A Titration Method for Meas Measur urin ing g Chlo Chlora rate te Ion Ion in Concentrated Bleach Solutions
3n m9todo de aloraci:n para medir iones clorato en soluciones blanqueadoras concentradas
The minimization of bleach loss is a high priority for sodium hypochlorite producers. The largest source of bleach loss during production is process related with the subsequent formation of chlorate ion.
7a minimizaci:n de la p9rdida de cloro es una alta prioridad para los productores de hipoclorito de sodio. sodio. 7a m;s grande grande fuente fuente de p9rdid p9rdida a de cloro cloro durante su producci:n es el proceso relacionado con la consec consecuen uente te formac formaci:n i:n de iones iones clorat clorato. o.
The most accurate measurement method for determining the chlorate ion concentration in bleach is ion chromatography (IC). Because this measurement requires specialized equipment and training, most bleach producers are unable to measure the chlorate ion concentration (and the subsequent bleach loss) at the production site. Thus, a titration method has been deeloped for on!site use to estimate the chlorate ion concentration in "#!"$% bleach solutions.
a es la cromatograf>a i:nica (CI). ?ebido a que esta esta medi medida da requ requie iere re equi equipo po espe especi cial aliz izad ado o y entrenamiento, la mayor>a de los productores de blan blanqu quea eado dore ress son son incap ncapac aces es de medir edir la concentraci:n de iones de cloruro (y la posterior p9rdida p9rdida de cloro) en la zona de producci:n. producci:n. @or lo tanto, un m9todo de aloraci:n ha sido desarrollado para su uso en el sitio para estimar la concentraci:n de iones de cloruro en las soluciones de cloro "#!"$%.
The titration method is based on the method proposed by &ieta, 'oberts and ernandez (&**&,"+-, (&**&,"+-, /(")0/-). The bleach sample is prepared by remoing the aailable chlorine by reaction with hydrogen pero1ide. The measurement is based on the titration of iodine by sodium thiosulfate. &t p 2, a number of o1idizing species in the sample are titrated (e.g. chlorite ion). 3nder highly acidic conditions, chlorate ion is titrated along with the o1idizing species titrated at p 2. The chlorate ion concentration is calculated by ta4ing the difference of the titrations.
a se prep prepar ara a medi median ante te la elim elimin inac aci: i:n n del del clor cloro o por por reacci:n con per:1ido de hidr:geno. 7a medici:n se basa en la aloraci:n de yodo para el tiosulfato de sodio. & p 2, un nAmero de o1idaci:n las especi especies es de la muestr muestra a se alora alora (por (por e=empl e=emplo o ione ioness de clor cloritito) o).. Ba=o Ba=o cond condic icio ione ness alta altame ment nte e ;cid ;cidas as,, el ion ion clor clorat ato o se alo alora ra =unt =unto o con con las las especies o1idantes aloradas a p 2. 7a concentraci:n del ion clorato se calcula tomando la diferencia de las aloraciones.
This method is to be used for chlorate ion concentrations between ",### 5 "#,### mg67. Chemistry Background
The pertinent chemistry for this method is 8!fold0
7a qu>mica pertinente para este m9todo consiste en tres pasos0
") the remoal of chlorine 2) reactions at p 2
") la eliminaci:n del cloro 2) las reacciones a p 2 sensibilidad
8) reactions under ery acidic conditions.
8) 'eacci:n ba=o condiciones muy ;cidas.
Chlorine is remoed by treating the bleach sample with hydrogen pero1ide as shown below0
Cl2 2 ! D 2Cl! 2 2 This step remoes chlorine as a potential interference in the method. &s hydrogen pero1ide reacts with EI to form iodine, the treated sample is heated to remoe any residual hydrogen pero1ide. &t p 2, any number of o1yhalogen species that might be present in bleach solutions can react with EI. Thus it is important to account for the presence of these species in the final calculation. For e1ample, chlorite ion (Cl 2 !)0 Cl2! -I! - D 2I2 Cl! 22
Chlorite ion is a steady!state intermediate species that is formed when bleach decomposes !! 2 hypochlorite ions react to form chlorite ion0
Iones de clorito es una especie de estado estacionario intermedio que se forma cuando el cloro se descompone 5 2 iones hipoclorito reaccionan para formar iones de clorito0
Cl! Cl! D Cl2! Cl!
Cl! Cl! D Cl2! Cl!
This means that for eery GmoleH of chlorite ion present in bleach, 2 GmolesH of hypochlorite ion are lost. &s an intermediate species, chlorite ion will readily react with hypochlorite ion to form chlorate ion0 Cl2 ! Cl! D Cl8 ! Cl! This means that for eery GmoleH of chlorate ion present in bleach, 8 GmolesH of hypochlorite ion are lost !!! thus, a high concentration of chlorate ion might represent a substantial bleach loss. 3nder ery acidic conditions, chlorate ion reacts with iodide ion to form iodine
a, 8 moles de ion hipoclorito se !!! perdido por lo tanto, una alta concentraci:n de iones de cloruro podr>a representar una p9rdida de cloro sustancial.
Cl8! /I! / D 8I2 Cl! 82
& difficulty that can present itself under highly acidic reaction conditions is the o1idation of iodide
Cl8! /I! / D 8I2 Cl! 82 3na dificultad que puede presentarse en condiciones de reacci:n muy ;cida es la o1idaci:n
ion to iodine resulting in a positie bias. To minimize this potential problem, bromide ion is used as the reducing agent. Bromide ion is not o1idized by o1ygen under these conditions. &fter the reaction is completed (2# min), iodide ion is added to the sample and iodine is formed following reaction with bromine resulting from the reduction of the chlorine species originally present in the sample. 'apid dilution of the sample with sodium phosphate lowers the acidity of the sample thus minimizing unwanted side reactions.
del ion yoduro al yodo que resulta en un sesgo positio. @ara minimizar este problema potencial, el ion bromuro se utiliza como agente reductor. Ion bromuro no se o1ida con el o1>geno ba=o estas condiciones. ?espu9s de la reacci:n es completada (2# min), ion yoduro se agrega a la muestra y el yodo se forman despu9s de la reacci:n con bromo resultante de la reducci:n de las especies de cloro originalmente presentes en la muestra. ';pido diluci:n de la muestra con fosfato de sodio reduce la acidez de la muestra lo cual reduce reacciones secundarias no deseadas.
Sample Preparation
The following laboratory equipment6chemicals are required0 "## m7 olumetric flas4 8#% ydrogen @ero1ide 2# m7 pipette Jtir bar eated Jtir @late $m7 disposable plastic pipette ". &ccurately pipette 2# m7 of the concentrated bleach sample into a "## m7 olumetric flas4 2. @lace the olumetric flas4 on the heated stir plate and place the stir bar in the flas4 8. Turn on the stir plate so that the stir bar reoles in a controlled manner -. 3sing the $ m7 plastic pipette, slowly and carefully add the hydrogen pero1ide. CAUTIO! The addition of hydrogen pero"ide to #leach can #e a $iolent reaction% The addition must #e done slo&ly so that the e$olution of o"ygen is controlled and the reaction is contained in the $olumetric flask% 'hen the hydrogen pero"ide is added too (uickly) the reaction &ill *#u##le+out, of the flask% Appropriate eye&ear and protecti$e clothing must #e used at all times%
For "#!"$% bleach, e1pect to add -!/ m7 of 8#% hydrogen pero1ide. *hen the appropriate olume of hydrogen pero1ide has been added, the solution in the flas4 will turn colorless and the addition of hydrogen pero1ide will not generate o1ygen.
$. Turn the stir plate heater on and continue to stir the solution. &llow the solution to boil for "$
Preparaci-n de la muestra
micos son necesarios0 Katraz aforado de "## ml 8#% de per:1ido de hidr:geno 2# ml pipeta Barra de agitaci:n 'euela con calefacci:n mural $m7 pipeta de pl;stico desechable ". Tome con precisi:n 2# ml de la muestra de le=>a concentrada en un matraz aforado de "## ml 2. Colocar el matraz aforado en la placa agitadora con calefacci:n y colocar la barra de agitaci:n en el matraz 8. geno este controlada y la reacci:n est9 contenida en el matraz aforado. Cuando el per:1ido de hidr:geno se aNade tambi9n r;pidamente, la reacci:n ser; burbu=a! out del matraz. Oafas de protecci:n adecuadas y la ropa debe ser utilizado en todo momento. @ara blanqueador de "#!"$%, esperamos agregar -!/ m7 de per:1ido de hidr:geno al 8#%. Cuando el olumen adecuado de per:1ido de hidr:geno se ha aNadido, la soluci:n en el frasco a su ez, incolora y la adici:n de per:1ido de hidr:geno no a a generar o1>geno. $.
minutes in a controlled manner. /. 'emoe the flas4 from the hot plate and allow the solution to cool to room temperature. NOTE: &dding -# m7 of distilled water to the olumetric flas4 and placing the flas4 in an ice bath will speed up the cooling process. . 'emoe the stir bar and bring the solution to olume with distilled water.
agitando la soluci:n. ?e=e que la soluci:n ebulla durante "$ minutos de una manera controlada. /. 'etire el matraz de la placa caliente y de=e que la soluci:n se enfr>e a temperatura ambiente. MT&0 &gregar -# ml de agua destilada al matraz olum9trico y colocar el matraz en un baNo hielo acelerar; el proceso de enfriamiento. . 'etire la barra de agitaci:n y llear la soluci:n a olumen con agua destilada.
.easurements
The following laboratory equipment6chemicals are required0 "2$ m7
"## m7 olumetric flas4 and dilute to olume with distilled water. Jtore the solution in a brown glass! stoppered bottle. This solution should be made fresh daily. Hydrochloric Acid (2.5 N)0 Cautiously add 2# m7 of
concentrated Cl to $# m7 of distilled water with mi1ing in a "## m7 olumetric flas4 and dilute to olume.
.ediciones
drico conc "# ml pipeta (2) 2,$ M de ;cido clorh>drico Barra de agitaci:n fosfato de sodio 'euela mural tiosulfato de sodio $# ml Bureta Katraz aforado de "## ml (2) 2$ m7 probeta Preparar las siguientes soluciones!
Bromuro de potasio ($%)0 disoler $ g de EBr en un matraz aforado de "## ml y diluir a olumen con agua destilada. Conserar la soluci:n en una botella marr:n con tap:n de idrio.
Pcido clorh>drico (2,$ M)0 Cuidadosamente aNadir 2# ml de Cl concentrado a $# ml de agua destilada con la mezcla en un matraz aforado de Sodium hoshate (Saturated Solutio!) 0 @repare a "## ml y diluir a olumen. saturated solution of Ma 2@- "22 with cold distilled water (&dd enough sodium phosphate so o flas4). agua destilada (&Nadir suficiente sodio fosfato de Sta!dard Sodium Thiosul"ate (#.$ N) 0 This solution cristales para que M3!disueltos son obserables is typically aailable from chemical supply en el frasco). companies. *e recommend that this solution be purchased. If purchasing the prepared solution is picamente disponible de suministro dissole 2$ g Ma2J28 $2 in " 7 of freshly boiled de productos qu>micos las empresas. Je distilled water and standardize against potassium recomienda que esta soluci:n a a adquirirse. Ji la bi!iodate or potassium dichromate after at least a compra de la soluci:n preparada es two!wee4 storage. This initial storage is necessary no es posible, preparar la soluci:n de la siguiente
to allow o1idation of any bi!sulfite ion present. 3se boiled distilled water and add a few milliliters of chloroform to minimize bacterial decomposition.
Titration at p/ 0
". &dd " g of EI and "# m7 of distilled water to a "2$ m7
manera0 disoler 2$ g de Ma2J28 $2 en " 7 de reci9n herida agua destilada y estandarizar en contra de potasio o yodato bi!dicromato de potasio despu9s de al menos un de dos semanas de almacenamiento. nimo bacteriana descomposici:n. Titulaci-n a p/ 0
". &Nadir " g de EI y "# ml de agua destilada a un matraz de "2$ m7
". &dd " m7 of $%EBr and "# m7 of conc Cl to a "2$ m7 , el peso equialente de iones clorato se diide Mote0 M, normality, of the sodium thiosulfate (MTJ) por / para dar "8.+#+ mg6equialente. is #." M ($) is the dilution factor of the original solution !! 2# Cl8!(mg67) Q (&!B) (MTJ M) ("8.+#+) ($) m7 of bleach was diluted to "## m7
To conert to g67 MaCl 8 diide by "### and multiply by ".20
Mota0 M, normalidad, del tiosulfato de sodio (MTJ) es de #," M ($) es el factor de diluci:n de la soluci:n original ! 2# ml de le=>a se diluy: a "## ml
g67 MaCl8 Q (mg67 Cl8!) (".2 6",###) For eery " g67 of MaCl8, there is a loss of 2 g67 of aailable chlorine
@ara conertir en g67 MaCl8 diidir por "### y multiplicar por ",20 g67 MaCl8 Q (mg67 Cl8!) (",26".###)
NOTE: The method is to e used "or co!ce!tratio!s et&ee! $'### a!d $#'### m*. +" the calculated co!ce!tratio! e,ceeds $#'### m*' the reared samle should e diluted or a smaller samle si-e ealuated ("or e,amle' 5 m* i!stead o" 2# m*).
Jample ?ata (The & alues were calculated using a + m7 sample olume. The B alues were calculated using a 2# m7 sample olume) Jample Bleach S" & Q "./ 6 + Q #." Cl8 ! (mg67) Q (& 5 B) (M MTJ) ("8,+#+) ($) B Q #. 6 2# Q #.#8$ Cl 8 ! (mg67) Q (#." 5 #.#8$) (#.") ("8,+#+) ($) Q ++Titration alue0 ++IC alue0 +# "#+% agreement g67 MaCl8 Q (++-) (".2 6",###) Q ".2 Jample Bleach S2 & Q "8. 6 + Q ".$22 Cl8! (mg67) Q (& 5 B) (M MTJ) ("8,+#+) ($) B Q /.+ 6 2# Q #.8-$ Cl 8! (mg67) Q (".$22 5 #.8-$) (#.") ("8,+#+) ($) Q ,"$ Titration alue0 ,"$ IC alue0 ,+2% agreement g67 MaCl8 Q (,"$) (".2 6",###) Q "#.- MT<0 the aerage standard deiation of multiple titrations was less than
%$@or cada " g 6 7 de MaCl8, hay una p9rdida de 2 g67 de cloro disponible MT&0
g67 MaCl8 Q (,"$) (".2 6",###) Q "#.- MT<0 the aerage standard deiation of multiple titrations was less than
%$Gordon, G., Adam, L., Bubnis, B., 1995 “Minimizing Chlorate Ion Formation in rin!ing "ater "hen #$%o&hlorite Ion is the Chlorinating Agent', I(B) *+9-+1+5, Ameri&an "ater "or!s Asso&iation /esear&h Foundation, en0er, C determination o2 sodium &hlorate in sodium h$%o&hlorite solutions