Theoretical organic chemistry / by Julius B. Cohen.

  • Cohen, Julius B. (Julius Berend), 1859-1935.
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: Theoretical organic chemistry / by Julius B. Cohen. Source: Wellcome Collection.

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    Example.—07010 gram of a mono-acid salt gave 0-2303 gram platinum. 7010 x iqi; --— = 594*2. •2303 This represents the molecular weight of the salt, from which the weight of H2PtCl6 must be deducted and the result halved. 594-2-409-9 M 2 = 92-15- One or other of the above physical and chemical methods for determining molecular weights will be found applicable to the majority of organic compounds. Only such substances are excluded as, being neither acids nor bases, are non-volatile or insoluble in any solvent. It is obvious that examples of this kind are rare. The molecular weight can only be approximately estimated by breaking up the compound into simpler constituents of known molecular weight. Such is the case with the starch molecule, which is non-volatile, and decomposes on dissolving- in water. The molecular weight of soluble starch (p. 293) has been ascertained by the cryoscopic method. It follows that the insoluble starch molecule from which soluble starch is formed has not a smaller, but probably a larger, molecular weight. Cellulose, which cannot be dissolved unchanged in any solvent, is another example of a substance the molecular weight of which cannot be determined. Its formula is therefore written (C6H10O5)n. Questions on Chapter III 1. A substance gave the following analytical result C = 54-5 ; H = 9-09 ; O = difference. A vapour-density determination by V. Meyer’s method gave the following result :—o‘i gram of the substance displaced 27 c.c. of air measured at 150 and 745 mm. pressure (vapour tension at 15°= 12 -7 mm.). Determine the molecular formula. 2. The following two results were obtained with Landsberger’s boiling- point apparatus, using alcohol as solvent. Calculate the mean molecular weight of the substance. Weight of substance. Volume of solvent. Riseofb.p. i-oigrm. 24-2 c.c. -535° i-oigrm. 257 c.c. -519° The sp. gr. of alcohol at the b.p. = 0-7422.