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.
116/734
![But, Oli tho otlicr haiid, sincc thè various charactcristic Chemical reactions of individuai salts in solution are due to thè free ions and not to undissoeiated molecules of thè salta, \ve will have thè sanie eharaeteristic reaetions in an equi-moleeular solution of NaCl and KI, as in an equiniolecular solution of KCl + NaI or any mixture of these two Solutions. And therefore if tho equilibrium between these ions is altered by thè separation of part of thè ions in thè forni of insoluble or less soluble salts, thep a reaetion will really ooeur, and tliiis in thè ordinary way thè reaction proceeds cntircly in a given senso. Thus on concentrating thè solution by evaporation, at a eertain point those ions will unite and separato which forni a less soluble salt {see preparation of potassium nitrato or conversi on nitrato). Again on adding barium chloride to a solution of sodium sulphate, bariuni sulphato is fornied and separates, because it is insoluble, and then all thè sodium sulphate can be transformed and separated in thè form of insoluble barium sulphate. These true ehemieal reactions are, however, accompaniod by measurable thermal phenomena. The sanie niay be said when by mixing two electrolytes two of thè four types of ions whieh are fornied have great affinity to one another and unite to forni a substanee w'hich has little tendency towards dissociation. In this ease true combination of thè ions, that is, true ehemieal combination, occurs. Thus on mixing two strongly dissociated substances, sudi as hydrochloric acid solution and sodium acetato, thè forniation of NaCl and aeetic acid is possible, bccause NaCl has a great tendency to dissociation and is therefore not fornied, wliilst, on thè other hand, aeetie acid being a weak acid is only slightly dissociated and thè affinity between thè H ions and those of thè acetic acid being very great, undissoeiated aeetie acid is easily fornied. This faet explains how in praetice thè strong acids readily liberate thè weak acids from thè corresponding salts, and how strong bases liberate weak bases from their salts, beeause thè H cations of thè aeid have a great affinity for, and tend to unite with, thè anions of thè weak acid, whilst thè OH anions of thè base have great affinity for and tend to unite with thè cations of thè weak base ; thus caustic soda liberates ammonia from ammonium salts. In 1908 Rosenstiehl stated that doublé deeomposition between salts, as in thè case of organie esters, is always preeeded by hydrolysis, by means of an intermediate reaction with one or more moleeules of water, for example : MeCl + HOH = MeOH + HCl ; [+ AgNOg] = AgCl + Me.Noa + HgO. He called thè salts and ethers which are slowly hydrolised bradolytes, wliilst those whieh are rapidly hydrolised he called stenolytes. ANALYTICAL TESTS FOR THE IONS. The extraordinary simplicity of thè tests used in analytical ehemistry is explained by thè ionie tlieory, because in a solution of niany salts we do not require to recognise thè properties of all thè salts, but siniply those of thè respective ions, which possess properties common to many salts. If, for example, we have a solution which contains 50 anions and 50 cations, these would be theoretically able to form 2500 salts, and if all these salts possessed individuai charaeteristie reactions, it would be necessary to verify thè presence of 2500 substances. Silice, on thè other hand, salts in aqueous solution aro dissociated into their ions, all that is necessary to completely analyse this solution is to confimi thè presence of 100 ions (50 anions and 50 cations). But eertain apparent abnormalities in analytical ehemistry ean also be explained by thè new theory of eleotrolytic dissociation. We know, for example, that silver nitrato is thè safest reaction and an almost generai one for tho detection of chlorinc, bccause thè cation of silver (in tho soluble nitrato) unitos with thè anion, chlorine (of any soluble chloride) with thè separation of thè white insoluble substanee silver chloride. Now whilst this reaction occurs with hundreds of chlorinated compounds and with all soluble chlorides, eertain other compounds which also contain chlorine, sudi as potassium chlorate, chloro- form, ehloroaeetic acids, &c., givo no precipitate with silver nitrate. By thè electrolytic dissoeiation theory we know, in fact, that thè formation of silver chloride by means of soluble silver salts is a reaetion charaeteristie of ehlorine ions, but chloroform is not a salt and is not dissociated, and therefore cannot give this reaction. Potassium chlorate (CIO3K) is a salt, but in aqueous solution it is dissoeiated into its ions, one of which is potassium (K) and thè other thè chlorie acid residue (CIO3), which is different from thè chlorinc ion and thus docs not give thè reaction with silver nitrate. VALENCY OF THE IONS. Molecules dissociated into favo ions also exercise doublé thè normal osmotic pressure, and in thè case of very dilute sulphuric acid, three tiine^} thè osiiiotic pressure whicll y ould be deduced](https://iiif.wellcomecollection.org/image/b28134187_0118.jp2/full/800%2C/0/default.jpg)
