Raoult sentence example
- P. Sabanezhev obtained the value 15,000 by Raoult's method for purified egg albumin.
- This method was used by Raoult.
- The experiments of Raoult on solutions of organic bodies in water and on solutions of many substances in some dozen organic solvents have confirmed this result, and therefore the theoretical value of the osmotic pressure from which it was deduced.
- In the limit of dilution when n is very small compared with N this gives Raoult's experimental law that the relative lowering is n/N, which we deduced from the osmotic law, and conversely from which the osmotic law follows, while for more concentrated solutions agreement is obtained by assigning arbitrary values to a, which, as we have seen, is 5 in the case of cane-sugar.
- Raoult (Comptes Rendus, 1886-87) employed other solvents besides water, and showed that the relative lowering for different solvents and different dissolved substances was the same in many cases for solutions in which the ratio of the number of gramme-molecules n of the dissolved substance to the number of molecules N of the solvent was the same, or that it varied generally in proportion to the ratio n/N.Advertisement
- If dp is the difference of vapourpressure of solvent and solution, and do the rise in the boiling-point, we have the approximate relation, n/N = d p/p = mLdo/Ro 2, Raoult's law,..
- The most important apparent exceptions to Raoult's law in dilute solutions are the cases, (I) in which the molecules of the dissolved substance in solution are associated to form compound molecules, or dissociated to form other combinations with the solvent, in such a way that the actual number of molecules n in the solution differs from that calculated from the molecular weight corresponding to the accepted formula of the dissolved substance; (2) the case in which the molecules of the vapour of the solvent are associated in pairs or otherwise so that the molecular weight m of the vapour is not that corresponding to its accepted formula.
- The values thus found agreed in the main with Raoult's law for dilute solutions (see Solutions).
- For strong solutions the discrepancies from Raoult's law often become very large, even if dissociation is allowed for.
- This assumption coincides exactly with Raoult's law for the relative lowering of vapourpressure, if a = 1, and agrees with it in the limit in all cases for very dilute solutions, but it makes a very considerable difference in strong solutions if a is greater or less than 1.Advertisement
- It appears that the relatively enormous deviations of CaC1 2 from Raoult's law are accounted for on the hypothesis that a=9, but there is a slight uncertainty about the degree of ionization of the strongest solutions at-50° C. Cane-sugar appears to require 5 molecules of water of hydration both at o° C. and at loo° C., whereas KC1 and NaCI take more water at loo° C. than at o° C. The cases considered by Callendar (loc. cit.) are necessarily limited, because the requisite data for strong solutions are comparatively scarce.
- But the agreement is very good so far as the data extend, and the theory is really simpler than Raoult's law, because many different degrees of hydration are known, and the assumption a = i (all monohydrates), which is tacitly involved in Raoult's law, is in reality inconsistent with other chemical relations of the substances concerned.
- Raoult's earliest researches were physical in character, being largely concerned with the phenomena of the voltaic cell, and later there was a period when more purely chemical questions engaged his attention.
- An account of Raoult's life and work was given by Professor van't Hoff in a memorial lecture delivered before the London Chemical Society on the 26th of March 1902.
- Experimental measurements of freezing points of various non-electrolytic solutions have been made by Raoult, Loomis, Griffiths, Bedford and others and numbers ranging round 1.85 found for this concentration.Advertisement
- It appears that the relatively enormous deviations of CaC1 2 from Raoult's law are accounted for on the hypothesis that a=9, but there is a slight uncertainty about the degree of ionization of the strongest solutions at-50Ã‚° C. Cane-sugar appears to require 5 molecules of water of hydration both at oÃ‚° C. and at looÃ‚° C., whereas KC1 and NaCI take more water at looÃ‚° C. than at oÃ‚° C. The cases considered by Callendar (loc. cit.) are necessarily limited, because the requisite data for strong solutions are comparatively scarce.