International Journal of Chemical and Pharmaceutical Review and Research

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1 ISSN No: Int. J. Chem. Pharm. Rev. Res. Vol (2), Issue (1), 2015, Page Research Article International Journal of Chemical and Pharmaceutical Review and Research Is Estimation of Residual Free Chlorine in Water by Drop Number Titration Method Reliable? Investigation of Statistical, Pragmatic, Psychological and Philosophical reasons Shashi Chawla1, Renu Parashar2 and R.K.Parashar3* 1.Department of Applied Chemistry and Environmental Sciences, Amity School of Engineering & Technology, New Delhi. 2.Department of Chemistry, Hans Ra College, Delhi University, Delhi. 3.Department of Education in Science and Mathematics, NCERT, New Delhi, India. A R T I C L E I N F O Article history: Received 14 August 2015 Accepted 19 September 2015 Available online 24 September 2015 Keywords: Analytical Science, Potable water, Chemometrics, Statistical analysis, Residual free chlorine. A B S T R A C T Poor sanitation, rise in population of pathogenic microorganisms and lack of access to hygienic water are considered the main causes of water borne diseases. Chlorination is the most common disinfection process as it is capable of maintaining residual disinfecting properties and is less costly. Current methods used to monitor residual free chlorine require collection of a large volume of water, its transport to a testing laboratory, and its analysis using huge quantities of reagents which are found to be inconvenient and impractical in many parts of the world. To circumvent these limitations, we have developed and validated a method to measure residual free chlorine in water. The environmentally benign method involved the use of plastic Pasteur pipettes for delivery of desired number of drops. The data of estimated chlorine using the developed method from the 25 students were collected and statistical interpretation was done. The pragmatic, psychological and philosophical reasons were also explored for this method. The obtained results had good intermediate precision and accuracy. The main advantages of drop number titration method are less time required for analysis, energy savings, a drastic reduction of reagent consumption, and less waste generation. IJCPRR All rights reserved. 1. Introduction Judgment phase includes identification of the real-life problem (The need of water disinfection); selection of an appropriate objective (to test the disinfection processes); deciding the measures of effectiveness (accuracy and precision of the method) and the abstraction of the essential information so that a solution to the goals can be obtained. Operations research is concerned with scientifically deciding how to best design and operate man-machine systems that usually require the allocation of scarce resources. The operations research approach to problem solving is based on following three phases: Research phase includes a collection of observations and data analysis of the available information using preestablished measures of desirability and generalization of the result. The action phase consists of making recommendations for implementing the decision 1. Life is * Corresponding author. address: rkp.ncert@gmail.com Present address: Department of Education in Science and Mathematics, NCERT, New Delhi, India 11

2 impossible without water. It is essential for health, ecosystem services, economic development, and poverty reduction, protection of greenery, production of food and imparting of aesthetic beauty. The major factors responsible for water crisis in the world are growing population, better lifestyles, and pollution, and Climate change, spatial and temporal variations in available water. The most polluted are the Asian rivers in the world. They have twenty times more lead than rivers in industrialized countries and three times as many bacterias from human waste on a global average. About eighty percent of urban The environmental water quality has been modified by the wastes introduced into rivers, lakes, groundwater aquifers and the oceans by the human race. It also makes huge quantities of water unsuitable for various uses. According to NASA, October 2009, 20 th Century was the warmest century during in past 1000 years. Greenhouse gas emissions have produced significant changes in run-off and rainfall patterns. Population and consumption growth has increased water abstraction. Overharvesting and exploitation are the major cause of groundwater depletion and collapse of fisheries. Quality of water and supply of water is getting affected by these depletions of living resources and biodiversity. Often lack of access to hygienic water, poor sanitation and the rise in population of pathogenic microorganisms are considered the main causes of water borne diseases which are responsible for deaths of so many children and adults. The best ways to prevent waterborne diseases are to avoid drinking untreated water, to avoid consuming undercooked food, to educate for clean sanitation and to maintain good personal hygiene. Sustainability involves the management of water resources to increase long-term wealth and wellbeing for all 2. To limit the risk of disease transmission associated with potable water and wastewater, pathogenic organisms are waste ends up in the Indian rivers. Over three billion liters of raw sewage, industrial run-off and garbage are thrown into the Yamuna River every day. The Ganga River is also dying slowly due to unchecked pollution. Samples taken from the Ganga River near the Varanasi show that level of fecal coli form (a dangerous bacterium that comes from untreated sewage) was some three thousand percent higher than what is considered safe for bathing. The river water pollution is getting worse due to unchecked urban growth across the country combined with poor government oversight. efficiently eliminated from the water in the disinfection process. Boiling of water for treatments have the limitation that after application no residual chemical agent remains that can inactivate organisms that may be picked up throughout the distribution system, this disinfection is energy intensive and expensive, so its use is reserved for emergencies. Ozone is the most efficient disinfectant for the inactivation of bacteria, viruses and protozoa. Chlorination is the most common and low cost disinfection process. Moreover, it is capable of maintaining residual disinfecting properties. When chlorine gas is bubbled into water at near-neutral ph, it reacts rapidly to produce hypochlorous acid (the effective disinfecting agent). The optimum ph range for disinfectant application lies in the range 6 to 8, because the undissociated HOCl molecule is the most effective compound in the disinfecting process. Its efficiency is considered to be 80 times as high as that of the hypochlorite ion. Free chlorine is an effective disinfectant for bacteria and viruses, and compares well with the efficiency of ozone and chlorine dioxide for these microorganisms. However, it is less effective against Cryptosporidium parvum and Giardia lamblia than chlorine dioxide or ozone. Various disinfection processes are compared in Table 1. 3,4 Table 1: Comparison of the Disinfection Processes Disinfection Processes / Properties Boiling UV Irradiation Ozonization Chlorination Germicidal Potency Excellent Fair Best Very good Disinfection by-products No Not Known Yes, but limited Yes Cost Very high Not Known High Low Effective in distribution system No No No Yes Recommendations Use in emergency Use in home/offices Use in home/offices Use in the municipality 12

3 Disinfection of water by chlorination also helps in the almost complete removal of ammonium nitrogen. Hypochlorous acid is the effective chlorinating species under treatment conditions, and reacts with ammonium ion to form mono-, di-, and trichloramines. In the presence of carbon adsorption filters the chloroamines undergo a heterogeneous surface reaction that produces nitrogen gas as one of the products 5. Chlorination of water to the extent that all ammonia is converted to either trichloramine or oxidized to nitrogen or other gases is referred to as breakpoint chlorination. Free chlorine (HOCl and OCl - ) is the dominant disinfectant after the break point. Typically, the free chlorine residual is adjusted to maintain a minimum level of 0.2 ppm chlorine throughout the distribution system. The importance of break-point chlorination lies in the control of taste and odor and increased germicidal efficiency. The killing power of chlorine beyond break point is 25 times higher. Thus, the presence of free chlorine residual is an indicator of adequate disinfection 6. However, if the water contains natural organic matter (NOM) in the form of soluble humid material, chlorine / hypochlorous acid is able to chlorinate the terminal groups of the humate molecules and thereby produce small quantities of a series of trihalomethane compounds. The disinfection byproducts (DBPs) have been found to cause liver and bladder cancer in humans. The guideline values of recommended residual concentrations (in µg / L) for monochloramine, dichlorobromomethane and chloroform are 3000, 100 and 300 respectively 7. The aim is to use the smallest amount possible to fully disinfect, while avoiding the development of unpleasant taste, odor and the formation of undesirable compounds. A method used for the minimization of chlorine application is the measurement of the redox potential. The advantage of determining the redox potential lies in the fact that it gives information about the disinfective ability of water. If strong oxidants like oxygen, chlorine, etc., are present, the redox potential is high and positive. Groundwater containing no oxygen would have a negative value. There may be waters with a high concentration of the disinfectant. However, this quantity might not be available for the disinfection process, because of the presence of chlorine using impurities. All the chlorine would be used for oxidation rather than disinfection. Due to the fact that the redox potential measures the relation of both oxidizing and reducing compounds it gives a reliable statement about the still available disinfection power within the water. Especially at low levels, the redox potential is more sensitive than the chlorine analysis. During the conservational chlorination mode, it was sometimes not even possible to detect chlorine by analysis. However, studies of the continuously measured redox potential gave information on the microbiological quality at any time and helped the setting of the chlorine dose. Later, when no chlorination was performed at all, the level of the redox potential remained greater than 600 mv. This assured the good microbiological quality of the water. It was empirically derived that at a redox potential value of 600 mv bacteria cannot survive 8. The following methods are generally used for determination of chlorine and chloroamines: 1. DPD Colorimetric Method When N, N-diethyl-p-phenylenediamine (DPD) reacts with chlorine at a ph close to 7, the Wurster dye is the main oxidation product. Its color has been measured photometrically at wavelengths ranging from 490 to 555 nanometers (nm). At higher oxidant levels, the formation of the unstable colorless imine happens resulting in apparent fading of the colored solution. 2. Titrimetry Methods Titrimetry is performed either by macro- or by microscale methods. The micro-scale methods have the following advantages: convenience, rapidity, increased safety, reduced chemical and equipment costs, the ability to decrease the problems of chemical use and reduced waste generation. Further, microscale titrimetric analysis enhances improve learners scientific skills (A) DPD Titration Method In this method, the DPD is oxidized by chlorine to the magenta-color species which are then titrated with a ferrous reducing agent to the colorless end point. (B) Amperometric Titration Method In the amperometric determination of free chlorine, chlorine is titrated with a standard reducing agent, phenyl arsine oxide (PAO) at ph 7. A small potential is applied across the electrodes before the titration begins. During the course of titration, chlorine undergoes reaction with PAO and is reduced at the cathode to chloride. PAO is oxidized from +3 to +5 oxidation state at the anode. As long as the oxidant (free chlorine) is present in the titrated sample, a current flows through the cell. At the end point of titration, the rate of current change is zero because all of the oxidant has reacted. After the end point is reached, the solution cannot conduct current even if excess PAO is added. The amount of PAO used at the titration end point is proportional to the chlorine concentration in the sample. (C) Iodometric Titration This method is generally used for total chlorine testing at levels above 1ppm chlorine. The titration usually is performed at sample temperature below 20 C and ph range of 3 to 4. The determination is based on the oxidation of potassium iodide by the free chlorine present in water. The liberated iodine is estimated by titrating against standard sodium thiosulphate (hypo) solution, 13

4 using starch as an indicator. The end point of the titration is indicated by the disappearance of the blue color. Table 2 lists and compares the common methods used for analysis of free or total chlorine disinfectants in water 6. Method Table 2: Comparison of Common Methods for Analysis of Free or Total Chlorine Disinfectants in Water Analysis Range (ppm) Detection limit (ppm) Estimated Precision (%RSD) Application Skill Level needed DPD Colorimetric % Free and Total Low DPD Titration % Free and Total Moderate Amperometric Up to % Free and Total High Titration (Forward) Amperometric % Total High Titration (Back) Iodometric Up to 4% 1 Not reported Total Oxidants Moderate The current state of literature demonstrates that the study of residual free chlorine determination using drop number titration method and exploration of statistical, pragmatic, psychological and philosophical reasons 13 is potentially able to make a substantive contribution to the literature. The Scope and Objectives: i) How can students find residual free chlorine in water samples by employing fewer quantities of easily available reagents? ii) Will the proposed method be accurate, fast, costeffective, authentic and safe? iii) Is the proposed method capable to actively engage students in relevant, meaningful and productive ways? 2. Experimental Apparatus Specially designed measuring cylinder and conical flask were used during the experiment. (a) The extra wide mouth of measuring cylinder helps in easier and accurate collection of the number of drops for a given volume for calibration of Pasteur pipettes. (b) The funnel integral at the mouth of the conical flask facilitate titrations by drop number method. Reagents All chemicals used were of laboratory reagent grade. The sodium thiosulphate (assay 98%) and potassium iodide supplied by Qualikems Fine Chemicals Pvt. Ltd, India was used. Distilled water was used throughout the experimental studies. Solutions Standard Sodium thiosulphate (Hypo) Solution, N A N hypo solution was prepared by dissolving g of hydrated sodium thiosulphate in distilled water and diluting to 1 L. Starch Indicator Solution A starch indicator solution was prepared fresh by dissolving 1g of sodium starch glycollate in water to obtain a paste. This paste was gradually added to 100 ml of boiling water with constant stirring, boiled for a minute and then cooled before use. Experimental Procedure An environmental benign method using plastic Pasteur pipettes is described in this section. I) Calibration of Pasteur pipette A Pasteur pipette was used for delivering drops of sample water. Number of drops in 1 ml formed by sample water was collected in a measuring cylinder with integral funnel. The reverse of number of drops formed by 1 ml of sample water gives average volume of 1 drop of sample water solution. Similarly, average volume of 1 drop of hypo solution was determined. II) Titration by Drop Counting 5 ml of given water sample was accurately measured using a pipette and transferred into a titration flask. Few drops of glacial acetic acid were added to it for maintaining ph in the range of 3-4. The initial brown color of the solution was observed on addition of 1g KI. 10 drops of this brown solution were placed in clean 10 ml conical flask with integral funnel. This was titrated against 0.001N hypo solution till a light yellow color persisted. 1-2 drops of freshly prepared starch solution were added to it. The solution turned blue or violet in color. The hypo solution was added continuously till blue or violet color disappeared at the end point. The number of drops of hypo solution till the end point was noted down. The procedure 14

5 was repeated 4-5 times. The concordant or average number of drops of hypo consumed was multiplied by the average volume per drop to calculate volume of hypo, V 2. The average volume per drop of sample water was multiplied by 10 to calculate volume of sample water, V 1. The amount of free chlorine in the measured aliquot was calculated by using the following equation: Free chlorine (ppm) = N 2 V /V 1 (2) Where, N 2 = Normal concentration of hypo solution; V 2 = Volume of hypo consumed during titration, ml; V 1 = Volume of sample water taken for analysis, ml. Statistical Sampling Five students were included in one batch, each student were directed to take 5 observations. Five such batches were made. Total 125 samples were tested by drop number method. From the reported results of amount of free chlorine for tested samples, values of Average, standard deviation, relative standard deviation, Coefficient of variation and the confidence interval of mean at 95% were calculated. The closeness of a measured value to the reference (actual or true) value is known as Accuracy. Each element s average difference from the mean of the data set represents Standard deviation. Standard deviation divided by mean is Relative Standard Deviation (RSD) or The Coefficient of variation or Coefficient of dispersion. RSD is also a measure of precision (the closeness of measured values to each other) of the method Results and Discussion Titration by drop counting was done in this study. As per the normality equation: (N 1 V 1 ) of water sample = (N 2 V 2 ) of Hypo; Less volume of water sample (V 1 ) was taken to get the end point at less volume of hypo solution (V 2 ) when N 1 and N 2 are assumed to be equal. For titration, working with less volume is desirable because it helps in saving distilled water (costly resource). The concentration of chlorine in water is less (so N 1 is less), Hypo of less N 2 (say 0.001N made by dissolving g Hypo in 1 liter of distilled water, instead of 0.1N made by dissolving g/l) was used for training of students. Low normality (0.001N) of hypo solution helps in estimation of residual free chlorine in water by employing fewer quantities of hypo. Statistical comparison of performance of students The mean value of the results of 25 samples reported by a batch of five students, were used to calculate statistical parameters. The statistical results of 5 such batches are comparatively shown in Fig. 1. Fig. 1 Statistical Comparison of Results of Residual Free Chlorine Determination by Five Batches, each batch had 5 students, each student had taken 4-6 observations. 15

6 Result of 5 th batch students has a small standard deviation (relative to the mean score). This indicates that the majority of individuals (or data points) tend to have scores that are very close to the mean. By contrast the results of other batches have a large standard deviation (relative to the mean score). This indicates that the majority of individuals (or data points) tend to have scores that are more widely spread-out from the mean, perhaps with only a few cases actually having scores that fall close to the mean. 5 th batch students obtained precise results compared to other students. A small value of the coefficient of variation for 5 th batch students compared to other students suggests that the result has the smaller relative variation, or dispersion. It indicates that the proposed method is authentic and accurate. Pragmatic, psychological and philosophical reasons for the drop number titrimetry method of residual free chlorine determination in water were also explored (Fig.2), and the results are summarized in Table 3. Fig.2: Exploration of Statistical, Pragmatic, Psychological and Philosophical reasons Table 3: Exploration of pragmatic, psychological and philosophical reasons for the determination of residual free chlorine in water by drop number titrimetry method Conventional Method Drop Number Method Resource and management implications (Pragmatic reasons) Demand on resources Moderate Small Organization of required Relatively difficult Easy materials beforehand Time requirements More Less Risk Factor Moderate Small Possibility to interrupt for explaining some procedural or conceptual aspect Possible Easily possible 16

7 Authenticity as Possibility of manipulation of Less More scientific process equipment by students (philosophical reasons) Authenticity Limited Limited Learning and Development of procedural and Promotes Promotes engagement manipulative skills (Psychological reasons) Engagement in understanding the Active More active purpose of the process. Positive Outcome of this study: The above study revealed that titration by drop number method was similar to conventional titrimetry in terms of technical skills such as observations, data collection, processing of data, analysis of the result, problem solving, teamwork, communication skills etc. However, conventional titrimetry is expensive in terms of consumables and the time of academic and technical staff. As drop number method saves huge time and resources, so detailed discussion on experimental design, investigation, critical analysis of results, and sources of error can be done in the lab period itself. This method helps in reducing reagent consumption and minimizing of waste generation, thus it meets the requisites necessary to attain the Green Analytical Chemistry (GAC) recommendation 15. This work has extended the scope of environmentally benign method used for the training of first year UG students 16. Limitations: During exploration of this novel procedure, students measured volume by drops, which is not a strict unit of measurement. Size, shape and number of drops get modified by the material of the pipettes, temperature, and the other characters of the solutions. Although the identified variables were kept constant, but still there was variation in the results. Our students had varied experiences in high school chemistry as they studied in different schools under the guidance of different teachers. Their cultural and economic backgrounds were also different. We therefore do not know what effect this may have had on our findings. Directions for further research: New ways of creating smaller, reproducible drops could be innovated and tested so that requirements of time, cost and quantity of chemicals are reduced. Innovative methods needed to be explored to minimize variation in results due to different academic, cultural and economic backgrounds of the students. 4. Conclusion We have developed and validated environmentally friendly analytical procedure for training of students for estimation of residual free chlorine in water. The drop number method was found to be fast, safe and cost-effective. The study revealed that students can be effectively trained in less time using easily affordable laboratory equipment and easily available reagents in low quantities. Green approach is simple, reliable, accurate, precise, reproducible, and eco-friendly. Acknowledgements Shashi Chawla is greatly indebted to Dr Ashok K Chauhan, Founder President, Amity Universities. He is also thankful to Prof. B. P. Singh, Senior Director and Prof. Rekha Agarwal, Director of Amity School of Engineering & Technology for their continued guidance and encouragement. Special thanks are due to Ms Vyoma and Mr Ritvik for their helpful suggestions for improvements in the language. References 1. Sharma J.K., Operations Research - Theory and Applications, 3 rd edition, (Macmillan India Limited, New Delhi, pp , (2009). 17

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