International Journal of Chemical and Pharmaceutical ... Delhi final.pdfInternational Journal of Chemical and Pharmaceutical Review and Research ... was reported for determination

Int. J. Chem. Pharm. Rev. Res. Vol (1), Issue (2), 2015, Page. 49-54 ISSN No: 2395-3306 Research Article

International Journal of Chemical and Pharmaceutical Review and Research

www.ijcprr.com/browse-journal

Environmentally Benign Method for Estimation of Hardness in Water S. Chawla1, and R.K. Parashar2*

1. Department of Applied Chemistry and Environmental Sciences, Amity School of Engineering & Technology, New Delhi, India 2. 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 17 April 2015 Accepted 22 June 2015 Available online 25 June 2015 Keywords: Microscale titrimetric analysis, Titration by drop counting, Hardness of water.

A B S T R A C T Water hardness is defined as a measure of the amount of polyvalent metallic cations dissolved in water. Water with hardness above 200 mg/L causes scale deposition in pipes of the distribution systems. Soft water, with hardness less than 100 mg/L, has a bigger tendency to cause corrosion of pipes. For the estimation of hardness in water, main limitations in the widespread use of instrumental methods are high cost of instruments and need for skilled supervision for maintenance and operations. To overcome these limitations, a novel eco-friendly micro-titration method based on counting of number of drops is reported. The novel method utilizes conical flask and measuring cylinder both with integral funnel at their mouth. The green method was used for training of first year UG students. It needed only 10% of the time, saved ≥ 90% cost of the chemicals and is safe. Statistical comparison of the results with a conventional titration method shows an excellent agreement and indicates no significant difference in precision and accuracy. The novel method is more environmentally benign. It helps in saving cost, resources, time, energy and environment.

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1. Introduction Water hardness is defined as a measure of the amount of polyvalent metallic cations dissolved in water. Hardness is caused by predominantly calcium and magnesium cations. These cations react with soap to form precipitate and with other ions present in water to form scale in boilers. Hardness is most commonly expressed as milligrams of calcium carbonate equivalent per liter1.

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* Corresponding author. E-mail address: [email protected] Present address: Department of Education in Science and Mathematics, NCERT, New Delhi, India

Water with hardness above 200 mg/L causes scale deposition in pipes of the distribution systems and also increased soap consumption. On the other hand, soft water, with hardness less than 100 mg/L, is having a greater tendency to cause corrosion of pipes, and this is resulting in the presence of certain heavy metal ions, like lead, copper, cadmium, and zinc, in drinking water2. Fish cultures and many other species rely on a steady calcium carbonate concentration. Thus, hardness in water impacts ecology3. Health problems arising from the drinking of hard water have also been reported. The World Health Organization stated that hard water may lead to cardiovascular disease4. The possible association between the risk of pancreatic cancer mortality and hardness levels in drinking water was investigated.

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The findings showed an increasing odds ratio for pancreatic cancer with decreasing levels of hardness in drinking water in Taiwan5. In the flame atomic absorption spectroscopy (AAS) technique sample is introduced to an open flame for atomization. Atom of interest absorbs light of a specific wavelength when it is passed through atom and its absorbance is measured and quantified to find concentration of individual elements in a sample. This method is simple, accurate and used for the determination of water hardness6.

AAS is laboratory based lengthy technique. It is not useful for outdoor studies and continuous in-situ measurements in an automatic manner. It has been replaced by inductively coupled plasma-optical emission spectrometry (ICP-OES) for trace metal analysis7. Ca2+ and Mg2+ selective ionophores and selective sensors were also used for hardness determination. The accuracy of these techniques was seriously affected by matrix effects, interferences and irreproducibility8. A fiber optic sensor using fluorescent transduction and a polyether antibiotic for detection of Ca2+ and Mg2+ was reported for automated, rapid water hardness analysis. This method had good detect ability and selectivity. However, the drawbacks of this method are short lifetime and long assay time9.

Hardness in tap water and upland soil extracts was determined by divalent cation selective electrode, with nearly equal selectivity to Ca2+ and Mg2+. The method was validated with standard method using chelatometric titration. However, large interferences from heavy metal and transition metal ions were observed10. Devices based on sensor array attempt to mimic some human senses such as smell and taste, in effect constituting “electronic noses” and “electronic tongues”. These devices were used for classification, characterization and quality control11-12.

Potentiometric sensor arrays which consists of a series of ion-selective electrodes (ISEs) for Ca2+, Mg2+, NH4+, K+, Na+, Li+, and H+ were also used for hardness determination in neutral waters. This method required chemometric data treatment for the multivariate sensor array13. Fluorescent molecular aptamer beacon was reported for determination of total hardness in water. This method is reagent less, reproducible, sensitive, easy to use rapid and low cost assay14. Instrumental methods involve the use of expensive instruments which are not available at most school, colleges and quality control laboratories in developing and underdeveloped nations. Even if instruments are available, their appropriate uses either require separation, extraction or masking of elements from other interfering elements. Further, several instrumental parameters must be controlled.

Conventional titrimetry is still widely used in analytical chemistry because of its simplicity with little sacrifice

in precision and accuracy. The simplicity and low cost of conventional titrimetry is more advantageous especially for macro-analysis over any instrumental methods. Complexometric titration is the standard method for the determination of total hardness as CaCO3 (mg/L). They utilize eriochrome Black T indicator. Furthermore, this method uses Ethylene diamine tetra acetic acid disodium salt (EDTA) reagent in alkaline medium maintained by ammonia-ammonium chloride buffer15-16. The micro-scale methods have following advantages: convenience, rapidity, increased safety, reduced chemical and equipment costs, ability to decrease problems of chemical use and reduced waste generation. Further, micro-scale titrimetric analysis is capable to improve learners’ scientific skills17-19. Training of students on water hardness determination has received significant attention for decades20-23. Despite much discussion, however, there is scope in existing practices for improvements in safety, eco-friendliness, time requirements and cost reductions.

2. Experimental

2.1 Apparatus

Calibrated glass wares like volumetric flasks, pipettes supplied by Borosil Glass Works Ltd India were used. The mouths of conical flask and measuring cylinder were equipped with integral funnels for ease and accurate performance.

2.2 Reagents

All chemicals used were of laboratory reagent grade. Distilled water was used for making the solutions. The disodium salt of EDTA (assay 98%), and Eriochrome Black T indicator supplied by Qualikems Laboratory Reagent, Qualikems Fine Chemicals, Pvt. Ltd, India were used. Ammonium hydroxide-ammonium chloride buffer solution supplied by Merck Specialties Private Limited, India was used.

2.3 Solutions

Standard EDTA Solution, 0.01 M: An approximately 0.01 M solution was prepared by dissolving 3.7224 g EDTA in distilled water and diluted to 1L. The solution was standardized with standard calcium carbonate solution complexometrically, kept in transparent bottle, and stored at room temperature24. Eriochrome black-T (EBT). Indicator solution was prepared by dissolving 0.12 g of EBT in ethanol.

2.4 Procedure

2.4.1 Conventional Titrimetry (Method A: Macroscale)

10 ml of the hard water sample was placed in clean 100 ml conical flask. To this were added 1 ml of ammonium

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chloride in concentrated ammonia buffer and 2-3 drops of Eriochrome Black T Indicator. This was titrated against 0.01 M EDTA solution until there was color change from wine red to blue. The titre value was noted down. The procedure was repeated 4-5 times and calculations were done with either concordant or the average value. The amount of hardness in the measured aliquot was calculated by using the following equation:

Hardness (g/L) = M2V2Mw/nV1 (1)

where M2 = Molar concentration of EDTA, V2 = Volume of EDTA consumed, mL, Mw = relative molecular mass of MgSO4.7H2O (246.47), n is the reaction stoichiometry (number of moles of EDTA reactive with each mole of MgSO4.7H2O), n = 1, and V1 is the volume of hard water taken, mL22.

2.4.2 Green Approaches (Methods B1 and B2: Microscale)

Green approach using pasture pipettes is described in this section.

I) Calibration of pasture pipette

Measuring cylinder with integral funnel, shown in Fig.1, was used to collect number of drops formed by hard water and EDTA. Reverse of number of drops in 1 mL formed by hard water and EDTA using separate pasture pipettes given average volume of 1 drop of these solutions, respectively.

Fig. 1 (a) The extra wide mouth of measuring cylinder. (b) The funnel integral at the mouth of conical flask facilitate titrations by drop number method.

II) Titration by Drop Counting

“Green approach “B1”: 10 drops of the hard water sample were placed in clean 10 mL conical flask with integral funnel, shown in Fig.1. To this were added 2 drops of ammonium chloride in concentrated ammonia buffer and 1 drop of Eriochrome Black T Indicator. This was titrated against 0.01 M EDTA solution. Hardness in water was determined by counting number of drops of EDTA added till color changes from wine red to blue. The observation was recorded. The procedure was repeated 4-5 times. The concordant or average number of drops of EDTA consumed was multiplied with the average volume per drop to calculate volume of EDTA. The average volume per drop of hard water was multiplied with 10 to calculate volume of hard water. The amount of hardness in the measured aliquot was calculated by using the equation (1) as described earlier.

“Green approach “B2”: The first observation was taken as per the method described above in Green approach “B1”. For the second and subsequent observations, the titrations were continued in the same conical flask one after the other without discarding anything. Only 10 drops of hard water were added in a conical flask, the buffer and indicator were not added again as they were already present. The amount of hardness in the measured aliquot was calculated by using the equation (1) as described earlier.

2.5 Statistical Sampling Each student was directed to take 4-6 observations. 5 students were included in one batch. Five such batches (each having 5 students) were made and they repeated experiment on different timings. More than 125 samples were tested by drop number method. From the reported results of hardness for 125 samples, values of five standard statistical parameters, viz. average, standard deviation, relative standard deviation, coefficient of variation and confidence interval of the mean at 95% were calculated. Accuracy is how close a measured value is to the reference (actual or true) value. Standard deviation represents each element’s “average difference” from the mean of the data set. Relative Standard Deviation (RSD) or The Coefficient of variation or Coefficient of dispersion is standard deviation divided by mean. It is generally expressed as a percentage. RSD is useful in comparing distributions where the units may be different because it is independent of the units used. It is also a measure of precision of the method. Precision is how close the measured values are to each other. Student’s t-test and the variance ratio test (F-test) were used to determine whether the analytical procedure had been accurate and/or precise, or if it was superior to another method 25.

(a)

(b)

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3. Results and Discussion

3.1 Accuracy and Precision

The results of this study are compiled in Table 1 and shown in Fig.2. The accuracy of an analytical method expresses the closeness between the reference value and the found value. It was determined as the percentage relative error between the measured and taken amounts/concentrations. The repeatability of the proposed method was determined by performing replicate determinations (n = 5).

Fig. 2 Standard value, mean hardness and standard deviation values for conventional titrimetric (1) and green approaches (2-3).

The results of Green approach “B1” speak of good intermediate accuracy (Percent Relative Error, %RE ≤ 0.4) and precision (Percent Relative Standard Deviation, %RSD ≤ 0.9).

Table 1: Accuracy and precision comparisons of results obtained for Conventional & Environmentally benign methods of Water Hardness Determination.

Method MgSO4 taken (g/L)

Accuracy and Precision C. I of the mean at 95%. *MgSO4

found

(Mean±SD)

RE%

RSD% or (CV)

(1) Conventional

2.46 2.43±0.045

1.27

1.84 2.43±0.056

(2) “Green “B1”

2.46 2.47±0.022

0.41

0.91 2.47±0.0278

(3) “Green “B2”

2.46 2.36±0.0137

4.07

5.80 2.36±0.170

*Mean value of results of 75 samples reported by five groups of students, each group had taken 4-6 observations.

The results obtained were compared statistically by the Student’s t-test and the variance-ratio F-test and are summarized in Table 2. The calculated F-values did not exceed the tabulated value of 6.39 at the 95% confidence level. Thus the methods have comparable precisions (standard deviations) and so the t-test can be used with confidence. The calculated t- values did not exceed the tabulated value 2.306 (t) at the 95% confidence level and for (n1+n2-2) i.e. eight degrees of freedom. Thus, there is no significant difference, at the specified probability, between the mean results of the two methods. The analytical results in Tables 1-2 suggest that there is good agreement between the proposed and existing methods22.

Table 2. Results of the conventional titrimetric and proposed green approach for hardness estimation.

Method Hardness present (g/L)

Hardness found*

t F

Conventional 2.46 2.43±0.04 0.09 0.207

“Green “B1” 2.46 2.47±0.02 0.09 0.00397

*Mean value of results of 75 samples reported by five groups of students, each group had taken 4-6 observations.

The validity of the green approach needed comparison of the obtained results with those of conventional results.

3.2 Procedure validity and comparative studies

The green approach proved to be reproducible and precise. This is apparent from Tables 1 and 2. More precise and accurate results are obtained from this method since no stringent conditions to be maintained. The proposed method utilizes easily available reagents in 10-20 times smaller quantities which demonstrates cost-effectiveness. The green approach discussed in this manuscript belongs to environmentally benign procedures26-27. The findings suggest that procedure of green approach should be applicable for all types of volumetric titrations and can be used for training of the students in laboratories of schools and colleges. As lot of time is saved during actual performance so either more experiments can be included in the curricular design or more time can be allotted to teachers for explaining the theory behind the experiment.

Limitations: Each drop needs to be carefully added and counted otherwise results obtained will have errors.

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4. Conclusion This article concerns with the investigation of a green approach for determination of hardness of water. The green approach needed only 10% of the time, saved ≥ 90% cost of the chemicals and is safe. Statistical comparison of the results with a conventional titration method provided evidence for the excellent agreement between the two methods. The study revealed that persons can be trained easily using easily affordable laboratory equipment and easily available reagents in low quantities. Furthermore it was observed that green approach is simple, reliable, accurate, precise, reproducible, eco-friendly and cost-effective. Acknowledgement Authors are greatly indebted to Dr. Ashok K Chauhan, Founder President, Amity Universities thankful to Prof. B.P.Singh, Senior Director and Dr. Rekha Agarwal, Director, Amity School of Engineering & Technology, New Delhi, India and his mother Mrs Santosh Chawla for their continued guidance and encouragement. References 1. Lehr, J.H.; Gass, T.E.; Pettyjohn, W.A.; DeMarre, J. Domestic Water Treatment, McGraw-Hill Book Company, New York., (1980). 2. Naeem Khan, et al. Physiochemical evaluation of the drinking water sources from district Kohat, Khyber Pakhtunkhwa, Pakistan. Int. J Water Resour. Environ. Eng 4(10): 302-313, (2012). doi: 10.5897/IJWREE12.105 3. Wurts, W.A. World Aquaculture., 24:18, (2006). 4. Chambon, P., et al Guidelines for Drinking-water Quality.WHO/EOS/98.1,(1998). http://www.who.int/water_sanitation_health/dwq/2edaddvol2a.pdf (accessed Dec 2012). 5. Yang, C.Y. Pancreatic cancer mortality and total hardness levels in taiwan's drinking water. J Toxicol Environ Health,. 56(5): 361-369, (1999). 6. Campbell, J.; Peterson, D. Determination of water hardness from common water sources using flame atomic absorbance spectrometry. Concordia Coll. J. Anal. Chem. 1: 4-8, (2010). 7. Singh, K.P.; Malik, A.; Sinha, S. Water quality assessment and aortionment of pollution sources of Gomti river (India) using multivariate statistical techniques- a case study. Analytica Chimica Acta. 538, 355-374, (2005).

8. Rondinini, S.; Mussini, P.R.; Vertova, A.; Bortoluzzi, A.; Bono, L. ; Longhi, P. A new, long-lived Ca-selective electrode. Sens. Actuators B: Chem. B 23(1):27, (1995). 9. Suzuki, K.; Tohda, K.; Tanda, Y.; Ohzora, H.; Nishihama, S.; Inoue, H.; Shirai, T. Fiber-Optic Magnesium and Calcium Ion Sensor Based on a Natural Carboxylic Polyether Antibiotic. Anal. Chem. 61: 382-384, (1989). 10. Numata, M.; Baba, K.; Hemmi, A.; Hachiya, H.; Ito, S.; Masadome, T.; Asano, Y.; Ohkubo, S.; Gomi, T.; Imato, T.; Hobo, Y.; Determination of hardness in tap water and upland soil extracts using a long-term stable divalent cation selective electrode based on a lipophilic acrylate resin as a membrane matrix. Talanta. 55(3): 449-57, (2001). 11. Zubritsky, E. Spotting a microarray system. Anal Chem, 72(23): 761A–767A, (2000). 12. Krantz-Rulcker, C.; Stenberg, M.; Winquist, F.; Lundstrom, I. Electronic tongues for environmental monitoring based on sensor arrays and pattern recognition: a review. Anal.Chim. Acta. 426: 21-226, (2001). 13. Saurina, J.; Lopez-Aviles, E.; Moal, A.L.; Hernandez-Cassou, S. Determination of calcium and total hardness in natural waters using a potentiometric sensor array. Analytica Chimica Acta., 464: 89-98, (2002). 14. Lerga, T.M.; Sullivan, C.K. Rapid determination of total hardness in water using fluorescent molecular aptamer beacon. Analytica Chimica Acta. 610:105-111, (2008). 15. Burgot, J.L. Complexometry III: Metal Cation Indicators and Types of EDTA Titrations, Ionic Equilibria. Analytical Chemistry, Springer New York, 525-541, (2012). 16. APHA, AWWA, WEF Standard method (2340 C-2011) for the examination of water and waste water, 22nd edn. USA, (2012). 17. Singh, M.M.; Ibanez, J.G.; Esparza, M.H.; Serrano, C.D.; Infante, A.F. Environmental Chemistry, Microscale Laboratory Experiments, Springer Science + Business Media, LLC, New York, (2008). 18. Salinee, A.; Suwannathada, J. The development of microscale laboratory: titration. Int. J. Arts and Sci., 3(9): 296-305, (2010). 19. Kelkar, S.L.; Dhavale, D.D.; Pol, P.G. Microscale experiments in chemistry — the need of the new millennium. Resonance, 6 (2):14-22, (2001).

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International Journal of Chemical and Pharmaceutical ... Delhi final.pdfInternational Journal of Chemical and Pharmaceutical Review and Research ... was reported for determination