Volume 10

A comprehensive treatise on inorganic and theoretical chemistry / by J.W. Mellor.

  • Mellor, Joseph William, 1869-1938.
Date:
1947-1952
Catalogue details

Licence: In copyright

Credit: A comprehensive treatise on inorganic and theoretical chemistry / by J.W. Mellor. Source: Wellcome Collection.

    186/980 (page 170)
    two atmospheres pressure, and therefore that the reducing power of such a soln. is very nearly the same as that of gaseous hydrogen. The e.m.f. of the combination measured above increases by 2-27 millivolts per degree rise of temp. From these data the heat of the reaction is readily calculated ; it is S204+2S03+2H20+2H' =H2+4HS03'—13,920 cals. Subtracting the known value, HS0'3=H'+S03 -700 cals., gives S204+2H20=H2+2HS03'(-13920-1400=)-15,320 cals. Consideration of the free energy of the reaction between hyposulphites and water leads to the conclusion that they become much less stable as the temp, rises, a rise of 10° increasing the equilibrium press, of hydrogen two and a half times. In alkaline soln. of hyposulphite and sulphite a fairly definite potential is established at a platinum electrode, but the nature of the reaction on which it depends has not been discovered. In soln. of hyposulphite and thiosulphate, or of thiosulphate and sulphite, no definite potential could be observed. The potentials measured were unaffected by the cone, of the thiosulphate. The chemical properties of hyposulphurous acid and the hyposulphites.—The acid is known only in dil. aq. soln. ; but O. Rossler said that it is more soluble in alcohol than in water. P. Schiitzenberger, and A. Binz found that aq. soln. of the hyposulphites decompose when warmed, forming only hydrosulphites ; but J. Meyer represented the reaction : 2Na2S204+H20=Na2S203+2NaHS03 ; and his results for the decomposition at 45°, 60°, and 80° are summarized by the curves shown in Fig. 42. The speed of the decomposition is slow at the start, it then rises to a maximum, and later on slows down. Part of the products of the decomposition react with the undecomposed salt, and consequently the velocity of decomposition is proportional both to the extent of the decomposition, x, and to the quantity of salt left undecom- posed, a—x; so that dxjdt=kx(a—x). E. Jellinek found k at 0° to be 0-00014 ; at 10°, 0-00023 ; at 20°, 0-00037 ; and at 30°, 0-00063. If *'=105*, ]0g *'=1-32+0-0350. The decomposition on heating is probably best represented: 2Na2S204+H20=Na2S203+2NaHS03. A. Lumiere and L. Seyewetz, and M. Bazlen and A. Bernthsen made some observations on this subject. K. Jellinek studied the de- composition of sodium hyposulphite in soln. of sodium sulphite or hydrosulphite ; and found that it can be represented as a unimolecular reaction dxjdt=k{a—x), where x signifies the amount decomposed at the time t. E. Jellinek found the velocity constant, *, to be, in the presence of NaHSOa . 10 15 27 33 15 30 per cent. k at 18° . 0-00007 0-00031 0-00002 0-00109 — — k at 32° . — — — — 0-00055 0-00250 C. K. Jablczynsky and Z. Warszawska-Rytel found that the rate of decomposition is accelerated by the addition of sodium chloride, and diminished by the addition of a colloid like gum arabic. Dilution retards decomposition. The speed of the reaction corresponds with two reactions of the first order. C. F. Schonbein, P. Schiitzenberger, and A. R. Frank showed that the decomposition is retarded in the presence of alkalies. Hence, technical operations with hyposulphites are conducted in alkaline soln. whenever possible. Acidic soln. decompose very quickly, for when a soln. of the sodium salt is acidified, it becomes yellow or orange, and much sulphur is separated. When hyposulphurous acid is liberated from its salts, it is readily hydrolyzed to sulphoxylic and sulphurous acids. H. Bassett and R. G. Durrant summarize the action: H0.S.0.S0.0H^(H0)2S.S02; by H0.S.0.S0.0H+H20=S(0H)2 +H2S03(t+H20+S02); and by S(0H)2+S02^(H0)2S.S02. Thus, two isomeric forms of H2S204 are assumed. The direct union of two sulphur atoms in (H0)2S.S02 indicates that the compound can probably be readily reduced to thiosulphate ; and WO 80 J 60 1 40 20 1 <5 S^5 <4! 5>o 0 20 40 60 80 Minutes Fig. 42.—The Effect of Temperature on the Decomposition of Neutral Aqueous Solutions of Sodium Hyposulphite.