Treatise on general and industrial inorganic chemistry / by Etore Molinari ; third revised and amplified Italian edition translated by Ernest Feilman.
- Ettore Molinari
- Date:
- 1912
Licence: In copyright
Credit: Treatise on general and industrial inorganic chemistry / by Etore Molinari ; third revised and amplified Italian edition translated by Ernest Feilman. Source: Wellcome Collection.
118/734
![produces doublé thè qiiantity of co]3per, that is, 63*6 grms. of copper foreach 35*5 grms. of clilorine ; thus in cupric chloride we ha ve a simple divalent copper cation Cu”, and 31*8 grms. of copper for every gramme-ion of mono- valent chlorine CV, whilst in cuproiis chloride we have a compound divalent cation of copper CU2” and 63*6 grms. of copper for each gramme-ion of mono- valent CI'. For this reason in practice salts with a minimum valency are electrolysed whenever practicable, because for equal consumption of energy a greater quantity of metal is separated in this v ay. We have thus arrived at conceptions of ionie valency without any addition to thè atomic hypothesis, simply basing our considerations 011 thè electro- lytic bellaviour of many substances in dilute solution, and we see how in these phenomena also we obtain a proof of thè existence of variable valency, in distinction to thè Constant valency which was supposed to exist until a short time ago, based 011 exclusively atomistic concejitions. We have also shown that valency is generally lower at high temperatures where compounds in a state of minimum oxidisation are often found, whilst at lower tempera- tures thè compounds are more stable and are generally present in a more highly oxidised condition. MOLS, NORMAL SOLUTIONS, AND VOLUMETRIC ANALYSIS. The behaviour of acids and bases in solution serves as thè basis of a whole department of analytical chemistry, that of volumetrie analysis. Bases and acids saturate one another through thè recij)rocal saturation of their characteristic ions. A divalent ion is equivalent to two monovalent ions, and three of these latter are equivalent to one trivalent ion. The quantity of matter which corresponds to each valency of thè ions is thè same as that which we know under thè name of combining weight or equivalent or stoi- chiometric vaine {see p. 21), and thus if we have a quantity of an acid or base corresponding to its equivalent expressed in grammes or gramme- equivalent, dissolved in one litre of an aqueous solution, this is thè quantity corresponding to one valency, or finally, thè quantity corresponding to a monovalent ion, and sudi a solution is called a normal solution. Sudi Solutions are used for thè determination of thè strength or concentration of any acid or base, that is, for thè determination of thè quantities of pure acid or base contained in a given volume of their Solutions whatever may be thè dilution in which they are present. For thè sake of brevity in thè clisciission of electrolytic phenomena, thè use of thè word mal to express thè quantity in grammes corresponding to thè molecular weight of a substance has been proposed ; but it was then found more practicable to cali thè quantity in grammes corresponding to thè ion, a mol-ion (gramme-ion), thus one mol-ion of CI = 35-5 grms. ; one mol-ion of H = 1*01 grm. ; one mol-ion of SO4 = 96 grms., &c. Thus in order to obtain a normal solution of hydrochloric acid (HCl), we must dissolve thè quantity of HCl corresponding to one mol-ion of hyclrogen (that is, to TOl grm., or 36-46 grms. of pure HCl) in sufficient water to forni one litre of solution. In order to obtain a normal solution of sulphuric acid, which contains a divalent SO4 anion corresponding to two monovalent H* cations, we must dissolve thè quantity corresponding to one mol-ion of H only, that is. H2SO4 98 —X— = —, = 49 grms. of thè pure acid. in sufficient water to forni one litre. In this case equal volumes of thè normal Solutions of HCl and of H2SO4 are equivalent and will satm-ate thè sanie quantity of a basic sub- stanco. The normal Solutions of bases always refer to one gramme-ion of OH, and in thè case of polybasic bases, a quantity in grammes is used corresponding to one OH anion, that is, to one mol-ion of OH. Equal volumes of normal Solutions of an acid and of a base exactly ncutraliso one another, because thè OH' anions of thè base unite with thè H‘ cations of thè acid to forni uiidissociatcd water, which is iicutral. dlie point of neutrality is](https://iiif.wellcomecollection.org/image/b28134187_0120.jp2/full/800%2C/0/default.jpg)
