Freezing point of solution

If we take Dieterici s numbers for the vapour pressures, and Roloff s for the freezing-points, of solutions of potassium chloride, we can calculate the osmotic pressure (P0) from the two equations ... 

The changes in osmotic coefficients with temperature and concentration make it difficult to solve the above equations accurately, but accurate determinations of the composition and relative amounts of the concentrated liquid and ice can be made from phase diagrams which are plots of the freezing points of solutions versus their concentration. From these, it is possible to determine the exact NaCl concentration at any temperature. Examples are shown in Figure 9 for solutions of 0 to 2.0 M glycerol in 0.15 M NaCl. This figure nicely illustrates how the presence of glycerol reduces the concentration of NaCl in the residual unfrozen solution. 

Freezing Point Freezing point of solution is lower than solvent... 

Explain how osmometry is used to measure molar mass. What are the advantages of osmometry over measurements of boiling points and freezing points of solutions ... 

Fig. 5), which is generally employed for determining the freezing points of solutions. It consists of a tube furnished with a stirrer and with a very exact thermometer, divided into hundredths of a degree. This tube, containing the milk, is placed in an air-jacket and this in a vessel furnished with a stirrer and a thermometer and charged with a freezing mixture (3-4 parts of ice and 1 part of salt). 

Matignon7 has determined the freezing-point of solutions of sodium chloride of various concentrations. Some of his results are given in the table ... 

G, cryohydric point of potassium sulphate solution ( — 1 2°). BX, freezing point of solutions saturated with magnesium sulphate, with gradual increase of potassium sulphate content. 

The solubility of the hydrates of hydrochloric acid existing at low temperatures may be drawn in the under part of Fig. 38. We may here also start from the point 0° for pure water, and going along the curve of freezing points of solutions of hydrochloric acid reach the cryohydric point for HCI.3H2O at b then follow the solution of that hydrate, b c d, which at c has the same composition as the solid hydrate and ends at d with separation of the hydrate HCl. 2H2O then the curve for saturation... 

Lowering of freezing-points of solutions.— Let us see, from an example, the importance of this law. 

Bases, Neutral Salts.— As a base it forms salts, in which form the diazo compound is obtained by diazotization, and which though also unstable has been isolated in small quantities and the composition and properties determined. Of the three salts, the sulphate, chloride and nitrate, the first is the most stable and the last is the least stable. They are colorless crystalline neutral compounds soluble in water, difficultly soluble in alcohol and insoluble in ether. After being prepared by the ordinary diazo reaction, with sodium nitrite in cold acid water solution, they may be precipitated in crystalline form by the addition of alcohol and ether. If the diazotization is effected in alcohol solution by means of amyl nitrite or ethyl nitrite the crystals of the diazonium salt separate at once. These salts of diazo benzene all show true salt characteristics, e.g., they lower the freezing point of solutions. The diazo radical, (CeHs—N2—) is thus basic toward strong acids, and the hydroxide, the non-isolated hypothetical diazo benzene, CeHs—N2—OH, is the free base. It may be considered as the simplest aromatic diazo compound and the mother substance of all other members of the class. 

Tq and T are the freezing points of solution and solvent, TF is the molecular heat of fusion, and the heat of dilution of the solution.)... 

In the following we shall deduce some of the formulae for the osmotic pressure, and for the changes in the vapour pressure, boiling point, and freezing point of solutions, which can be derived from these two essentially distinct theories of solution. 

This has been called the ionic self-dehydration reaction 29. Only four of the five equilibria, Eqs. (3) to (7) are independent and it has been found convenient to discuss the self-dissociation in terms of Eqs. (3), (5), (6), and (7). Values for the corresponding equilibrium constants are given in Table II. The values at 10° were obtained from a detailed study (4, 0 of the freezing points of solutions of metal hydrogen sulfates, water, and disulfuric acid, each of which represses the selfdissociation equilibria in a different way. Table III gives the concentration of each of the products of the self-dissociation. The total molal concentration of 0.0424 at 10° corresponds to a freezing point of 10.625°... 

Lowering of freezing point = AT = (freezing point of solvent) - (freezing point of solution) = Kfm... 

Experiment 51. The Determination of Molecular Weights from the Freezing Points of Solutions. 

Experiment 52. The Determination of the Degree of Dissociation of Electrolytes from the Freezing Point of Solutions. 

A study of the freezing points of solutions of the tannins has yielded results that lead to the conclusion that they all possess very high molecular weights,—a fact in accord with their colloidal properties. Since the number of compounds formed as the result of their hydrolysis is relatively small it is probable that they are the result of the condensation, with the loss of the elements of water, of hydroxy benzoic acids, such as gallic acid and protocatechnic acid. Emil Fischer who studied this class of... 

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