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hardness.docx | Ethylenediaminetetraacetic Acid | Magnesium
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PREAMBLE (NOT PART OF THE STANDARD) In order to promote public education and public safety, equal justice for
all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them. END OF PREAMBLE (NOT PART OF THE STANDARD) IS 3025 (Part 21) : 2009
Indian Standard METHODS OF SAMPLING AND TEST (PHYSICAL AND CHEMICAL) FOR WATER AND WASTEWATER PART 21 HARDNESS
(Second Revision) ICS 13.060.50 © BIS 2009 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 December 2009 Price Group 3
This Indian Standard (Part 21) (Second Revision) was adopted by the Bureau of Indian Standards, after the draft finalized by the Environment Protection and Waste Management Sectional Committee had been approved by the Chemical Division Council. In most natural waters, hardness is mainly due to calcium and magnesium ions. In some waters, measurable concentrations of iron, aluminium, manganese, barium, zinc and other metals may be present. Total hardness of water is the sum of the concentrations of all the metallic cations other than cations of alkali metals, expressed as equivalent calcium carbonate concentration. When the hardness is numerically greater than the sum of carbonate alkalinity and bicarbonate alkalinity; the amount of hardness which is equivalent
2 The EDTA method is based on the reaction of calcium and magnesium salts with ethylenediamine tetraacetic acid or its disodium salt and is applicable to all types of water but not applicable to wastewater. In reporting the result of a test or analysis made in accordance with this standard. silicates. phosphates. observed or calculated. it shall be done in accordance with IS 2: 1960 ‘Rules for rounding off numerical values (revised)’. the title of this standard is changed to ‘Hardness’. 1. and (b) Method based on analytical data and also the methods for determination of carbonate and non-carbonate hardness. 2 REFERENCES . Accordingly. is to be rounded off. Some waters containing high concentrations of borates. namely (a) Ethylenediamine tetraacetic acetate acid (EDTA) method.to total alkalinity is called ‘carbonate hardness’ and the amount of hardness in excess of this is called ‘non-carbonate hardness’. There is no ISO Standard on the subject. the method based on analytical data shall be used. In case of dispute.1 This standard prescribes two methods for determination of total hardness. The composition of the Committee responsible for the formulation of this standard is given in Annex A. may contribute to total alkalinity. The analytical data method is based on computation from analytical results of the sample and is applicable to water and waste water. ii Indian Standard METHODS OF SAMPLING AND TEST (PHYSICAL AND CHEMICAL) FOR WATER AND WASTEWATER PART 21 HARDNESS (Second Revision) 1 SCOPE 1. In this revision methods for determination of carbonate and non-carbonate hardness have been incorporated based on the relevance of these requirements in this field. if the final value. The first revision of this standard was published in 1983 by superseding 16 of IS 3025: 1964 ‘Methods of sampling and test (physical and chemical) for water used in industry’.
5 EDTA METHOD FOR DETERMINATION OF TOTAL HARDNESS 5. All standards are subject to revision and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below: IS No. Title 3025 Methods of sampling and test (physical and chemical) for water and waste water: (Part 1) : 1987 Sampling (first revision) (Part 23) : 1986 Alkalinity (first revision) 7022 Glossary of terms relating to water. which through reference in this text constitute provisions of this standard. At the time of publication. the editions indicated were valid. 4 SAMPLING AND PRESERVATION Sampling and sample preservation shall be done as prescribed in IS 3025 (Part 1). sewage and industrial effluents: (Part 1) : 1973 Part 1 (Part 2) : 1979 Part 2 3 TERMINOLOGY For the purpose of this standard.The Indian Standards listed below contain provisions. definitions given in IS 7022 (Part 1) and IS 7022 (Part 2) shall apply.1 Principle This method depends on ability of ethylenediamine tetraacetic acid (C10H16O8N2) .
zinc and nickel. This solution is titrated with standard solution of disodium salt of EDTA. lead. When the dye eriochrome black T (EBT) (C2OH3. N3O7S) is added to a solution containing calcium and magnesium ions at pH 10. .2.2 Interferences 5.1 The EDTA forms stable complexes with iron. copper. Heavy metal interferences can be eliminated by complexing the metals with cyanide. which extracts calcium and 1 magnesium from the dye complex and the dye is changed back to its original blue colour. zinc or lead concentrations are as high as 10 mg/1.0 a wine red complex is formed. copper. the procedure may be used even when iron. cobalt. MG++ + EBT = [Mg-EBT]′ + H+ (Pink Complex) [Mg-EBT]’ + EDTA” = [Mg-EDTA]” + [EBT]− + H+ (Blue) 5. Eriochrome black T is used to indicate the end-point for the titration of calcium and magnesium together. manganese. In the presence of cyanide.or its disodium salt to form stable complexes with calcium and magnesium ions.
NOTE—‘Pure chemicals’ shall mean chemicals that do not contain impurities which affect the result of analysis. 5.4 Phosphate and carbonate ions may precipitate calcium at the pH of titration. only pure chemicals and tannin free distilled water shall be used in tests.6H2O) in 50 ml of distilled water.25 g of magnesium salt of EDTA and dilute to 250 ml with distilled water.3. Hydroxylamine hydrochloride reagent may be used to reduce manganese to divalent state. Dilute 10 ml of the solution to 100 ml with distilled water and check that the pH value is 10.3.5. To attain the highest accuracy. 5.1.9 g ammonium chloride (NH4Cl) in 143 ml concentrated ammonium hydroxide (NH4OH). dissolve 1.7H2O) or 644 mg magnesium chloride (MgCl2.9 g ammonium chloride and 143 ml concentrated ammonium hydroxide with mixing and dilute to 250 ml with distilled water.3 Reagents 5.2. 5. Store the solution in a polyethylene bottle tightly stoppered to prevent loss of ammonia or pick-up of carbon dioxide for no longer than 1 month. The divalent manganese interference can be removed by addition of one or two small crystals of potassium ferrocyanide. add 1.3 In the absence of magnesium salt of EDTA. 5.2.3 In presence of high aluminium concentrations. the blue colour near end point starts disappearing and reverts to red. The exact amount can be determined by taking an appropriate aliquot of buffer and titrate it .2.3.179 g disodium salt of EDTA (AR quality) and 780 mg magnesium sulphate (MgSO4. adjust to exact equivalence through appropriate addition of a small amount of EDTA or magnesium sulphate or chloride. 5.0 ± 0. Add this solution to 16.1 Purity of the Reagents Unless specified otherwise.2 Buffer Solution Dissolve 16.2 The higher oxidation states of manganese above Mn++ react rapidly with the indicator to form discoloured oxidation products.
6.0 ± 0.3.4.3.6. Dilute to 1000 ml with distilled water. 5.6 Inhibitors For most waters inhibitors are not necessary.3.HCL) in demineralised water and dilute to 1 litre. addition of inhibitor sodium cyanide or sodium sulphide (NaCN or Na2S) does not sharpen the end point colour change.1.1 to 5. If interfering ions are present.5 g hydroxylamine hydrochloride (NH2OH HCL) in 100 ml 95 percent ethanol. This indicator is stable for more than 2 months.00 mg calcium carbonate (CaCO3).3.3.3 Sodium sulphide inhibitor .2 Potassium ferrocyanide crystals 5.3.6.6. inhibitors given in 5. cool. Boil for a few minutes.40 g eriochrome black T and 4.5 g EBT dye and 100 g sodium chloride in a pestle and mortar. Dry analytical grade calcium carbonate (CaCO3) in an oven at 180°C for 1 h. Alternatively. suspend it in distilled water and add 1: 1 hydrochloric acid AR quality.4 Standard Calcium Solution 1. Dilute 10 ml of the solution to 100 ml with distilled water and check that the pH value is 10. dropwise slowly to dissolve the solid. 2 5. If the end point colour change is not sharp enough it is either due to the presence of some interfering ions or due to deterioration of the indicator. In the latter case. Keep the solutions tightly stoppered to prevent loss of ammonia or absorbance of carbon dioxide and do not store for more than a month.4 may be used.00 ml = 1.3. 5. 5.5 g hydroxylamine hydrochloride in 100 ml of 95 percent ethanol or isopropanol.1 Hydroxylamine hydrochloride solution Dissolve 45 g hydroxylamine hydrochloride (NH2OH. Store in a tightly stoppered bottle. 5.5 g eriochrome black T in 100 ml triethanolamine or 2methoxyethanol or mixed 0.6. or dissolve 4.with disodium salt of EDTA as in 5. All indicator formulations tend to deteriorate especially when exposed to moisture. Use minimum amount of acid.000 g. dissolve 0.3. add a few drops of methyl red indicator and adjust to orange colour with 3 N ammonium hydroxide or 1:1 hydrochloric acid.5 Eriochrome Black T Indicator Solution Dissolve 0. Weigh 1.1.
1. Add 1 to 2 drops of indicator (5. if manganese is present. Add 1 ml buffer solution (5. As sodium cyanide is extremely poisonous. titrate slowly with continuous stirring until the reddish tinge disappears. Add 2 ml eriochrome black T indicator solution.3. At the end point the colour is sky blue. 5.4. Tightly stopper so as to avoid excessive contact with air. in a porcelain dish or 150-ml beaker and adjust the volume to approximately 50 ml. carried out in a similar way as that for sample.3.3. 5. cobalt and nickel are absent and if the sample contains less than 0. titrate with standard EDTA solution stirring rapidly in the beginning and slowly towards the end till end point is reached when all the traces of red and purple colour disappear and solution is clear sky blue in colour. in demineralized water and dilute to 1000 ml. zinc.4.2).7 g Na2S. may be used for comparison. it should be handled with care.5 g sodium cyanide (NaCN) in demineralised water and dilute to 100 ml.1 Standardization Pipette 25. Add 1 ml hydroxylamine hydrochloride (NH2OH. Add 1 to 2 ml buffer solution so as to achieve pH of 10.5H2O in 100 ml distilled water. maximum 50 ml. Surface and Saline Waters Pipette an aliquot of water sample. add 1 or 2 small crystals of potassium ferri cyanide [K4Fe(CN)6. 5. The addition of sodium cyanide or sodium sulphide may be omitted if copper. 5.4 Procedure 5. The solution should not be made acidic and should be flushed down the drain with large amounts of water when it is to be disposed off. Stir and wait for at least 5 min until sodium ferri cyanide precipitates.723 g EDTA (Na2H2C10H12ON2. Store in polyethylene bottles.2 Procedure for Drinking.Dissolve 5. Blank titration.4 Sodium cyanide solution Dissolve 2.9H2O) or 3.3.025 mg of manganese.0 ml of standard calcium solution in a porcelain basin and adjust the volume to 50 ml with distilled water. .7 Standard EDTA Solution Dissolve 3.0 g sodium sulphide (Na2S.25 mg of iron and 0.3.6. If the end point is not sharp (as determined by practice) add 2 ml sodium cyanide or sodium sulphide inhibitor solution.0 to 10. The reagent is stable for several weeks and large volume is usually prepared. adding last few drops at 3 to 5 interval.2H2O) which has been dried overnight in a sulphuric acid desiccator.5).3H2O]. Check the reagent by titrating 25 ml of standard calcium solution as described in 5. lead. solution.HCL).4.
Cool. Evaporate to near dryness and cool the beaker. For water with very low hardness (less than 5 mg/l) micro burette may be used. and X2 = Volume of ml of EDTA solution used in the titration.3 Procedure for Waste Waters and Highly Polluted Waters Digest an aliquot of the sample with 3 ml of distilled concentrated nitric acid in a beaker on a hot plate and evaporate to near dryness cautiously making sure that the sample does not boil. 2. Proceed as given in 5.5 Calculation Calculate the hardness as follows: Total hardness as = [1 000 (V1 − V2)/V3] × CF (CaCO3).2. mg/l where V1 = Volume in ml of the EDTA standard solution used in the titration for the sample.4.4. adjust to a suitable volume and take an aliquot of this digested sample. 5. V3 = Volume in ml of the sample taken for the test. Add a small quantity of 1: 1 hydrochloric acid (5 ml) and warm on a hotplate or steam-bath to dissolve the residue. Selection of sample size may be made such that the result lies between 200 to 300 mg/l of hardness (as CaCO3). Repeat digestion with nitric acid till the digestate is light in colour. X1 = Volume in ml of standard calcium solution taken for standardization.6 Report . 5. V2 = Volume in ml of the EDTA solution used in the titration for blank. CF = X1/X2 = Correction factor for standardization of EDTA.5. NOTES 1.
2 Calculation 7.2.1 Principle Total hardness computed from the concentration of the different metallic cation (other than alkali metals) in the sample but most often the cations taken into account are calcium.497 × mg/l Ca) + (4. 5.53 6.2 Calculation Total hardness (as CaCO3). NOTE—Standard deviation of 1.7 Precision and Accuracy The precision is within 1 mg/l.2 mg/l has been reported. 7.567 × mg/l Al)+ (1.3 Expression of Values of Hardness in Different Units Hardness of water shall be expressed in terms of mg/1 of calcium carbonate.1 Procedure Determine the total alkalinity as per IS 3025 (Part 23). aluminium.116 × mg/l Mg) + (2.1 Carbonate Hardness . The accuracy depends on the interfering substances present. mg/l = (2. iron. zinc.2. factors for converting the value of hardness into different-units that are in use are given in Table 1.69 × mg/l Fe) + (5. for the sake of convenience. barium and manganese. magnesium. it is within 1 mg/l. In the absence of any interference. 6. 7 CARBONATE HARDNESS AND NON-CARBONATE HARDNESS 7.Report hardness in mg/l as CaCO3 rounded to the first decimal place when the value is less than 10 mg/l and to the nearest unit if the value is more than 10 mg/l. However. 3 6 METHOD BASED ON ANALYTICAL DATA FOR DETERMINATION OF TOTAL HARDNESS 6. strontium. total hardness as in 6 and calculate the carbonate and non-carbonate hardness as given in 7.
Unit of Hardness Mg/l (as CaCO3) British Degree.058 ii) British Degree 14. Grains per US Gallon (as CaCO3) French De 00 (1) (2) (3) (4) (5) i) mg/1 as CaCO3 1.00 0. carbonate hardness (as CaCO3mg/l) is equal to total hardness (as CaCO3). b.2.00 0.16 1.07 0.83 iii) American Degree 17.00 0.70 0.04 vi) Russian Degree 2.50 0.2 Non-carbonate Hardness Non-carbonate hardness (as CaCO3).29 1.25 1. When total hardness is equal to or less than total alkalinity.15 .86 1. mg/l = total hardness .58 v) German Degree 17.a. When total hardness is greater than total alkalinity. 7.total alkalinity Table 1 Conversion Factors for Different Units for E (Clause 6. carbonate hardness (as CaCO3mg/l) is equal to total alkalinity (as CaCO3).00 iv) French Degree 10. Grains per Imperial Gallon (as CaCO3) American Degree.18 0.20 1.3) SI No.
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