I
Paul A. Giguire
Universite Laval Quebec, P.Q., Canada
Textbook Errors, 115
II
Physical Properties of Pure Hydrogen Peroxide
In spite of contrary evidence of long standing pure hydrogen peroxide is still described in some chemistry texthooks as "a pale blue, syrupy liquid, freezing a t -0.89"C." This is all incorrect as the record shows. The Color of Hydrogen Peroxide
Liquid hydrogen peroxide, like water, is essentially transparent to visible light. Yet we know that the clearest water under great depth, as in deep-sea diving, lets through only the hlue-green portion of the sunlight. This is due to the very strong and broad vibrational hands of the water molecule in the infrared. Their overtones and combinations extend almost into the red, hence the ahsorption of that part of the visible radiation under great thickness. On that score alone hydrogen peroxide should behave much like water as may he gathered from the available data on its near infrared spectrum (I). At the other end of the spectrum, however, the situation is quite different. Whereas water is transparent in the ultraviolet as far as 190 nm (or 1900 A), hydrogen peroxide begins to absorb right at the limit of the visible, uiz., around 420 nm (2). From the slope of its absorption edge it may he expected to appear yellowish under great thickness. Actually, visual inspection of flasks or carboys of hydrogen peroxide solutions, no matter how concentrated, reveals no particular color. The "pale blue" color still referred to must have originated in an early observation of the Rayleigh scattering of sunlight reflected through a column of liquid hydrogen peroxide 13). Very likely this was due to microscopic bubbles of oxygen from the catalytic decomposition hy traces of impurities. The "Syrupy" Liquid
More than 50 years ago Maass and Hatcher (4) in their pioneer investigation, showed that pure hydrogen peroxide is not much more viscous than water, as may be judged from the isotherms of the figure (5). The erroneous notion of a highly viscous liquid must have originated, as pointed out by Schumb, Satterfield, and Wentworth (6) in a term used by Thenard, the discoverer of hydrogen peroxide, to describe the great density of the pure liquid. Having succeeded in preparing a very concentrated sample (over 95% in weight) he went on to,write (7) ". . . le peroxide d'hydroghe est bien plus dense que l'eau. Pour s'en conuaincre . . . il suffit de le uerser dans l'eau: en effet, quoiqu'il soit trcs soluble, il code b trauers, comme une s6rte de sirop." This was not an appropriate comparison. Indeed, the reason one can see hydrogen peroxide trickling through water is not its greater viscosity, but rather its higher (by some 40%) density, and refractive index; 1.4067 compared with 1.3325 for water at ordinary temperature. It is true that concentrated hydrogen peroxide has a strong tendency to supercool, in which case it becomes very viscous. For instance, Cooper and Watkinson (8) have reported a value of 7 centipoises, that is 7m N s/mZ for a 86% solution supercooled to -40°C. However, any
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Viscosity of liquid mixtures of hydrogen peroxide and water. The viscosity 01 the deuterated compounds is also shown for comparison.
other liquid would show a similar increase in viscosity if it could he supercooled to the same extent. Under ordinary conditions pure hydrogen peroxide is almost as mohile as water. Incidentally, it is noteworthy that the isotopic deuterium peroxide is less viscous than heavy water at O"C as shown in the figure. The Melting Point
The determination of the true melting point of pure hydrogen peroxide is an exacting task. First, removal of the last traces of water from the sample requires extreme care (9). The difficulty is compounded further by the curious property of the crystalline hydrate, H z O ~2Hz0, . to catalyze the decomposition of the peroxide on melting (10). The above quoted datum, -0.89"C, dates back to 1928 111). Since then, a number of reinvestigations have confirmed that it is too low by nearly half a degree. The presently accepted value is based on low temperature adiabatic calorimetry measurements for the determination of the third law entropy (12). The purity of the sample, 99.98 mole 90,the highest ever reported, was ascertained from three physical criteria; namely (a) the variation of the melting temperature with the fraction of the sample melted; (h) the excess heat capakity of the solid in the premelting region, and (c) the extent of the eutectic halt. Extrapolation to 100% purity led to a triple point of 272.74'K (-0.42"C). After correction for the pressure effect, dpfdt = 0.007" atm-1, the exact melting point of pure hydrogen peroxide turns dut to be -0.41°C.
Suggestions of material suitable for this column and columns suitable for publication directly should be sent with as many details as possible, and particularly with reference to modem textbooks, to W. H. Eberhardt, SehOol of Chemistry, Georgia InstituteofTechnalogy,Atlanta, Georgia 30332.
Literature Cited (I) Bain, O.andGiw6re.P.A.. Con. J. Cham., 33.521(1955). (2) Phibbs. M. K.and Giguhe, P. A,. Can. J. Chem., PJ. 490 (19511. (3) Spring, W., Z omrg Chpm.. 8.424 (1635). (4) Maass, 0 ,andllafehcr. W., J A m e r . Cham. Sor., 42.2548(1920). (5) Phibbs, M.K.,and Giguire, P.A.. Can. J Chem., 29,173 11951). (6) Schurnb, W. C., Ssttorfioid, C. N., and Wentmrth. R. L.. ''Hydrogen Pemiid%" Reinhold Publiahingcom.. NelaY0.k. 1955, pp. 2cd
(7) Thenard. L. J., MOm. Aced. Sci. P&. 3.345 (1818). (8) Coowr. K.A,. and Watkinsan. J. ti., I d . P m d o ~ S a e .55.635 . (1957) (9) Gi&re. P. A.,BulL Sac. Chim.. 720(1954). (10) G i g u h , P. A.,sndGwffrion,P.. Con J. Re% 288.59J(19SO). (11) bthbenson. A. C.. Mathesan, G. L., and Maaas. 0.. J. Amer C h m Soe.. 8.
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