Constant-boiling mixture

At z in the curve, however (the minimum of vapour pressure), the solution and vapour are in equilibrium and the liquid at this point will distil without any change in composition. The mixture at z is said to be azeotropic or a constant boiling mixture. The composition of the azeotropic mixture does vary with pressure. 

The acid which comes over is a constant boiling mixture containing about 47 hydrogen bromide (density = 1.46 g cm... 

Properties—Hydrogen iodide is a colourless gas. It is very soluble in water and fumes in moist air (cf. hydrogen chloride), to give hydriodic acid. Its solution forms a constant boiling mixture (cf. hydrochloric and hydrobromic acids). Because it attacks mercury so readily, hydrogen iodide is difficult to study as a gas, but the dissociation equilibrium has been investigated. 

As a guide to the probable occurrence of a constant-boiling mixture, it should be noted that such mixtures most frequently occur when one of the components contains an hydroxyl (— OH) group. Only aqueous and alcoholic mixtures therefore are likely to have a constant boiling-point. 

Liquids are occasionally purified by removing impurities as constant-boiling mixtures, or by shaking with concentrated sulphuric acid and subsequently separating the dried liquid from the acid the second method is therefore limited to liquids which are insoluble in, and chemically unaffected by, the strong acid e.g., benzene, anhydrous chloral). 

Table 5.11 Binary Azeotropic (Constant-Boiling) Mixtures 5.58...

Hydrogen chloride and water form constant boiling mixtures. The properties of these mixtures, determined with great accuracy, and often used as analytical standards (16), are summarized in Table 6 and graphically depicted in Figure 3. 

Fig. 1. Indirect hydration process for the manufacture of isopropyl alcohol CBM = constant boiling mixture (61,62).

Azeotropic distillation. In some cases two or more liquids form constant-boiling mixtures, or azeotropes. Azeotropic mixtures are most likely to be found with components which readily form hydrogen bonds or are otherwise highly associated, especially when the components are dissimilar, for example an alcohol and an aromatic hydrocarbon, but have similar boiling points. 

In azeotropic distillation, the added component is a chemical that forms an azeotrope (constant-boiling mixture) which boils at a lower temperature than any of the constituents of the feed. For example, addition of certain ketones to narrow cut mixtures of paraffins, naphthenes, and an aromatic is known to form azeotropes with the paraffins and naphthenes which boil at temperatures low enough to permit relatively easy separation of them from the aromatic. 

This test, which is frequently referred to as the Huey test, was first described and used by W. R. Huey in 1930, and since that time it has had wide application, particularly in the USA. The test consists of exposing the specimens (20-30 cmin fresh boiling 65% HNO3 (constant boiling mixture) for five successive periods of 48 h each under a reflux condenser. The specimens are cleaned and weighed after each period, and the corrosion rate (as a rate of penetration) is calculated for each period of test and for the average over the five periods corrosion rates are expressed as mm/y. The reason for the... 

As it is difficult to prepare ter /-butyl alcohol free from water, 84 g. of the constant boiling mixture of the alcohol and water can be used. This mixture boils at 8o°, contains 88.24 per cent alcohol when the distillation is carried out at 760 mm., and can be readily obtained by distilling a sample of the dilute alcohol. 

Azeotrope formation, constant boiling mixtures in deaerators... 

Constant boiling mixtures in deaerators, of amines 511 Contaminant binding, caused by oily surfaces 298... 

All of the hydrogen halides are very soluble in water, and acidic solutions result. Although HF is a weak acid, the others are strong and are almost completely dissociated in dilute solutions. HC1, HBr, and HI form constant-boiling mixtures with water that contain 20.2%, 47.6%, and 53% of the acid, respectively. 

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