Boiling point of solution

Figure 14.1. Boiling point of solutions of sodium chloride as a function of the boiling point of water.

Boiling Point Boiling point of solution is higher than solvent... 

We turn now to the T-xB boiling-point diagram (7.43) at fixed pressure (e.g., P= 1 atm). Under these conditions, the T-xeq curve displays the quantitative variation of the normal boiling point of solution as a function of liquid concentration. The boiling-point diagram therefore provides a basis for exact theoretical analysis of the ancient art of distillation, a staple of chemical laboratory practice. 

BECKMANN, ERNST (1853-1923). Beckmann was a German chemist who discovered in 1886 the arrangement of oximes of ketones into acid amides or anilides, named the Beckmann molecular transformation. He was the inventor of two pieces of apparatus used in determining freezing and boiling points of solutions. The Beckmann thermometer is used for determining molecular weights in solutions. 

Pig, 95.—Boiling Points of Solutions of Nitric Acid with and without Sulphuric Acid. 

In this method, the boiling points of solutions of known concentration are compared to that of the solvent, at the same temperature. Tlie apparatus tends to be complicated, and errors are possible from ambient pressure changes and the tendency of polymer solutions to foam. Present-day commercial ebulliometers are not designed for molecular weight measurements in the range of major interest with synthetic polymers. The method is therefore only used in laboratories which have designed and built their own equipment. 

DP, boiling point of solutions saturated with magnesium sulphate on increasing content of potassium sulphate. 

Table IX.—Boiling Points of Solutions of Potassium and Sodium Hydroxides BETWEEN 100° AND OVER 300° FOR DIFFERENCES OF 10°.

If the pressure is other than 1 atm, the temperature can be read from the steam tables. Given this boiling point for pure water, we can look up the boiling point of solutions of NaOH from a Duhring chart (see p500 of Geonkoplis) ... 

Elevation of boiling point — AT/, — (boiling point of solution) - (boiling point of solvent) = AT w... 

The boiling points of solutions increase with increased pressure. 

Consideration of these characteristics makes it clear that only very special liquid pairs could conceivably form ideal solutions. It would be necessary that the molecules of the constituents be very similar in every respect, for example in structure, size, and chemical nature. Thus, solutions of optical isomers, adjacent members of an homologous series, and similar mixtures would be expected to be nearly ideal, but actually all solutions can at best only approach ideality as a limit. Solutions which form immiscible liquid phases are of necessity extremely nonideal, and extraction operations depend upon this. The extent to which solutions depart from ideality is manifested by deviations of the properties of the solutions from the characteristics listed above, and a study of these deviations will permit us to some extent to predict their behavior in extraction operations. The most useful characteristics of the ideal solution for these purposes is that of vapor pressure, since considerable information has now been accumulated for many mixtures on this and related properties such as boiling points of solutions, azeotropism, and vapor-liquid equilibria. Classifications of compounds according to the effect of intermolecular forces on properties of mixtures also provide much useful material, but the second and third characteristics in the list above are of limited value owing to lack of experimental data to which we can refer. 

The boiling point of solutions is calculated by substituting into the preceding equation as the following example demonstrates. 

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