SU136590A1 - Method for coulometric analysis of metals by precipitation - Google Patents

Description

Various methods for coulometric analysis of various substances are known: however, these methods almost completely use no deposition method, since until now an electrochemical process has not been found, as a result of which, with current efficiency in lOOVo, substances that could form hardly soluble with metal ions were generated compounds.

In the proposed method of coulometric analysis by the method of deposition, generator electrodes from sparingly soluble crystalline compounds, in particular, crystalline sulfides and halides of various metals (AgCl, Ag2S, Agl; PbS, etc.), are used to obtain more accurate results. During the cathode polarization of these electrodes in aqueous solutions, metal ions entering the crystal lattice of the electrode are reduced to metal, and the anion in a certain range of current densities goes into solution. In this way, it is possible to obtain a source of anions capable of forming insoluble compounds with metal ions. In this case, titration is performed by potentiometric method. of course, and the amount of ion generated is precipitated by the amount of electricity passed through the electrolyzer.

The drawing shows a diagram of an electrolytic cell designed to generate precipitator ions.

The proposed electrolyzer is made entirely of organic glass and consists of a housing 1 in which a conical ground tube 2 is inserted from the bottom with a crystal cathode 3 mounted on the end of the tube using self-hardening plastic. In the upper part of housing 1, a cellophane diaphragm 4 and anode chamber 5 are installed, and a seal between housing 1, diaphragm 4 and chamber 5 is achieved. By means of a gasket 6. The anode space inside chamber 5 is filled with solution K, into which anode 7IZ is placed. platinum. In the space between the cathode 3 and the diaphragm 4, with a volume of about 0.2 ml, an indifferent electrolyte continuously flows through the capillary tubes 8 and 9.

During the analysis, an indifferent electrolyte, for example, from a Marriott flask enters the electrolyzer and enriched with chlorine, sulfur or other elements enters the titration vessel containing the analyzed solution. The constant current for generation is taken from the CT-1 electronic current stabilizer and set in a milliammeter; at the same time, simultaneously with the polarizing circuit, the toggle switch is turned on. The amount of electricity spent on the generation of precipitator ions is determined using an H370 type current integrator connected in series with a milliammeter.

Example. The definition of silver.

The analysis of silver ions is carried out in pure solutions by precipitation as sulphides. The generation of sulfur ions is made from an electrode made from fused silver sulfide at a current density of 0.2 a / dz. The end point of the titration is determined potentiometrically with an indicator sulfide silver electrode. The reference electrode is a calomel electrode. The connecting bridge is filled with KNOs. Measurement of emf It is produced by a PPTV1 potentiometer (see drawing), the M91 galvanometer of the type a / dz serves as a null instrument. The data obtained are shown in the table.

An even higher accuracy of determination was achieved when determining mercury ions in an acidic medium using a modified Photec method with cathodic polarization of an electrode made of fused silver chloride and determining the exact end of the titration with a colorimetrically shifted indicator (bromophenol blue and diphenylcarbazide alcohol solution).

Subject invention

The method of coulometric analysis of metals by deposition, which is characterized by the fact that, in order to obtain more accurate results, generator electrodes made of insoluble crystalline compounds are used.