Satisfactory ending

Hydrazine hydrate may be titrated with standard acid using methyl orange as indicator or, alternatively, against standard iodine solution with starch as indicator. In the latter case about 0-1 g., accurately weighed, of the hydrazine hydrate solution is diluted with about 100 ml. of water, 2-3 drops of starch indicator added, and immediately before titration 6 g. of sodium bicarbonate are introduced. Rapid titration with iodine gives a satisfactory end point. 

The Bronsted-Lowry theory of acids and bases referred to in Section 10.7 can be applied equally well to reactions occurring during acid-base titrations in non-aqueous solvents. This is because their approach considers an acid as any substance which will tend to donate a proton, and a base as a substance which will accept a proton. Substances which give poor end points due to being weak acids or bases in aqueous solution will frequently give far more satisfactory end points when titrations are carried out in non-aqueous media. An additional advantage is that many substances which are insoluble in water are sufficiently soluble in organic solvents to permit their titration in these non-aqueous media. 

Procedure. Weigh out accurately from a weighing bottle about 0.2 g of the pure sodium carbonate into a 250 mL conical flask (Note 1), dissolve it in 50-75 mL of water, and add 2 drops of methyl orange indicator (Note 2) or preferably of methyl orange-indigo carmine indicator (Section 10.9), which gives a very much more satisfactory end point (Note 3). Rinse a clean burette three times with 5 mL portions of the acid fill the burette to a point 2-3 cm above the zero mark and open the stopcock momentarily, in order to fill the jet with liquid. Examine the jet to see that no air bubbles are enclosed. If there are, more liquid must be run out until the jet is completely filled. Re-fill, if necessary, to bring the level above the zero mark then slowly run out the liquid until the level is between the 0.0 and 0.5 mL marks. Read the position of the meniscus to 0.01 mL (Section 3.12). 

Notes. (1) The usefulness of the HHSNNA indicator for the titration of calcium depends upon the fact that the pH of the solution is sufficiently high to ensure the quantitative precipitation of the magnesium as hydroxide and that calcium forms a more stable complex with EDTA than does magnesium. The EDTA does not react with magnesium [present as Mg(OH)2] until all the free calcium and the calcium-indicator complex have been complexed by the EDTA. If the indicator is added before the potassium hydroxide, a satisfactory end-point is not obtained because magnesium salts form a lake with the indicator as the pH increases and the magnesium indicator-lake is co-precipitated with the magnesium hydroxide. 

It may be noted that very weak acids, such as boric acid and phenol, which cannot be titrated potentiometrically in aqueous solution, can be titrated conductimetrically with relative ease. Mixtures of certain acids can be titrated more accurately by conductimetric than by potentiometric (pH) methods. Thus mixtures of hydrochloric acid (or any other strong acid) and acetic (ethanoic) acid (or any other weak acid of comparable strength) can be titrated with a weak base (e.g. aqueous ammonia) or with a strong base (e.g. sodium hydroxide) reasonably satisfactory end points are obtained. 

If the analyte metal ion forms a stable EDTA complex rapidly, and an end point can be readily detected, a direct titration procedure may be employed. More than thirty metal ions may be so determined. Where the analyte is partially precipitated under the reaction conditions thereby leading to a slow reaction, or where a suitable indicator cannot be found, back titration procedures are used. A measured excess of EDTA is added and the unreacted EDTA titrated with a standard magnesium or calcium solution. Provided the analyte complex is stronger than the Ca-EDTA or Mg-EDTA complex a satisfactory end point may be obtained with eriochrome black T as indicator. An alternative procedure, where end points are difficult to observe, is to use a displacement reaction. In this case, a measured excess of EDTA is added as its zinc or magnesium complex. Provided the analyte complex is the stronger, the analyte will displace the zinc or magnesium. 

Although a variety of interpretations have been issued, reversibility to bronchodilators is considered to be present when the FEV i increases by 200 ml and 12% of the pre-bronchodilator value. Although in the latest GINA guidelines this issue is no longer addressed, the same criteria have been used for evaluation of the response to corticosteroids. A corticosteroid trial compared spirometric tests before and at the end of oral prednisolone (e.g. 30 mg/d) taken for two weeks or a course of inhaled steroid (e.g. beclomethasone 500 pg twice daily or equivalent) taken for six weeks. A positive response to corticosteroids justified prescription of regular inhaled steroid. Subjective improvement as a single efficacy parameter is not considered to be a satisfactory end point. Objective improvement is seen in 10-20% of patients with COPD. 

The larger the difference in standard potential between titrant and analyte, the greater the break in the titration curve at the equivalence point. A redox titration is usually feasible if the difference between analyte and titrant is a 0.2 V. However, the end point of such a titration is not very sharp and is best detected potentiometrically. If the difference in formal potentials is a 0.4 V. then a redox indicator usually gives a satisfactory end point. 

Displacement reactions may be treated as neutralizations from the standpoint of the foregoing discussion. If the acid or base displaced is moderately weak, i.e., ka or kh is about 10 the displacement reaction is equivalent to the neutralization of a very weak base or acid, with kh or ka equal to 10 , respectively no indicator is likely to give a satisfactory end-point in aqueous solution, although one may possibly be obtained in an alcoholic medium (cf. p. 396). If the acid or base being displaced is very weak, e.g., carbonic acid from a carbonate or boric acid from a borate, there is a marked pH inflexion at the equivalence-point which can be detected with fair accuracy by means of an indicator. 

An alternative, simpler, procedure for improving the inflexion in the neutralization of an amino-acid is to add formaldehyde to the solution although this does not affect the acid-titration curve, the one for alkaline titration is changed, as seen in Fig. 107. The effect of the formaldehyde is to increase the strength of the ammonium ion acid which is being titrated, and so the pH inflexion at the equivalence-point becomes much more obvious. This is the basis of the formol titration of amino-acids discovered by Sorensen (1907) approximately 10 per cent of formaldehyde is added to the solution which is then titrated with standard alkali using phenolphthalein as indicator. In the presence of thii concentration of formaldehyde the pH-neutralization curve has a sharp inflexion in the region of pH 9, and so a satisfactory end-point is possible with the aforementioned indicator. 

In case 1 a binary mixture of fine and coarse granules was blended to a satisfactory end-point. The blend was next emptied into a bucket elevator and thence to a hopper through a central feed point. The material was then fed, in 60 kg lots, to an extruder to produce an unacceptable finished product. The process started with a mixing operation followed by a segregating operation in the hopper. The central region (core) of the hopper contents was rich in fines and the outer regions rich in coarse, hence the initial feeds to the extruder contained an excess of fines whereas later feeds contained an excess of coarse. Since a bimodal mixture such... 

Sodium oxalate has been used as a primary standard substance for Ce(IV) in sulfuric acid. In the absence of a catalyst a temperature of 70 to 75°C is necessary. Smith and Getz found that in 1 to 2 M perchloric acid solution, sodium oxalate can be titrated at room temperature with Ce(IV) perchlorate or nitrate but not with sulfate. Rao, Rao, and Rao carried out the titration at room temperature in the presence of barium chloride to remove sulfate, which retards the reaction between oxalate and Ce(IV) and between oxalate and oxidized ferroin. Alternatively, some Fe(III) was added, and the trace of Fe(II) produced photochemically then reacted with the indicator. Rao, Rao, and Murty carried out the titration in 0.5 M HNOj with ammonium hexanitratocerate(IV) instead of the sulfate. With a small amount of KI and KIO3, a satisfactory end point was obtained at room temperature with ferroin as indicator. 

The Effect of Reaction Completeness on Titration Curves Figure 13-5 illustrates the effect of solubility product on the sharpness of the end point in titrations with 0.1 M silver nitrate. Clearly, the change in pAg at the equivalence point becomes greater as the solubility products become smaller, that is, as the reaction between the analyte and silver nitrate becomes more complete. By careful choice of indicator—one that changes color in the region of pAg from 4 to 6—titration of chloride ion should be possible with a minimal titration error. Note that ions forming precipitates with solubility products much larger than about 10 do not yield satisfactory end points. 

A Teutralization titrations are widely used to determine the concentration ofana-J V lytes that are themselves acids or bases or are convertible to such species by suitable treatment J Water is the usual solvent for neutralization titrations because it is readily available, inexpensive, and nontoxic. Its low temperature coefficient of expansion is an added virtue. Some analytes, however, are not titratable in aqueous media because their solubilities are too low or because their strengths as acids or bases are not sufficiently great to provide satisfactory end points. Such substances can often be titrated in a solvent other than water. We shall restrict our discussions to aqueous systems. 

Several operational procedures must be observed in order to obtain products with satisfactory end quality using most types of conventional equipment, without the inclusion of special modifications such as screws or matrixes with specific designs. Extrusion or injection processes can use typical polymer processing screws (L/D of 20 1) designed to minimise the exposure time of the melted biopolymer. After use, the equipment can be purged using low-density polyethylene (PE) resin as a vehicle [29]. 

From disussions with jelly, jam, and marmalade producers in different parts of the world, it was learned that shortcomings of the SAG test with regard to final product characteristics, induced jam and jelly producers to develop other methods to determine the dosage of a particular pectin required to obtain a satisfactory end-product ( ). 

The story must come to a satisfactory ending (which does not necessarily mean a happy ending). 

Hypervariable DNA sequences have revolutionised forensic science. They can reveal so much information that the probability of a chance match between two individuals is vanishingly small. They can also be used, with slightly less power, to demonstrate close relationships between individuals from a wild population. Their use in studying relationships in wild populations is limited in two ways. Firstly, their high mutation rates make them unsuitable for the study of distant relationships such as that between individuals from different populations. Secondly, it should always be remembered that the establishment of the relatedness between individuals in a wild population, even if it was possible, is not a satisfactory end in itself. We... 

A Quality Assurance Program should be conducted to assure satisfactory end-product strength and durability. This should (1) establish limits on bonding factors to ensure acceptable joint and end-product (2) monitor the production processes and quality of bond in joint and end-product and (3) enable detection of unacceptable joint and end-product, detenmning the cause, and correcting the problem [3]. 

Tubes 4 to 10 feet long, often 2 to 3 inches in diameter, are located vertically inside a steam chest enclosed by a cylindrical shell. The first vertical tube evaporators were built without a downcomer. These were never satisfactory, end the central downcomer appeared very early. There are many alternatives to the center downcomer different cross sections, eccentrically located downcomers, a number of downcomers scattered over the tube layout, downcomers external to the evaporator body. 

For most work in pharmaceutical analysis classical methods have now been superseded by complexometric titration. Determination of calcium by itself presents little difficulty and two basic procedures are applicable, (i) titration at pH 10 in ammonia buffer using solochrome black as indicator and (ii) titration at pH 12 to 13, either in diethylamine using alizarin black (diadem chrome black) or in potassium hydroxide solution using Patton and Reeder s indicator. Provided a small quantity of complexed magnesium is included for titration (i) sharp and satisfactory end-points are obtained by these methods and there is no significant difference in the results obtained at the two pH values if a pure calcium compound is titrated. Difference in the two results would be expected if the calcium salts were contaminated with magnesium, when the titration at pH 10 would include both ions and that at the higher value the calcium only. 

Two methods which are quite widely applicable to many local anaesthetics are non-aqueous titration (perchloric acid to crystal violet, p. 792) and titration with sodium nitrite (0 5 g in 75 ml water and 10 ml hydrochloric acid, titrating with O IM nitrite and determining the end-point using the dead-stop technique, p. 867). A few materials such as benzocaine may be determined by both methods but in most cases either one or the other is applicable. Lignocaine hydrochloride, for example, gives a satisfactory end-point by the non-aqueous method but cannot be determined by titration with nitrite procaine hydrochloride on the other hand is satisfactorily titrated wdth nitrite but gives rise to a precipitate during titration in non-aqueous medium which obscures the end-point. Certain compounds such as amethocaine hydrochloride cannot be determined by either method. 

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