indicators are used to detect the end-point in acid-alkali titrations. You may also have used indicators such as litmus to test whether a substance is acidic or alkaline. In this section we shall look more closely at how specific indicators are used in titrations involving strong and weak acids and bases. 

Sodium Hydroxide, Standard Solutions (0.03 M)— Prepare by mixing 7 parts of water with 3 parts of standtud 0.1 A/sodium hydroxide (NaOH) solution. Concentrate 400 mL of 0.03 Af NaOH solution by evaporating to 30 mL, and determine any sulfate present in accordance with Appendix Al, Turbidimetric Procedure for Sulfate of Test Method D 1266. If sulfate is found, corrections must be made for any sulfur introduced by the reagent in the alkali titration following combustion. 

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