SU1137377A1 - Method of determining variable-valence metal cations - Google Patents

Abstract

METHOD FOR DETERMINATION OF CEMENTS OF iMETAfmOB VARIABLE VALENCE, including their reduction with acetone in an acidic medium and subsequent quantitative registration using a redox reaction, characterized in that, in order to expand the possibility of separate determination of copper (II), cobalt (III), manganese (III) and nickel (III) in the presence of iron (II), the process of reducing wasps with a grit at a ratio of cation / in the sample and acetone of 1-, 3-2.8 and pH of 3.5-4.5, and as an oxidation-reduction reactions used- oxidation of excess acetone with iodine is observed.

Description

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The invention relates to analytical chemistry, namely, methods for determining variable-valence metal cations by reduction with acetone in an acidic medium in objects of complex composition. Methods are known for determining manganese by titrating the test solutions with reducing agents. A disadvantage of the known methods is the impossibility of determining manganese when co-present in objects of complex composition. The closest to the invention to the technical essence and the achieved result is the method of determining metal cations of variable valence, including their reduction with acetone in an acidic medium, oxidation with a solution of potassium dichromate and subsequent titration of excess potassium dichromate with a solution of salt Mora 2 However, the known method is applicable only to determine manganese ( III has a narrow measurement range (for ratios of manganese (III) and iron (II), equal to 0.2-0.5: 1.0), is complex, in hardware design and requires a duration of anal in about 5 hours. The aim of the invention is to expand the possibility of separate determination of copper (II), cobalt (III), manganese (III) and nickel (III) in the presence of iron (II). This goal is achieved by the proposed method for the determination of metal cations of variable valence, including restoration of them with acetone in an acidic medium at the ratio of the scientific research institute of the initial sample of cation and acetone 1-2.3-2.8 at pH 3.5-4.5 and subsequent quantitative registration using the oxidation reaction of excess acetone with iodine. ;. ,, .. in the table. Figure 1 shows the dependences of the reaction time of the reduction of Mn (lII) with acetone on the pH of the medium. YIO the following oxidation of excess acetone with iodine and the determination of excess iodine make it possible to determine the amount of acetone that entered into the reduction reaction with the cation under study, and iodine is chosen as the acetone oxidant because the reaction with it in an acidic medium proceeds quickly and completely without additional accelerators or catalysts, since acetone is already present in the desired enol form and using the same apparatus as in the reduction process. Example 1. Determination of copper (II) in the presence of iron (II) in acidic solutions. 20 ml of the test solution containing copper (II) ions in the amount of O, -0300-0.5000 g-ion / l, and iron (II) in the amount of 0.01000, 3000 g-ion / l (at a ratio of 0.20 : 1.01), placed in a 100 ml measuring flask, 2 ml of acetone (copper (II): acetone. 10-2.3) are added, since in terms of the maximum copper (II) content. In a 20 ml solution 0,0117 g-ion / l is present, then the required volume is 0,0177 k2.3-58.08: 0, 978 ml of ct2 ml, the pH is adjusted to 4.5 with 2 n. sulfuric acid and add water to the mark. Next, the mixture is transferred to a round bottom flask equipped with a reflux condenser and thermostatic for 0.25 h, 20 ml 0.05 N are introduced. iodine and thermostat solution at the same temperature for another half hour, the solution is cooled and the excess iodine is determined by potentiometric titration with sodium thiosulfate solution. 10.15 ml of 0.01 N was used to titrate the excess iodine. sodium thiosulfate solution Iodine was added to 0.1269 g (20 ml of 0.05 N solution), therefore, from the equation of the oxidation of iodine it is easy to calculate that 0.101 g of iodine was reacted with an excess of acetone (according to the reaction equation iodine and acetone) 0.2312 g of acetone. This means that 1.3288 g of acetone was spent on the copper (II) reduction reaction, which corresponds to the recovery of 0.7274 g of copper (II) to copper (I) in accordance with the reduction reaction equation. The concentration of copper (II) in the initial solution is 0.46 g-ion / l. If necessary, determination of the iron (II) content is carried out by any known method, for example, by potentiometric titration with potassium bichromate.

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So, for the titration of the sample 20 ml went to 3.6 ml 0.02 n. potassium dichromate solution, which corresponds to 0.0041 g of iron (II), i.e. its concentration in a solution of 0.2050 g-ion /

Example 2. Determination of cobalt (III) in the presence of iron (II) in acidic solutions.

20 ml of the test solution containing cobalt (III) ions in the amount of 0.5000-1.300 g-ion / l and iron (II) in the amount of 0.01000, 300 g-ion / l (ratio of cobalt (111): iron (11 ) 5.0: 1.0) is placed in a 100 ml volumetric flask, 5 ml of acetone is added (cobalt (III): acetone ratio is 1: 2.5), since, based on the maximum amount of cobalt ions in a 20 ml solution 0.0266 g-ion / l of acetone will require 5 ml. The pH of the medium is adjusted to 3.5 with the addition of 2N. sulfuric acid and add water to the mark ..

Next, the mixture is transferred to a round bottom flask equipped with a reflux condenser and thermostatic at 0.25 h, then 20 MF 0.05 n, iodine solution is introduced and thermostatic at the same temperature for another half hour. The solution is cooled and an excess of iodine is determined by potentiometric titration with 0.01 N, sodium thiosulfate solution. 18.95 went to titration, which corresponds to 0.0470 g of reagent. Using the calculation method used in Example 1, we obtain 0.8621 g-ion / l of cobalt (III) given 3773774

the concentration enters a definable interval.

PRI me R 3. Determination of nickel (III) in the presence of iron (II) 5 in acidic solutions.

20 ml of the test solution containing nickel (III) ions in the amount of 0.0700-0.0100 g-ion / l and iron (II) in the amount of 0.01000, ZSO g-ion / l (ratio of nickel (III): iron (Ii) 1: 1, placed in a 100 ml volumetric flask, 1.3 ml of acetone (atetok: nickel (III) 2.8: 1.0) added, calculated on the maximum nickel (III) content, adjusted to pH medium to 4.0 with addition of 2N sulfuric acid, topped up with water up to the mark.

On the titration of excess iodine went 2.5 MP 0.01 n. sodium thiosulfate. The calculated amount of nickel (III) ion was 0.0923 g-ion / l, this concentration falls within a defined interval.

A comparison of the accuracy of the known and proposed methods for determining the content of manganese (III) cations in the presence of iron (II) is given in Table. 2

As follows from the table. 2, the proposed method expands the range of measured concentrations of Mn (lH): Fe (lI) from 0.2: 1.0 - 0.5: 1.0 to 0.2: 1.0 - 5.0 by a factor of 10 : 1.0 with preservation of sufficiently high accuracy of analysis (relative measurement error of 1.8%)

1.5 2.5 3.5 4.5 5.0

0.57 0.96 0.90 0.25 0.28 0.88 1.05

Table 1

6.0 7.0 1.12 Does not go

table 2

Claims (1)

METHOD FOR DETERMINING CATION (METALS OF VARIABLE VALENCY, including their reduction with acetone in an acidic medium and subsequent quantitative registration using a redox reaction, characterized in that, in order to expand the possibility of separate determination of copper (II), cobalt (III), manganese (III ) and nickel (III) in the presence of iron (II), the reduction process is carried out at a ratio of cation / in the sample and acetone 1 - ^, 3-2.8 and the pH of the medium 3.5-4.5, and as the oxidation reduction reaction using-> cause the oxidation of excess acetone by iodine.