Analytical chemistry by unknow

Author:unknow
Language: eng
Format: epub
Tags: Chemistry, Analytic
Publisher: London, And New York, Macmillan and co.
Published: 1895-03-25T05:00:00+00:00

Mill

lily jiiiii

Tliird Tnethod, Classification of the acids into groups, — (a) The first two methods suffice only for a few of the acids which the given solution may contain. The remainder are systematically detected as follows. The various acids must be in solution as salts of the alkali metals or metals of Group II. Such solutions are prepared thus. The test with hydrochloric acid (see above) having been made, a separate portion of the liquid is precipitated, first with hydrogen sulphide (the accompanying tests may again be made), and then with ammonium sulphide. The solution in which the metab have been detected and separated may also be employed. The sulphides are filtered off, the excess of hydrogen sulphide and ammonium sulphide removed by boiling, and hydrochloric acid added. Such a solution, of course, cannot be used for the detection of arsenic acid, etc., hydrochloric acid (which has been added), or chloric acid (which decomposes when boiled with the latter). The tests for sulphuric and nitric acids are also more or less inexact. To detect these acids the solution must be prepared as follows.

(b) The second method of preparing the solution is more convenient than the first (the test for carbonic acid with hydrochloric acid must be made in a separate portion). The boiling solution is precipitated by sodium carbonate in slight excess, and filtered. The filtrate, containing the various sodium salts, is subjected to the reactions given below. Both methods are open to the objection that salts wliich are deposited from acid solutions on neutralisation (e.g., phosphates, etc.), may also be precipitated. In such cases, and also when the substance to be analysed is insoluble in water or acids, fusion with sodium carbonate must be employed (§ 107, Eemark).

The detection of the acids may be commenced directly in the first solution; that prepared by the second method must first be neutralised, by hydrochloric or nitric acid, as the case may be.

Before taking up the course of analysis itself, it may be well to discuss the classification of the acids into groups. This is based upon the solubility of the various barium and silver salts in water (and, to a certain extent, in acids). Barium chloride, added to the neutral solution, is the general reagent for Group I., silver nitrate in nitric acid solution, that

•/

270 ANALYTICAL CHEMISTRY metalloids

of Group 11. Group III. is composed of acids, the barium and silver salts of which are soluble in water.

Oroup I, —Barium chloride precipitates from neutral solution the barium salts of the following acids: chromic, thio-sulphuric, iodic, carbonic, silicic (these are all detected in the course of analysis for the metals), sulphuric, hydrofluosilicic (barium salts are insoluble in acids), phosphoric, boric, hydrofluoric (barium salts are soluble in acids). To these may be added arsenious and arsenic acids, which, however, have been detected among the metals. The silver salts of the acids of Group I. are insoluble in water, but dissolve in nitric acid.

Group IL —Silver nitmte precipitates in solutions acidified by nitric acid the

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.