Carbonate mixtures with hydroxide, titration

Figure 7-5. Titration of 100.0 ml of hydroxide-carbonate mixture with 0.2062 HCl. (a) pH vs. ml titration curve, (b) Gran function plots revealing three equivalence points 18.7 ml, and two further segments of 10.3 ml each.

The two methods available for this determination are modifications of those described in Section 10.32 for hydroxide/carbonate mixtures. In the first procedure, which is particularly valuable when the sample contains relatively large amounts of carbonate and small amounts of hydrogencarbonate, the total alkali is first determined in one portion of the solution by titration with standard 0.1M hydrochloric acid using methyl orange, methyl orange-indigo carmine, or bromophenol blue as indicator ... 

Acidimetric titrations of carbonates and their mixture with either hydroxide or bicarbonate are simple to carry out with acid-base indicators or potentiometrically using a glass electrode and a pH meter. 

When the mixture is titrated with standardised HCl using bromophenol blue indicator, the titre gives the total (carbonate + hydroxide) content. In another aliquot the carbonate is precipitated as barium carbonate and the hydroxide is determined by titration with the acid using thymol blue indicator (without need to filter barium carbonate). The second titre gives the hydroxide content of the solution. 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

The phosphorodichloridate was hydrolyzed by adding to a stirred solution of sodium carbonate (253 grams) in water (2.9 liters). After 1 hour the solution was cooled and acidified with a solution of concentrated sulfuric acid (30 ml) in water (150 ml) and then extracted with a mixture of tetrahydrofuran and chloroform (2.3/1 3 x 1 liter). The tetrahydro-furan/chloroform liquors were bulked and evaporated to dryness to give a light brown oil. This was dissolved in water (1 liter) and titrated with 2N sodium hydroxide solution to a pH of 4.05 (volume required 930 ml). The aqueous solution was clarified by filtration through kieselguhr and then evaporated under reduced pressure to a syrup (737 grams). 

Carbon dioxide is not a common oxidation product in periodate work, but it does appear in the oxidation of ketoses,49 a-keto acids,14,39 and a-hydroxy acids,14 39 and it is often a product23 141 of overoxidation. Carbon dioxide analyses have been carried out using the Plantefol apparatus,49 the Warburg apparatus,14 23 and the Van Slyke-Neill mano-metric apparatus,39 and by absorption in standard sodium hydroxide141 followed by back-titration with acid. A most convenient method is the very old, barium hydroxide absorption scheme.16 The carbon dioxide is swept from the reaction mixture into a saturated, filtered barium hydroxide solution by means of a stream of pure nitrogen. The precipitated barium carbonate is filtered, dried, and weighed. This method is essentially a terminal assay. The manometric methods permit kinetic measurements, but involve use of much more complicated apparatus. 

A 500-mL, four-necked, reaction flask, equipped with a mechanical stirrer, thermometer, and glass pH electrode combined with an automatic titrator (Note 1), is charged with sodium (meta)periodate (85.5 g, 0.4 mol) (Note 2) and water (200 mL). The suspension is cooled to 0°C in an ice bath and 3 N sodium hydroxide (about 133 mL, 0.4 mol) is added dropwise at a rate such that the temperature does not exceed 7°C. The final pH of the suspension is 5.5. The cooling bath is removed and finely powdered 5,6-0-isopropylidene-L-gulono-1,4-lactone (Note 3) (43.6 g, 0.2 mol) Is added in one portion. The temperature of the mixture is kept below 30°C (Note 4). The pH of the suspension is maintained at 5.5 during the course of the reaction by addition of aqueous 15% sodium carbonate (about 15 mL). The suspension is further stirred at room temperature for 30 min, saturated with sodium chloride (105 g), and filtered by suction using a Buchner funnel. The white solid (Note 5) is washed thoroughly with two, 50-mL portions of brine and the pH of the combined aqueous layers is adjusted to... 

Permanent hardness can also be estimated by the alkalimetric method of Wartha and Pfeifer. A measured volume (200 e.e.) of the water is boiled with 50 c.e. of a mixture of decmormal solutions of sodium carbonate and hydroxide in equal amounts after restoring to the original volume and allowing the solution to settle, the residual alkali is determined by titration with standard acid. As the bicarbonates do not cause any consumption of alkali, there is a direct proportionality between the quantity of alkali which disappears and the total amount of sulphates and chlorides of calcium and magnesium. Sodium carbonate alone does not efficiently precipitate magnesium salts from solution, but precipitation as the hydroxide is complete if excess of sodium hydroxide is present it is for this reasoii that a mixture of sodium carbonate and hydroxide is applied 3 (see also p. 211). 

Record the volume, Va, of the 0.02 N sodium hydroxide used. Add 500 mg of sodium bicarbonate and 10 mL of 2 N sulfuric acid, and then after evolution of carbon dioxide has ceased, add 1 g of potassium iodide. Stopper the flask, shake the mixture, and allow it to stand in the dark for 5 min. Titrate the liberated iodine with 0.02 N sodium thiosulfate to the sharp disappearance of the yellow color, confirming the endpoint by the addition of a few drops of starch TS. Record the volume of 0.02 N sodium thiosulfate required as Fa. 

Sodium Hydroxide, 1N (40.00 g NaOH per 1000 mL) Dissolve about 40 g of sodium hydroxide (NaOH) in about 1000 mL of carbon dioxide-free water. Shake the mixture thoroughly, and allow it to stand overnight in a stoppered bottle. Standardize the clear liquid as follows Transfer about 5 g of primary standard potassium biphthalate [ KHCgH4(COO )2], previously dried at 105° for 2 h and accurately weighed, to a flask, and dissolve it in 75 mL of carbon dioxide-free water. If the potassium biphthalate is in the form of large crystals, cmsh it before drying. To the flask add 2 drops of Phenolphthalein TS, and titrate with the sodium hydroxide solution to a permanent pink color. Calculate the normality. Each 204.2 mg of potassium biphthalate is equivalent to 1 mL of 1 N Sodium Hydroxide. 

Quantitatively transfer the contents of the conical flask into a 500-mL distillation flask fitted with a Kjeldahl trap and a water-cooled condenser, the delivery tube of which extends well beneath the surface of a mixture of 150 mL of carbon dioxide-free water and 20.0 mL of 0.1A hydrochloric acid in a receiving flask. To the distillation flask add 20 mL of a 1 10 sodium hydroxide solution, seal the connections, and then begin heating carefully to avoid excessive foaming. Continue heating until 80 to 120 mL of distillate has been collected. Add a few drops of methyl red TS to the receiving flask, titrate the excess acid with 0.1 A sodium hydroxide, and record the volume required, in mL, as Sa- Perform a blank determination on 20.0 mL of 0.1A hydrochloric acid, and record the volume required, in mL, as Ba. Record the amide titer (Ba-Sa) as V3. 

Because all cell culture media are carbonate-buffered systems, the pH is dependent on the CO2 in solution, which in turn is in equihbrium with the CO2 in the gas phase. This offers the opportunity of using the CO2 concentration within the gas phase for gentle, very efficient pH control (Figure 5.10.1). Alternatively, or in addition, pH control is possible by using base titration (acid titration is given by CO2 anyway). When using hydroxide, one should use a 1 M mixture of NaOH and KOH (95 5) to avoid too great a shift in Na/K ratio and osmolarity. 

The accuracy of analytical methods for solutions containing mixtures of carbonate and hydrogen carbonate ions or carbonate and hydroxide ions can be greatly improved by taking advantage of the limited solubility of barium carbonate in neutral and basic solutions. For example, in the Winkler method for the analysis of carbonate/hydroxide mixtures, both components are titrated with a standard acid to... 

Hexanedione (acetonylacetone) Exactly 3% (titrated) sodium hydroxide solution (100 ml) is poured over diethyl 2,3-diacetylsuccinate (10 g), a soda-lime tube is attached to the flask, and the whole is heated on a water-bath until after 2-3 h no diacetylsuccinate is precipitated on acidification of a sample. The mixture is allowed to cool, then saturated with potassium carbonate. Oily diketone separates and is removed. The alkaline layer is extracted twice with ether, and these extracts are united with the separated diketone and the mixture is dried and distilled. Much diketone distils with the ether, but if the foreruns are worked up a total yield of 90% (4 g) of 2,5-hexanedione, b.p. 194°, is obtained. 

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