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ПОТЕНЦИОМЕТРИЧЕСКОЕ ОПРЕДЕЛЕНИЕ “АКТИВНОГО ХЛОРА” В ЭЛЕКТРОХИМИЧЕСКИ ОБРАБОТАННЫХ ХЛОРИДСОДЕРЖАЩИХ ЭЛЕКТРОЛИТАХ

Научная статья
Баранова Е.И.
Выскубова Е.Н.
Бажина Т.П.
DOI:
https://doi.org/10.23670/IRJ.2017.66.189
Выпуск: № 12 (66), 2017
Опубликована:
2017/12/18
PDF

Баранова Е.И.1, Выскубова Е.Н.2, Бажина Т.П.3

1Кандидат химических наук, доцент, 2кандидат химических наук, 3кандидат технических наук

ФГБОУ ВО «Кубанский государственный технологический университет», Краснодар, Россия

ПОТЕНЦИОМЕТРИЧЕСКОЕ ОПРЕДЕЛЕНИЕ “АКТИВНОГО ХЛОРА” В ЭЛЕКТРОХИМИЧЕСКИ ОБРАБОТАННЫХ ХЛОРИДСОДЕРЖАЩИХ ЭЛЕКТРОЛИТАХ

Аннотация

Основная часть анализов остаточного активного хлора выполняется традиционным химическим методом, в основе которого – методика объемного титрования рабочим раствором тиосульфата натрия с визуальной индикацией точки эквивалентности по крахмалу. Главными недостатками методики являются малая химическая устойчивость растворов тиосульфата натрия, необходимость периодической проверки его титра, высокий предел определяемых содержаний активного хлора и соответственно низкая чувствительность метода, относительно большая ошибка определения. С целью устранения указанных недостатков объемного классического анализа, автоматизации метода, сокращения его трудоемкости проводятся исследования по разработке инструментальных методов контроля активного хлора. Предложен вариант косвенного потенциометрического метода определения общего содержания “активного хлора” в электрохимически обработанных хлоридсодержащих электролитах без применения буферной системы.

Ключевые слова: электрохимическая обработка, хлорид натрия, окислительно-восстановительный потенциал.

Baranova E.I.1, Vyskubova E.N.2 Bazhina T.P.3

1PhD, Associate Professor, 2PhD,3 PhD

FGBOU VO "Kuban state technological university", Krasnodar, Krasnodar, Russia

POTENTIOMETRIC DETERMINATION OF “AVAILABLE CHLORINE” IN ELECTROCHEMICALLY TREATED CHLORINATED ELECTROLYTES

Abstract

The most of analyses of residual available chlorine are carried out by traditional chemical technique based in the methods of volumetric titration by means of working solution of sodium thiosulphate with visual indication of equivalence point on starch. The main disadvantages of the methods are low chemical stability of sodium thiosulphate solutions, necessity of periodic control of titre, high limit of available chlorine content and therefore low sensitivity of the technique and relatively significant error of determination. That research work on developing instrumental methods of available chlorine control is carried out. Its purpose is to eliminate the disadvantages of classic volumetric analysis, to automatize it and reduce labour intensity. Variant of indirect potentiometric method for determination of total content of active chlorine in electrochemically treated electrolytes, containing chlorine, without the use of a buffer system proposed.

Keywords: Electrochemical processing, sodium chloride, redox potential.

Introduction

The water for different application is disinfected by chlorine to provide sanitary, hygienic indices of drinking, household, technical water, technological liquids and to solve environmental problems. During the last years and today in water purifying installations (both in Russia and other countries), liquefied chlorine for disinfection of water is being replaced by the other analogous methods that are more simplified and rather safe. According to our data and data obtained by the scientists of developed countries, the most promising way of disinfection of water is electrolytic sodium hypochlorite treatment. The basis of the technique is electrolysis of water solution of sodium chloride in flowing condition.

Control of residual available chlorine is obligatory after chlorination. The term of “available chlorine” means total content of strong chlorinated oxidants in water i.e. sodium hypochlorite, molecular dissolved chlorine and chloramines. The most of analyses of residual available chlorine are carried out by traditional chemical technique based in the methods of volumetric titration by means of working solution of sodium thiosulphate with visual indication of equivalence point on starch. The main disadvantages of the methods are low chemical stability of sodium thiosulphate solutions, necessity of periodic control of titre, high limit of available chlorine content and therefore low sensitivity of the technique and relatively significant error of determination [1, P. 224]. Systematic error of iodide-starch methods is about 8 relative % at CAch = 0.3-0.7 mg/l and it is reduced to 4 relative % at CAch = 1.5 mg/l. It is known that research work on developing instrumental methods of available chlorine control is carried out. Its purpose is to eliminate the disadvantages of classic volumetric analysis, to automatize it and reduce labour intensity.

Electrochemical and especially anodic treatment (activation) is widly used for sample preparation in algorithm of various electrochemical and other physics-chemical methods of analysis [2, P. 11].

The purpose of the paper is to develop the technique of determination of available chlorine in electrochemically treated liquid by indirect potentiometric method.

Experimental

Electrochemical generation of available chlorine in sodium chloride solution (salt content is from 0.001 to 1.0 mole/dm3) was carried out in anodic chamber of two-chamber flowing electrolyzer with electrodes in the from of graphite disks. The experiment was made in condition of direct and pulse current (from 0.05 to 0.5 A; the interval of current density was from 8 to 70 A/m2). Formation of oxidation-reduction potential was controlled with potentiometric measurements (indicator-point-platinum electrode ЭПВ-1, chloride-silver reference electrode ЭВЛ 1 М3) in both anolyte flow and a sampler at mixing by means of magnetic mixer. A fragment of anolyte forms galvanic cell.

Results and Discussion

 Analytical control of available chlorine content ( mAch or CAch, mg/dm3 or mole/dm3) in electrochemically treated liquid (i.e. in anolyte) was carried out by iodometric titration technique with visual indication of the end point of titration according to ГОСТ 18190-72 [3, P. 3-6]. Unlike the standard methods we selected several times smaller volume of liquid sample to analyze.

Methods of determination of available chlorine by volume iodometric titration.

0.5-1.0 of dry potassium iodide is put into conic retort of 100 cm3, it is dissolved in 1-2 cm3 of distilled water, then 1 cm3 of buffer solution with pH = 4.5 and 25 cm3 of anolyte or proper model solution is added. Isolated iodine is titrated by means of thiosulfate solution of С(Na2S2O3) = 0.005 mole/dm3 concentration up to light-yellow colour. Then 1 cm3 of 0.5 % starch solution is added and titrated until blue colour disappears.

Mass fraction of available chlorine (mAch, mg/dm3) is calculated according to the formula

15-02-2018 13-24-31                                                                     (1)

 15-02-2018 13-25-38- the quantity of 0.005 (normal) sodium thiosulfate solution used for titration, cm3;

К – coefficient of correction of sodium thiosulfate solution normality;

0.177 – available chlorine content that is equivalent to 1 cm3 of 0.005 N sodium thiosulfate solution;

V – the volume of water sample selected for the analysis, cm3;

1000 – conversion coefficient to converse gramme of mass into milligramme.

Molar concentration of available chlorine in anolyte (CAch, mole/dm3) is calculated according to the formula

15-02-2018 13-26-14                                                             (2)

 15-02-2018 13-25-38- total volume of 15-02-2018 13-27-48used for titration (up to the end point of titration), cm3;

Vx – volume of anolyte for one analysis, cm3.

The other method of quantity determination of available chlorine in electrochemically treated solution (i.e. in anolute) with various content of sodium chloride is indirect potentiometric method without titration (one-point oxidation-reduction titration), based on measurement of two values of oxidation-reduction potential 15-02-2018 13-28-21 in reversible (balance) electrochemical iodine-iodide system with Pt-indicator electrode: after mixing the sample and reagent (KI) – (E1) and after adding the dose of standard (fiksanalny) solution of iodine (E2). Primary isolation in the mix tested (E1) is conditioned by the reaction of available chlorine (oxidizer) with iodide-ions [4, P. 24], [5, P. 1951].

Various techniques of similar determination for control of residual quantity of available chlorine in drinking, industrial water and sewage, have been published. Apparently, potentiometric determination of available chlorine in electrochemically treated chlorinated electrolytes on the base of potentials 15-02-2018 13-28-21 have never been carried out. Fs it was mentioned above, reversible potentials 15-02-2018 13-28-21 are an important characteristic of oxidation-reduction properties of electrochemically treated liquid [6, P. 1739], [7, P. 30].

According to the theoretical analysis in the previous works [8, P. 724-726] the following dominating volumetric equilibrium reaction proceed in I2 – KI – NaCl system:

              15-02-2018 13-31-53                           (3)

15-02-2018 13-32-32               (4)

Electrochemical reactions are localized on the surface of platinum electrode:

15-02-2018 13-34-07                                     (5)

15-02-2018 13-34-53                                    (6)

15-02-2018 13-38-49   (7)

In the experimental conditions iodine is separated at considerable surplus of NaCl and KI, thus it is possible to describe concentration of iodine C(I2) in the tested solution

С(I2) = [I2] + [I3-] + [I2Cl-]                     (8)

In consideration of equilibrium of all reactions (3-7) we can describe oxidation-reduction potential of the studied system in the terms of Nernst equation for electrochemical reaction (6). Expressing the concentration [I3-] from the equation (8) at

15-02-2018 13-40-44                                            (9)

15-02-2018 13-41-59                                    (10)

we can obtain

15-02-2018 13-46-59        (11)

 15-02-2018 13-48-24- formal potential of the reaction (6);

15-02-2018 13-48-55 - concentration constant of formation of 15-02-2018 13-49-23 [9, P. 1459];

 15-02-2018 13-50-05- concentration constant of formation of I2Cl particle [9, P. 1461].

Taking into consideration relatively high ionic strength of the tested solution from the equation (11)

We can obtain

15-02-2018 13-50-35                     (12)

The correlation (12) agree with experimental data: experimental dependence of electromotive force of voltic cell on 15-02-2018 13-51-34is linear and it is withing the range C(I2) = 2. 0-4 – 1. 0-2 mole/dm3. Therefore, the average experimental value of the slope of the electrode function is S = 29.9 mV. The results obtained confirm that it is possible to use indirect potentiometric method of determination of available chlorine without titration in electrochemically treated salt solution.

Methods of determination of available chlorine in electrochemically treated liquid by indirect potentiometric technique. 50 cm3 of anolyte solution is put into a beaker of 100 cm3, then 0.5 g of dry potassium iodide is added and dissolved; the firs value of oxidation-reduction potential E1 is measured. Then 1 cm3 additive of standard (fiksanalny) solution of iodine of C(I2) = 0.1 mole/dm3 concentration is put in and the second value of oxidation-reduction potential E2 is measured. The difference of potentials

15-02-2018 13-52-34                                                      (13)

The content of available chlotine CAch, mole/dm3 is calculated by means of the formula

15-02-2018 13-53-46                                                  (14)

C(I2) – concentration of fiksanalny solution of iodine mle/dm3;

15-02-2018 13-54-29 - the volume of standard iodine additive, cm3

Vx – the volume of anolyte for one experiment, cm3;

S – the slope of the electrode function, mV.

CAch is multiplied by 0.0355 to evaluate the content of available chlorine according to mass fraction mAch, mg/dm3.

The results of available chlorine determination in analyte of flowing two-chamber electrolyzer at various modes of electrolysis by iodometric titration and indirect potentiometric techniques are shown in tables 1 and 2.

The obtained results15-02-2018 13-55-08 are considered to be quite reliable as there is satisfactory accordance between techniques of iodometric titration and indirect potentiometry: more then half results of anolyte samples by criterion F in tables 1 and 2; by t-criterion it has been established almost complete absence of significative systematic error [10. P. 47].

Table 1 –  The results determination of available chlorine mass fraction in the anolyte samples of flowing two-chamber electrolyzer by iodometric titration method (n=3; P=0.95; tp=4.30)

15-02-2018 13-56-24

Table 2 – The results of determination of available chlorine mass fraction in anolyte samples of flowing two-chamber electrolyzer by the method of indirect potentiometry (without titration). The conditions of electrolysis – see table 1 (n=3; P=0.95; F(P,f1,f2)=19.00; tp=4.30

15-02-2018 13-57-26

At 15-02-2018 13-58-50= 19.00 the value of t-criterion is using the formula

15-02-2018 13-59-33                                     (15)

n1=n2=3, C1 and C2 are average values of15-02-2018 13-55-08 according to the results of chemical and electrochemical analysis.

At15-02-2018 13-58-50= 19,00 the value of t-criterion is using the formula

15-02-2018 14-01-51                                                          (16)

taking into account that the results of chemical analysis C2 are the nearest tj the true value of m(ACh) concentration [10. P. 60]. According to tables 1 and 2 the conditions of electrolysis (amperage, velocity of electrolyte current) do not influence sensitively the results of determination of CAch.

Conclusions

Suggested in the paper variant of indirect potentiometric method of total content determination of available chlorine without using buffer system leads to quite reliable data about CAch in electrochemically (by anode) treated chlorinated water solutions with pH about 1.5 – 3.5 (HCl formation).

The method can be used by control-analytical services that makes it possible to reduce labour intensity of the analysis of residual available chlorine determination and to enhance its sensibility.

Список литературы / Reference

  1. Determination of chlorine oxides by amperometric titrator using current-integration method / Watanabe T., Tanaka M., Shu-ming Chen, et al // Bunseki Kagaku. – 1991. – Vol.40, № 12. – P.221-226.
  2. Svintsova L.D., Chernyshova N.N. Sample preparation by electrochemical pretreatment in the membranous electrolyzer // Int. Congress on Analyt. Chem.: Abstracts / Moscow. St. Univ. – M., 1997. – Vol.1. – P.10-12.
  3. ГОСТ 18190-72. Вода питьевая. Методы определения содержания остаточного активного хлора.– Введ. 1974-01-01. – М.: Изд-во стандартов, 2010. – 12 с.
  4. Сериков Ю.А. Потенциометрическое определение активного хлора в промышленных и сточных водах титаномагниевого производства / Ю.А. Сериков, Т.В. Носкова // Заводская лаборатория. – 1988. – № 7. – С.23-26.
  5. Власов М.Ю Потенциометрическое определение остаточного активного хлора / М.Ю. Власов, Ю.И. Николаев, А.М. Писаревский и др. // Журнал прикладной химии, 1984. – Т.57, № 9. – С.1949-1954.
  6. Писаревский А.М. Потенциометрическое определение активного хлора с использованием кулонометрического введения стандартной добавки иода / А.М. Писаревский,  Ю.А. Сериков, Т.Д. Шигаева и др. // Журнал прикладной химии, 1986. – Т.59,  № 8. – С.1737-1743.
  7. Писаревский А.М. Возможности потенциометрической методики определения остаточного активного хлора в питьевой воде / А.М. Писаревский, И.П. Полозова, Ю.И. Николаев и др. // Вестник СПбГУ. Сер.4. – 1992. – Т.1, № 4. – С.29-35.
  8. Турьян Я.И. Окислительно-восстановительные процессы в системе I2+KI+NaCl и потенциометрическое определение иодида калия в поваренной соли / Я.И. Турьян, Л.М. Малука, Т.Р. Маркова // Журнал аналитической химии. – 1992. – Т.47, № 4. – С.723-730.
  9. Турьян Я.И. Косвенное редокс-потенциометрическое определение меди / Я.И. Турьян, Л.М. Малука, Т.Р. Маркова // Журнал аналитической химии. – 1992. – Т.47, № 8. – С.1456-1463.
  10. Дерффель К. Статистика в аналитической химии / Пер. с нем. – М.: Мир, 1994. 268с.

Список литературы на английском языке / References in English

  1. Determination of chlorine oxides by amperometric titrator using current-integration method / Watanabe T., Tanaka M., Shu-ming Chen, et al // Bunseki Kagaku. – 1991. – Vol.40, № 12. – P.221-226.
  2. Svintsova L.D.,Chernyshova N.N. Sample preparation by electrochemical pretreatment in the membranous electrolyzer // Int. Congress on Analyt. Chem.: Abstracts / Moscow. St. Univ. – M., 1997. – Vol.1. – P.10-12.
  3. GOST 18190-72. Voda pit'evaja. Metody opredelenija soderzhanija ostatochnogo aktivnogo hlora. [Drinking water. Methods for determining the content of residual active chlorine]. Vved.1974-01-01. – M.: Izd-vo standartov, 2010. - 12 p.[in Russian]
  4. Serikov U.A. Potenciometricheskoe opredelenie aktivnogo hlora v promyshlennyh i stochnyh vodah titanomagnievogo proizvodstva [Potentiometric determination of available chlorine in industrial water and sewage of titanium-magnesium production] / U.A.Serikov, T.V. Noskova // Zavodskaja laboratorija [Laboratory Manager]. – 1988. – № 7. – P.23 - 26. [in Russian]
  5. Vlasov M.Ju. Potenciometricheskoe opredelenie ostatochnogo aktivnogo hlora [Potentiometric determination of residual active chlorine] / M.Yu.Vlasov, Yu.I.Nikolayev, A.M. Pisarevsky and others // Zhurnal prikladnoj himii [Journal of Applied Chemistry]. – – Vol. 57, №. 9. –  P.1949-1954. [in Russian]
  6. Pisarevskij A.M. Potenciometricheskoe opredelenie aktivnogo hlora s ispol'zovaniem kulonometricheskogo vvedenija standartnoj dobavki ioda [Potentiometric determination of active chlorine using coulometric injection of a standard iodine supplement] / A.M.Pisarevskij, Yu.A.Serikov, Т.D. Shigaeva and others // Zhurnal prikladnoj himii [Journal of Applied Chemistry]. – Vol. 59, №. 8. –  P.1737-1743. [in Russian]
  7. Pisarevskij A.M. Vozmozhnosti potenciometricheskoj metodiki opredelenija ostatochnogo aktivnogo hlora v pit'evoj vode [Possibilities of potentiometric technique for determination of residual active chlorine in drinking water] / A.M.Pisarevskij, I.P. Polozova, Yu.I. Nikolaev and others // Vestnik SPbGU. Serija 4 [Bulletin of St. Petersburg State University. Series 4]. – – Vol. 1, №. 4. –  P.29-35. [in Russian]
  8. Turyan A.I. Okislitel'no-vosstanovitel'nye processy v sisteme I2+KI+NaCl i potenciometricheskoe opredelenie iodida kalija v povarennoj soli [Oxidation-reduction processes in the system I2+KI+NaCl and potentiometric determination of potassium iodide in sodium chloride] / A.I.Turyan, L.M. Maluka, T.R. Markova // Zhurnal analiticheskoj himii [Analytical chemistry journal]. – 1992. – Vol.47, №4. – P. 723-730. [in Russian]
  9. Turyan A.I. Kosvennoe redoks-potenciometricheskoe opredelenie medi [Indirect redox-potentiometric determination of copper] / A.I.Turyan, L.M. Maluka, T.R. Markova // Zhurnal analiticheskoj himii [Analytical chemistry journal]. – 1992. – Vol.47, №8. – P. 1456-1463. [in Russian]
  10. Doerfel K. Statistics in analytical chemistry / Transl. from German. – М.:Mir, 1969. - 248 p.