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है”ह”ह

IS 15557 (2005): Methods for preparation of buffersolutions and methods for determination of pH [CHD 1:Inorganic Chemicals]

IS 15557:2005(Superseding IS 3225:1965

andlS 5741 :1970)

WRG%Tw

ZIW?fkmhTI?m+m$t-TWTpH

Indian Standard

METHODS FOR PREPARATION OF BUFFER SOLUTIONSAND METHODS FOR DETERMINATION OF pH

h

iICS 71.060.30

0 BIS 2005

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

March 2005 Price Group 7

Inorganic Chemicals and Photographic Materials Sectional Committee, CHD 1

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the drafl finalized by the InorganicChemicals and Photographic Materials Sectional Commitiee had been approved by the Chemical Division Council.

This standard has been formulated by amalgamating IS 3225:1965 ‘Methods for preparation of buffer solutions’and IS 5741 : 1970 ‘Methods for determination of pH’. IS 3225 was published in 1965 whereas IS 5741 waspublished in 1970. Since there are related standards, it was decided to amalgamate these two into one. Once, thisstandard will be published, the above two standards will be withdrawn.

In this standard, a series of buffer solution have been prescribed. It is expected that they will cover the commonexperimental conditions and be useftd for control ofpH measurement in industry. Different buffer solutions forthe same PH range have been mentioned in order to offer a choice of a particular buffer for specific experiment.

The pH is given at different temperatures for different buffer solutions as data for a uniform temperature forthese solutions were not available. It is intended to adopt a uniform temperature of 27°C for all of these solutionswhen the required data become available.

The determination of pH is the common and important control test in many chemical processing industries.Various methods of determination, ranging from simple indicator paper method to sophisticatedpH meter methods,are followed depending upon the accuracy required. The determination ofpH maybe broadly classified into twoclasses, calorimetric and electrometric methods. The calorimetric method employs indicators which develop arange of colours at different PH. The electrometric method is based on the principle that the developed emfvaries with PH.

Commercially a number of calorimetric comparators as well as the glass colour shades and indicator solutionsare available. This standard prescribes a general method for determination ofpH by calorimetry to permit the useof any commercially available comparator or device. Calorimetric determination ofpH is recommended whereapproximate pH is required. For more accurate measurement of pH, electrometric procedures are to be followed.While it is true that the pH determination by electrometric procedures maybe followed by using electrodes likehydrogen, quinhydrone, antimony and glass, this standard prescribes only glass-electrode direct-reading pHmeter as it is used largely and has many advantages over others. With the availability of special glasses, glasselectrode given very accurate results without being affected by oxidizing or reducing agents or organic substances.Moreover, glass electrode may be employed with unbuffered and small quantities of solution. It is also notpoisoned easily.

There is no ISO specification for the methods for preparation of buffer solutions and methods for determinationof pH.

The composition of the Committee responsible for formulation of this standard is given in Annex C.

In reporting the result of a test or analysis made in accordance with this standard, if the final values, observed orcalculated, is to be rounded off, it shall be done in accordance with IS 2:1960 ‘Rules for rounding off numericalvalues (revise~’.

IS 15557:2005

Indian Standard

METHODS FOR PREPARATION OF BUFFER SOLUTIONSAND METHODS FOR DETERMINATION OF pH

1 SCOPE

1.1 This standard prescribes the methods for preparationof buffer solutions used in analytical and controllaboratories in industry and the methods fordetermination ofpH by calorimetric and electrometricmethods.

1.1.1 Primary and secondary standard buffer solutionsfor calibration ofpH meters are also included in thisstandard.

1.1.2 This standard covers general methods of pHdetermination by calorimetric and glass-electrodedirect-reading pH under electrometry.

2 REFERENCES

The following standards contain provisions whichthrough reference in this text, constitute provisions ofthis standard. At the time of publication, the editionsindicated were valid. All standards are subject torevision, and parties to agreements based on thisstandard are encouraged to investigate the possibilityof applying the most recent editions of the standardsindicated below.

IS No.

695:1986

1070:19922124:2000

2711: 1979

Title

Specification for acetic acid (thirdrevision)

Reagent grade water (third revision)

Sodium bicarbonate — Specification(second revision)Direct reading pH meters (second

revision)

3 TERMINOLOGY

For the purpose of this standard, the followingdefinitions shall apply.

3.1 pH — It is a measure of the hydrogen ion activityin aqueous media. It is represented by the equation:

pH = –log10 cc~C~

where

cc~= activity coefficient of the hydrogen ion, and

CH= concentration coefilcient of the hydrogen ion.

3.2 Buffer Solution — A solution the hydrogen ionconcentration of which is not appreciably affected bythe addition of small amounts of acid or alkali.

1

3.3 Buffer Value, ~ (dm/dpH) — The moles of astrong acid or strong base when added to one Iitre of asolution to change its pH value by a unit,

3.4 Dilution Value (A pH!4) — The change of pHunits if a buffer solution is diluted with an equal volumeof water.

3.5 Indicators — Substances that behave like weakacids or weak bases, and their dissociated orundissociated forms have different constitutions andcolours.

3.6 Molality (m) (of a Solution) — The amount ofsolute in moles per 1000 g of the solvent.

3.7 Molarity (M) (of a Solution) — The amount ofsolute in moles in one litre of the solution.

3.8 Temperature Coefficient [ /]dpH

dt — The change

of pH units per degree Celsius (Centigrade) rise of

temperature.

4 REAGENTS

4.1 Unless specified otherwise, pure chemicals anddistilled water (see IS 1070) shall be employed in tests.The reagents of the purity specified against eachin 4.1.1 to 4.1.19 shall be used in the preparation ofthe buffer solutions. Freshly boiled and cooled distilledwater shall be used for the preparation of all buffersolutions.

NOTE — ‘Pure chemicals’ shall mean chemicals that do notcontain impurities which affect the results of analys is.

4.1.1 Acetic Acid — (CH~COOH; Molecular weight60.05). Pure (see IS 695).

4.1.2 Borax — (NazBdG7. 10H20; Molecular weight381.43). It shall contain not less than 99.5 percent andnot more than 100.5 percent of NazB~07. 10HZOandshall conform to the limits of impurities given below:

S1No. Impurities Percent by Weight,

Max

i) Carbonate (as COJ 0.05ii) Chloride (as Cl) 0.001

iii) Sulphate (as SOJ) 0.005iv) Calcium (as Ca) 0.01

NOTE — Before use the borax shall be gradually heated to11O“Cand then its temperature raised to 400°C to dehydrate itcompletely.

IS 15557:2005

4.1.3 Boric .4cid-(HjBO~; Molecular weight 61.84).Analytical reagent grade. Before use the material shallbe spread in a dry vacuum desiccator at roomtemperature preferably overnight.

4.1.4 CalciwnH ydroxideS o/ution—[Ca(OH)2,

Molecular weight 74.09]. Calcium hydroxide shallbe prepared from calcium carbonate of low alkaligrade after it has been washed thoroughly. Heat thecarbonate slowly to about 1 OOO°Cand ignite at thattemperature for at least 45 min. After cooling, addthe resulting calcium oxide slowly to water withstirring. Heat the suspension to boiling, cool and filteron a G3 sintered glass funnel. Dry the solid in anoven and crush to a uniform, ilnely granular state foruse.

4.1.4.1 To prepare a saturation solution, shakevigorously an excess of calcium hydroxide, preparedas in 4.1.4, in a stoppered polyethylene bottle withwater at room temperature. Allow the excess of solidto settle and remove the suspended material byfiltration with suction on a G3 sintered glass funnel. Itis advisable to determine the concentration of asaturated solution of a portion of calcium hydroxideprepared from each particular lot of calcium carbonate.If the concentration of the saturated solution at 25°Cas determined alkalimetrically appears to exceed0.0206 M, the presence of soluble alkalis is indicated.Calcium hydroxide solution shall be free from solublealkalis.

4.1.5 Disodiurn Hydrogen Phosphate — (Na2HPOJ;Molecular weight 141.97). It shall contain after dryingfor 2 hat 110~ 2“C, not less than 99.5 percent and notmore than 100.5 percent of Na2HP01. It shall conformto the limits of impurities given below:

S1No. Impurities Percent by Weight,Max

i) Chloride (as Cl) 0.006ii) Sulphate (as SOJ 0.03

iii) Potassium (as K) 0.05iv) Loss on drying at 120+ 2°C 0.2

4.1.6 Glycine — (HZN.CH2COOH; Molecular weight75.05). It shall comply with the following requirements:

a)

b)

c)

d)

e)

A solution of 2 g glycine in 20 ml of watershall be clear.

It shall give no precipitate with barium nitratesolution.

It shall show only the slightest opalescencewith silver nitrate solution.

Sulphated ash obtained from 5 g of glycineshall not exceed 2 mg.

Nitrogen content (by Kjeldahl method) shallbe 18.67+ 0.10 percent by weight.

4.1.7 Hydrochloric Acid— 0.1 N and 0.2 N.

4.1.8 Phosphoric Acid— (H~POq;Molecular weight98.0). Analytical reagent grade.

4.1.9 Potassium Hydrogen Phthafate — (HOOC.CbHd.COOK; Molecular weight 204.22). It shall contain notless than 99.9 percent and not more than 100.1 percentof HOOC.C6Hd.COOK and shall conform to the limitsof impurities given below:

S1No. Impurities Percent by Weight,

Max

i) Chloride (as Cl) 0.001ii) Sulphate (as SOt) 0.01

iii) Sodium (as Na) 0.05iv) Moisture 0.1

4.1.10 Potassium Chloride — (KCI; Molecular weight74.55). Analytical reagent grade, recrystallized severaltimes from water and dried at 120 to 150°C.

4.1.11 Potassium Dihydrogen Phosphate — (KHzPO~;Molecular weight 136.09). The material, after dryingat 110 ~ 2“C, shall contain not less than 99.5 percentand not more than 100.5 percent of KH,POd. It shallcomply with the limits of impurities as given below:

S1No. Impurities Percent by Weight,Max

i) Chloride (as Cl) 0.0005ii) Sulphate (as SOJ 0.01

iii) Ammonia (as NHJ 0.001iv) Sodium (as Na) 0.05v) Loss on drying at 110~ 2°C 0.1

4.1.12 Potassium Hydrogen Tartrate — (KHCqHIOc;Molecular weight 188. 18). The material, dried at110 ~ 2“C, shall contain not less than 99.8 percentof KHCdHd06. It shall comply with the limits ofimpurities as given below:

S1 No. Impurities Percent by Weight,Max

i) Chloride (as Cl) 0.001ii) Sulphate (as SO.) 0.01

iii) Iron (as Fe) 0.001iv) Lead (as Pb) 0.001v) Moisture 0.1

4.1.13 Potassium Tefra-oxalate — [KH3 (C20d)z.2HZO; Molecular weight 254.19]. The material shallcontain not less than 99.9 percent and not more than100.1 percent of KHJ (C20J. 2HZ0. It shall complywith the limits of impurities given below:

S1No. Impurities Percent by Weight,Max

i) Chloride (as Cl) 0.002ii) Sulphate (as SOJ 0.01

iii) Calcium (as Ca) 0.005iv) Sodium (as Na) 0.05

2

Is 15557: 200s

4.1.14 Sodium Acetate — (CH3COONa.3HzO;Molecular weight 136.08). Analytical reagent grade.

4.1.15 Sodium Bicarbonate — (NaHC03; Molecularweight 84.0 1). Analytical reagent grade (see IS 2 124).

4.1.16 Sodium Chloride — (NaCl; Molecular weight5t?.45). Analytical reagent grade.

4.1.17 Sodium Diethyl Barbiturate (Sodium SaIi ofVeronal) — (Molecular weight 206. 18). It shallcrmtain, after drying, not less than 98.5 percent ofC:H, ~OjNzNa. It shall conform to the limits ofimpurities given below:

[mpurities Percent by Weight,Max

Loss on drying at 105°C 1.0

Neutral or basic substances 0.2

Lead (as Pb) 0.001

Sodizwl Hydroxide — (NaOH; Molecular40.4 1). Carbonate — free. O.lN and 0.2N;

standardized against O.IN and 0.2N phthalic acidso~ution using phenolphthalein as indicator.

4.1.19 Tris (Hydroxymethyl) Amino Methane —[(HOCH,), = C(NH,)].

5 WORKING BUFFER SOLUTIONS FORGENERAL PURPOSES

In case of tartrates, citrates, oxalates and phthalatesworking buffer solutions either flesh solutions shall beprepared or a drop or two of thymol solution shall beadded as they are liable to get fimgus growth on storage.

5.1 Clark and Lubs Buffer Solutions (25”C)

5.?. 1 rd7 1.2 to 2.2 — Prepared by mixing hydrochloricacid (~~.2Nand potassium chloride solution) (0.2 N anddi\uting to 1 Iitre, with water).

Composition per Iitre of the solution:

Composition/Litre of the Solution pH< - >}<jdrQ~hloric Potassium Chloride

Acid Solutionm1 ml

(1) (2) (3)

425.0 + 250 1.2266.0 + 250 1.4162.0 + 25o 1.6102.(J + 25o 1.865.0 + 250 2.039.0 + 250 2.2

S.1.2 pH 2.2 to 4.0 — Prepared by mixing hydrochloricacid {0 2 N) and potassium hydrogen phthalate solution(0.2 M) and diluting to one Iitre with water.

Composition/Litreof the Solution pH/ -Hydrochloric

>Potassium Hydrogen

Acid Phthalate Solution

;; ;; (3)247.5 + 25o 2.2211.0 + 250 2.4177.0 + 250 2.644.5 + 250 2.811,5 + 250 3.078.5 + 250 3.252.0 + 250 3.431.5 + 250 3.614.5 + 250 3.820.0 + 250 4.0

5.1.3 pH 4.2 to 5.8 — Prepared by mixing sodiumhydroxide solution (0.2 N) and potassium hydrogenphthalate solution (0.2 M) and diluting to one litre withwater.

CompositiotiLitre of the Solution pH&

%odium Hydroxide Potassium Hydroge~Solution Phthalate Solution

;; ;;

15.0 + 25033.0 + 25o55.5 + 25082.5 + 250

113.0 + 250144.0 + 250170.5 + 250194.0 + 25(I211.5 + 250

(3)

4.24.44.64.85.05.25.45.65.8

5.1.4 plf 5.8 to 8.0- Prepared by mixing sodiumhydroxide solution (0:2 N) and potassium dihydrogenphosphate (0.2 M) and diluting to one litre with water.

Composition/Litre of the Solution pH

“SodiumHydrochloric P#tassium DihydrogenSolution Phosphate Solution

A;; (2)

18.0 ‘ + 25028.0 + 25040,5 + 25o58.0 +25082.0 + 250

112.0 + 250145.5 + 250173.5 + 25o195.5 + 250212.0 + 250222.5 + 250230.5 + 250

(3)

5.86,06.26.46.66.87.07.27.47.67.88.0

3

IS 15557:2005

5.1.5 pH8.Oto 10.O—Prepared by mixing sodiumhydroxide solution (0.2 N), and boric acid solution(0.2M) inpotassium chloride solution (0.2M) anddiluting to one litre with water. These solutions shall bechecked to account for the influence of carbon dioxide.

Composition/Litre of the Solution

- Sodium Hydroxide Boric Acid-Potassiu;Solution Chloride Solution

ml ml(1)

19.530.043.059.079.0104.0132.0160.5184.5203.0218.5

(2)+ 25o+ 250+ 25o+ 25o+ 250+ 250+ 250+ 250+ 250+ 250+ 250

pH

(3)8.08.28.48.6

:::9.29.4

;:;10.0

5.2 Sorensen Buffer Solution (18”C)

5.2.1 pH 1.04 to 3.68 — Prepared by mixinghydrochloric acid (O.1 N) and glycine solution (O.1 M)in sodium chloride solution (O.1 N).

Composition/Litre of the Solution pHAF

Glycine-Sodium Hydrochloride Ac~Chloride Solution ml

;; (2) (3)0.0 + 100 1.04

10.0 + 90 1.1520.0 + 80 1.2530.0 + 70 1.4240.0 + 60 1.6450.0 + 50 1.9360.0 + 40 2.2870.5 + 30 2.6180.0 + 20 2.9290.0 + 10 3.3495.0 +5 3.68

5.2.2 pH 8.24 to 10.14 — Prepared by mixing sodiumhydroxide solution (O.1 N), and glycine solution(O.1 M) in sodium chloride solution (0.1 N).

Composition/Litre of the Solution—/- Y

Glycine-Sodium Sodium HydroxideChloride Solution

;;97.595.090.080.070.060.0

Solu~ion

;;+ 2.5+ 5.0+ 10.0+ 20.0+ 30.0+ 40.0

pH

(3)8.248.588.939.369.71

10.14

5.3 Michaells Buffer Solutions (25”C)

5.3.1 Veronal — Sodium Hydroxide Buj$er Solutions

for Physiological Purposes (pH 7.00 to 9.20) –Prepared with sodium salt of veronal solution (O.1 M)and hydrochloric acid (O.1 N).

Composition/Litre of the Solution pH/ A

Sodium Salt of HydrochloricY

Veronal Solution Acid

;; ;; (3)53.6 + 46.4 7.0055.4 + 44.6 7.2058.1 +41.9 7.4061.5 + 38.5 7.6066.2 + 33.8 7.8071.6 + 28.4 8.0076.9 + 23.1 8.2082.3 + 17.7 8.4087.1 + 12.9 8.6090.8 + 9.2 8.8093.6 + 6.4 9.0095.2 + 4.8 9.20

5.3.2 Veronal—Acetate Buffer Solutions (pH2.62 to9.64) — Isotonic with blood at 250C. The veronal-acetate solution shall contain 19.43 g of sodium acetateand 29.43 g of sodium salt of veronal in 1 litre of thesolution made in carbon dioxide-free water.

5.3.2.1 To make 25 ml of buffer solution, take 5 ml ofthe veronal acetate solution (see 4.3.2) and mix 2 mlof sodium chloride solution (8.5 percent w/v) and thefollowing amounts of hydrochloric acid (O.1 N) anddilute to 25 ml with carbon dioxide-free water.

Volume of Hydrochloric Acid pHml

(1) <2)

0.0 9.640.25 9.160.50 8.900.75 8.681.0 8.552.0 8.183.0 7.904.0 7.665.0 7.425.5 7.256.0 6.996.5 6.757.0 6.128.0 5.329.0 4.93

10.0 4.6611.0 4.3312.0 4.13

IS 15557:2005

(1) (2)

13.0 3.8814.0 3.6215.0 3.2016.0 2.62

5.4 Britton and Robinson Universal Buffer Solutions(pH 1.81 to 11.98) — Prepared by adding the followingvolumes of sodium hydroxide solution (0.2 N) to100 ml of a solution of mixed acid, being 0.04 M withrespect to phosphoric acid, 0.04 N with respect to bothacetic and boric acids.

Volume ofSodium HydrochloricSolution

ml(1)

0.02.55.07.5

10.012.515.017.520.022.525.027.530.032.535.037.540.042.545.047.550.052.555.057.560.062.565.067.570.072.575.077.580.082.585.087.590.092.595.097.5

100.0

pH

(2)

1.811.891.982.092.212.362.562.873.293.784.104.354.564.785.025.335.726.096.376.596.807.007.247.547.968.368.698.959.159.379.629.91

10.3810.8811.2011.4011.5811.7011.8211.9211.98

5.5 Buffer Solution ofpH 9.6 to 13.0 (250C)

551 pH 9.6 to 11.0 — Prepared by mixing sodiumbicarbonate solution (0.05 M) and sodium hydroxidesolution (O.1 N) and diluting to one Iitre with water.

Composition/Litre of the Solution pH—

=dium Hydroxide>

BicarbonateSolution Solution

;; ;; (3)50.0 + 500 9.6076.0 + 5t)t) 9.80

107.0 + 500” 10.00138.0 + 500 10.20165.0 + 500” 10.40191.0 + 500” 10.60212.0 + 500 10.80227.0 + 500” 11,00

5.5.2 pH 10.9 to 12.0 — Prepared by mixing disodiumhydrogen phosphate solution (0.05 M) and sodiumhydroxide solution (O.1 N) and diluting to one litre withwater.

Compositior#Litre of the Solution pH/ —Sodium Hydroxide Disodium Hydrog~n

Solution Phosphate Solution

;; ;; (3)33.0 + 50(3 10.9041.0 + 5(30 11.0063.0 + 500 11.2091.0 + 500 11.40

135.0 + 5f30 11.60194.0 + 500” 11.80269.0 + 50(3 12.00

5.5.3 pH 12.0 to 13.0— Prepared by mixing potassiumchloride solution (0.2 M) and sodium hydroxidesolution (0.2 N) and diluting to one Iitre with water.

Composition/Litre of the Solution pH-

%odium Hydroxide Potassium Chlorid>Solution Solution

:; ;; (3)60.0 + 250 12.00

102.0 + 250 12.20162.0 + 25(I 12.40256.0 + 250 12.60412.0 + 250 12.80660.0 + 25o 13.00

5.6 Gomori Buffer Solutions (25”C) pH 7 to 9 forPhysiological Purposes

Prepared by mixing 0.1 M tris (hydroxymethyl)aminomethane and 0.1 N hydrochloric acid anddiluting to one litre with water.

5

1S 15557:2005

CompositionlLitre of(he Solution pH.

Hydrochloric Tris Hydroxymeth~Acid Ammomethane

Sol~~onm1(1) (2) (3)

466 + 50(3 7.00447 + 500 7.20420 + 500 7.40385 + 500 7.60345 + 500 7.80292 + 500 8.00229 + 500 8.20172 + 500 8.40124 + 500 8.6085 + 500” 8.8057 + 500 9.00

5.7 Walpole Buffer Solutions (18°C)pH 3.42 to 5.89

Prepared by mixing 0.2 N acetic acid and 0.2 M sodiumacetate solution and diluting to one litre with water.

Composition/Litre of the Solution-,-- >

Acetic Acid Sodium AcetateSolution

m 1(1) ;;

950 + 50900 + 100800 + 200700 + 3(30600 + 400500 + 500400 + 600300 + 700200 + 800150 + 850100 + 900

50 + 950

pH

(3)3.423.724.054.274.454.634.804.995.235.375.575.89

6 PRIMARY AND SECONDARY BUFFERSOLUTION

6.1 For checking the pH of solutions prepared (see 4),apH meter shall be employed which shall be calibratedagainst primary and secondary buffer solutions givenin Table 1. The solution given in a arranged in thetable in the order of increasing pH values.

7.CALORIMETRIC METHODS OFDETERMINATION OFpH

7.1 Indicator Paper Method

7.1.1 Materials

7.1.1.1 Indicator papers

Supplied in booklets carrying the colour chart of twentyleaves measuring 64 mm x 12.5 mm and of range asfollows:

Bromocresol green Methyl redphenolphthalein

Bromothymol blue Thymol blue

Chlorophenol red Thymolphthalein

Methyl orange Titan yellow(clayton yellow)

The paper may also be supplied in rolled tapes of about5 m long and 10 m wide in a convenient plasticdispenser carrying clearly the printed pH colour chart.

7.1.2 Procedure

The leaf of the indicator paper or a strip cut from thedispenser is dipped in the test solution contained in aclean test tube. Compare the colour of the moistenedindicator paper with those printed on the booklet ordispenser. The pH of the solution is designated as the

Table 1 Standard Primary and Secondary Buffer Solutions at 25°C

(Clause 6.1)

SI Buffer SoIutions Molality wei~ht(in Air)of pH at DilutionValue Buffer TemperatureN(). Buffer Substance 25°C (ApH%) Value Coeftlcient

at 25°C rlpflldt

(1) (2) (3) (4) (5) (6) (7) (8)

i) Potassium tetra-oxalate 0.05 12.61 1.679 +0.186 0.070 + 0.001ii)

iii)

iv)

v)

vi)

\ii)

Potassium hydrogen 0.034 Satordted at 25°C 3.357 + 0.049 0,027 – 0.0014tartrate (approx)

Potassium hydrogen phthalate 0.05 10.12 4.008 + 0.052 0.016 + ().()012

Potassium dihydrogen 0.025 3.39phosphate PLUS

}

6.865 + 0.080 0.029 -0.0023disodium hydrogen phosphate 0.025 3,53

Potassium dihydrogen 0.008695 1.179phosphate PLUS

}

7,413 +0.07 0.016 -0.0028disodium hydrogen phosphate 0.03043 4.30

l)orllx 0.01 3.80 9.180 +0.01 0.020 -0.0082

Calcium hydroxide 0.0203 Saturated at 25°C 12.454 -0.28 0.09 – 0,033

NIWE — Solotioo (ii) to (vi) are primary standard, and (i) and (vii) are secondary standard.

IS 15557:2005

number written on a particular colour shade with whichthe colour of the moistened indicator paper matches.[n case the colour is intermediate to two coiourstandards, express the pH to the one with which themoistened indicator paper matches more closely.

7.2 Comparator Method

7.2.0 Outline of the Method

The pH of an unknown solution is determined bytesting it with universal indicator; solution and theapproximate value is found. The pH value is thendetermined by selecting an indicator with a suitablecolour-change interval.

7.2.1 Apparatus

7.2.1.1 Comparator — Any suitable comparator withampoules of buffer solutions of known and accuratepH value to which the indicator is added. Alternatively,coloured glass slides may also be used.

NOTE — Any commercial comparator with indicator’s kit orslides is suitable.

7.2.1.2 Test tube, of glass.

7.2.2 Reagents

7.2.2.1 Indicators — The common indicators used forthe determination ofpH are listing in Annex A.

7.2.2.2 Universal indicator — Dissolve in 100 ml ofalcohol the following in the given order:

0.06 g of methyl yellow, O.0~g of methyl red, 0.08 gof bromothymol blue, 0.10 g of thymol blue, and0.02 ofphenolphthalein.

Titrate the solution to yellow colour with 0.1 N sodiumhydroxide solution. The indicator has the colour valueas given below:

a) pH 1 Cherry-red

b) pH 2 Rose

c) pH 3 Red-orange

d) pH 4 Orange-red

e) pH 5 Orange

f) pH 6 Yellow

g) PH 7 Yellow-greenh) pH 8 Green

j) pH 9 Blue-green

k) pH 10 Blue

7.2.2.3 Buffer solutions — Buffer solutions areprepared from chemicals of analytical reagent grade.They should be stored in clean bottles, each bottlecarrying the date andpH as they are liable to deterioratewith time. Commonly used buffer solutions are listedin Annex B.

The coloured buffer solutions are prepared by addingthe correct quantity of the required indicator to the

correct volume of the buffer and the solution sealed inan ampottle.

7.2.3 Procedure

To determine the pH of a solution, the indicator usedshall be one which given a colour of the solutionintermediate between those shown at the extremes ofitspH range. Determine the approximatepH by addingto a small sample of the solution a little of universalindicator and find out the range. Measure out 10 ml ofthe solution whose pH has to be measured and transferto a clean glass tube and add the correct quantity ofthe indicator. Normally 0.1 to 0.2 ml of the indicatorsolution is sufficient. The colour developed iscompared with that of the buffer tubes of known pHvalue in a comparator as given in 7.2.3.1.

7.2.3.1 Place three test tubes filled with liquids inspaces A, B and C, add the indicator to B only in thespace E provided in front of it, place a test tube filledwith distilled water. Place the buffer tubes containingthe indicator in spaces D and F and change until acorrect colour match is obtained when viewed. Thesolution is assigned the pH of the buffer with which itclosely matches (see Fig. 1).

Alternatively, the pH of a solution may be determinedusing permanent colour glass standards, usuallyarranged as circles of suitable coloured glasses fixedin a circular disc, in such a way that selection of theappropriate colour.

7.3 Electrometric Method

Electrometric pH measurements are made with asuitable electrode system which develops a potential(emt) proportional to the pH of the solution.

7.3.1 Apparatus

7.3.1.1 pH meter — Direct reading type conformingto IS2711.

7.3.1.2 Ca[omel and glass electrodes — Saturatedcalomel electrode shal! be used inpH meter assembly.A few crystals of solid potassium chloride shall bepresent within the chamber surrounding the calomelat each temperature. The design of the electrode shallbe such as to allow a fresh liquid junction between thesolution of potassium chloride and the buffer or testsolution.

The glass electrode shall be calibrated as prescribedin 7.3.2.1. If the electrodes are used outside theelectrode compartment of the assembly the leads shallbe protected from the effects of body capacitance. ,

To attain equilibrium as quickly as possible when usinga glass electrode, the electrode shall be kept underwaterwhen not in use so that it does not become dryexternally.

7

155s’ :2005

SAMPLE SAMPLE SAMPLEANDINDICATOR

i

/ -w\

(\

\ /--

/ —\ ;\

iz\

\ /--- )I

STANDARD BUFFERCONTAINING INDICATOR 1 LDISTILLED

WATER

L STANDARD BUFFERCONTAINING INDICATOR

FIG. 1 ASSEMBLY DIAGRAM OF TUBES IN A COMPARATOR

7.3.2 Procedure

7.3.2.1 Standardization

The assembly shall be put on, allowed to warm upthoroughly and brought to electrical balance as permanufacturer’s instructions. Wash the glass andcalornel electrodes and the sample cup-thoroughlytwice with distilled water and wipe dry with a cleanabsorbent paper. Note the temperature of the testsolution and adjust the temperature dial of the meterto proper setting. Select two standard solutions fromTable 1 as to bracket the anticipated pH of the testsolution and the standard solutions shall be brought tothe temperature of the test solution within 2“C. Fill thesample cup with the first standard solution and immersethe electrodes. Set the dial of the meter to the knownpH or potential corresponding to the known pH of thestandard solution at appropriate temperature. Bring themeter to the balance by engaging button and rotatingasymmetry potential knob. Fill the sample cuprepeatedly with additional portions of standard solutionuntil the meter remains in balance within + 0.02 pHunit for two successive portions without a change inthe position of the asymmetry knob. To eliminate theeffect of thermal and electrical hysteresis, thetemperature of electrodes, standard solutions and washwater shall be kept very close to that of the test solution.

Wash the electrodes and sample cup thoroughly withwater and form a fresh liquid junction. Place the second

8

standard in the cup and adjust the meter to new balancepoint and read the pH. The setting on the asymmetrypotential knob shall not be changed. Use additionalportions of second standard solution until successivereadings of pH agree within 0.05 units. The meter isdeemed to work satisfactorily if the reading obtainedfor the second standard solution is within thepermissible limits of error.

If the anticipatedpH of the solution is greater than 10,disodium tetraborate and saturated calciumhydroxide solutions (see Table 2) shall be used forstandardization. The meter, in this case, is consideredto be working satisfactorily if the reading obtained forthe second standard solution agreed with the assignedpH within 0.1 unit.

If the pH determinations are made only occasionally,the meter shall be standardized each time.

7.3.2.2 pH of test solution

Wash the electrodes and sample cup and wipe dry witha clean absorbent paper. Fill the cup with a portion ofthe test solution and form a fresh liquid junction. Themeter is operated andpH directly read. In case of wellbuffered test solution, one to three portions will usuallybe sufficient to yield pH values reducible to ~ 0.05units, In case of slightly bufferedsolutions or distilledwater six or more portions may be necessary.

7,3.2.3 Report the pH obtained for the test solution tothe nearest 0.1 unit.

IS 15557:2005

Table 2 Standard Solutions

(Ckme 7.3.2.1)

S1 Temperature pH of SolutionNo. w

0.05 M 0.05 M 0.025 M Potassium 0.01 M Saturated CalciumPotassium Potassium Dihydrogen Phosphate+ 0,025 M Dkodium }IydroxideTetroxalate Hydrogen Disodium Hydrogen Tetraborate

Phthalate Phosphate

(1) (2) (3) (4) (5) (6) (7)

i) o 1.67 4.01 6.98 9.46 13.43

ii) 10 1.67 4.00 6.92 9.33 13.00

iii) 20 I .68 4.00 6.88 9.22 12.63

iv) 25 1.68 4.01 6.86 9.18 12.45

v) 30 1.69 4.01 6.85 9.14 12.30

vi) 35 1.69 4.02 6.84 9.10 12.14

vii) 40 1.70 4.03 6.84 9.07 11.99

viii) 50 1.71 4.06 6.83 9.01 11.58

ix) 60 1.73 4.09 6.84 8.96 11.45

9

IS 15557:2005

ANNEX A

(C/ause 7.2.2.1)

INDICATORS FOR DETERMINATION OFpH

,4-1 PREPARATION the quantity of the indicator material with the volume

The indicators shall be prepared as shown in Table 3. of 0.02 N sodium hydroxide solution, in an agate

The water used for preparation shall be carbon dicrxide-mortar, and dilute with carbon dioxide-free water to

free Similarly ethyl alcohol used should also be the volume indicated.

neutral. When the indicator solution is to be prepared NOTE — The commercially avrrilabk, ready to use indicator

with CI.02N sodium hydroxide solution, tritrate well solutionsmay also be used for determination ofpH,

Table 3 Preparation of Indicator Solution

(Clause A-1. 1)

SI Indicator Range Colour PreparationNo. ~

(1) (2) (3) (4) (5) (6)

i)

ii)

iii)

iv)

~)

vi)

vii)

viii)

lx)

x)

\i)

xii)

xiii)

Xtvj

xl’)

“rhymol blue

McthyL)’Ci[OW

Methyl orange

Bromophenol blue

Bromocresol green

Methyl red

13romothvmolblue

Phenol red

Metacresrd purple

Thymol blue

Pknoiphthalein

Thymolphthalein

Alirdrine yellow

Nitrdminc

1.3. 5-Trinitrobenzerre

1.2 to 2.8

2.9104.0

3.1 to 4.4

3.0 to 4.6

3.8 to 5.4

4.2 to 6.3

6.0 to 7.6

64 to 8.0

7.4 to 9.0

80t09,6

8.2 to 9.8

9.3 to 10.5

lo.lto12.o

11.oto 13.0

11.5 to 14.0

Red

Rtx!

Red

Yellow

Red

Yellow

Ye!inw

Yellow

Cokmr-iess

Colour-kss

Yellow

Yellow

Colour-less

Yellow

YeBow

Orange-Yellow

Blue-Violet

Blue

Yellow

Blue

Red

Purple ‘“

Blue

Red-Violet

Bhre

Vwlet

Orange-Brown

Yellow

Dissove 0.10 g in 10.75 ml of 0.02 N sodiumhydroxide an~dihrte to 250 ml with water

Dissolve 0.10 g in 100 ml of alcohol

Dissolve 0.2 g in 100 ml of hot water

Dksolve 0.10 g in 7.45 ml of 0.02 Nhydroxide and dilute to 250 ml with water

Dksolve 0.10 g in 7.15 ml of 0.02 Nhydroxide and dilute to 250 ml with water

Dissolve 0.10 g in 18.6 ml of 0.02 Nhydroxide and dilute to 250 ml with water

Dissolve 0.10 g in 8.0 ml of 0.02 Nhydroxide and dilute to 250 ml with water

Dissolve O.10 g in 14.20 ml of 0.02 Nhydroxide and dilute to 250 ml with water

Dissolve 0,10 g in 13.I ml of 0.02 Nhydroxide and dilute to 250 ml w,ithwater

sodium

sodium

sodium

sodium

sodium

sodium

Dissolve 0. IOg in 10.75 ml of O,(I2Nsodiumhydroxide and dilute to 250 ml with water

Dissolve 0.10 g in 100 ml of 80 percent alcohol

Dksove 0.10 g in 100 ml of 80 percent alcohol

Dksolve 0.10 g in 100 ml of 50 percent alcohol

Dksolve 0.10 @tr 100 ml of 70 percent alcohol

Dksolve 0.10 g in 100 ml of alcohol

10

IS 15557:2005

ANNEX B

(Clause 7.2.2.3)

BUFFER SOLUTION

B-1 Buffer solutions shall be prepared by diluting the specified quantity of solution given below to 100 ml:

pH Solutionat

20°c MIS M15 MI1O MI1O M/l OSodium M/l OPotassium M/l OBoricPotassium Hydrochloric Potassium Hydrochloric Hydroxide Dihydrogen Acid and MI1OChloride Acid Hydrogen Acid Orthophosphate Potassium

Phthalate Chlorideml ml ml ml ml ml ml

(1) (2) (3) (4) (5) (6) (7) (8)

1.01.21.41.61.8

2.02.22.42.62.8

3.03.23.43.63.8

4.04.24.44.64.8

5.05.25.45.65.8

6.0

6.26.46.66.8

7.07,2

7.47.67.8

2525252525

2525—

.—

—

—

———

—

—

—

———

,——

48.532.2520.7513.158.3

5.33.35

———

—————

—————

————

—

————

—————

—————

(5;)505050

5050505050

5050505050

5050505050

50

————

———

—————

(46~70)39.6032.9526.42

20.3214.709.905.972.63

—————

—————

————

—————

—

——

—————

—————

0.403.707.5012.1517.70

23.8529.9535.4539.8543.00

45.45(5.70)8.6012.6017.8023,65

29.6335.0039.5042.8045.20(2.61)

—

———

———

—

——

————

———

(50)50505050

5050505050

—————

—————

—————

—————

—————

—

————

———

(5;)

.

11

IS 15557:2005

(1) (2) (3) (4) (5) (6) (7) (8)

8.0 – – — 46.80 50 (50)(3.97)

s,~ – — — 5.90 — 508.4 – — — — 8.50 — 508.6 – — — 12.00 — 508.8 — — — — 16.30 — 50

9.0 – — — 21.30 509.2 – — — 26.70 — 509.4 -- — — — — — 509.6 — — — — 36.85 — 509.8 -- — — 40.80 50

10.0 – — — 43.90 50

NOTE — Figures in parentheses belong to the same set.

12

1S 15557:2005

ANNEX C

(Foreword,)

COMMITTEE COMPOSITION

Inorganic Chemicals and Photographic Materials Sectional Committee, CHD 1

Organization

Central Salt and Marine Chemicals Research Institute (CSMCRI),Bhavnagar

Alkali Manufacturers’ Association of India, New Delhi

Balhirpur Industries Limited, Uttar Kannaca

Bharat Electronics Limited, Bangalore

Central Electrochemical Research Institute, Karaikudi

Central Salt and Marine Chemicals Research Institute (CSMCRI),Bhavnagar

Central South Gujarat Salt Manufacturers’ Association, Bhamch,Gujarat

Chemplast Saamar Limited, Mettur Dam, Tamil Nadu

Dharamsi MorarjiChemicalCo Ltd,Ambemath

GeologicalSurveyof India,Kolkata

Golden Chemicals Limited, Mumbai

Gujarat Alkalies and Chemicals Ltd, Vadodara

Hindustan Lever Ltd, Mumbai

Hindrrstrm Photo Films Manufacturing Co Ltd, Ootacamund

Indian Chemicals Manufacturers’ Association, Mumbai

Indm Institute for Chemical Technology, Hyderabad

Mmk.lry of Defence (DGQA), Kanpur

Ministry of Defence (R & D), New Delhi

National Chemical Laboratory, Pune

National Mhrersd Development Corporation, Hyderabad

National Physical Laboratory, New Delhi

National Test House, Kolkata

OffIce of Development Commissioner, Small Scale Industries,New Delhl

RDSO, Lucknow’

Ronuk Industries Ltd, Mumbai

Saumshtra Chemicals, Porbandar

Shriram Institute for IndustrialResearch,Delhi

Standard Alkali (Chemical Division), Mumbai

Representative(s)

h P. K. GHOSH (Chairman)

Srmrwm HARIEETKAUR ANAND

DRV. V. SAVANTDRR. S. RAMACHANDRA(Alternate)

SHKIN. IUVI BHUSAN

DRR. C. Smm (Alternate)

DR(SHRJMATJ) SOBHAJAYAKRJSHNAN

DR R. S. SHUKLA

Sma PARA(i Swsm-r

Smu M. SIVASUBRAiWANrA?4

Wra H. V. RAO

DR S. P. BHATTACHARYA(Alternate)

DR D. K. DASDR SUBHASHCHANORA(Alternate)

DR P. G. PRADHAN

SHRI VIJAY HOLIHOSOUR(Alternate)

SHRI H. G, NAIK

DR V. KRJSHNAN

DR A. PRAMANIK(Alternate)

SHRI ANAND HIPPALGAONKAR

Ri3pitEsENTATJvE

FLEP=sENT.4TivE

SHRJ s. s. RAoSmu R. S. DIWAKAR{Alternate)

COL J. C. MEJITA

DR A. A. NATU

Ssrru M. PRASAD

SrmI N. C. LAKM-hdAN(A/ternate)

DR A. K. AGARWALDR PRABHATK. GUPTA(Alternate)

DR S. RAHUT ‘

DR Y. C. NUHAWAN(Alternate)

Smu S. P. SINGHDR J. S. I&xm (Alternate)

REPRESENTATJVE

SHRJMATIR. K. SHAH

SHJU S. C. SHARMA

Smu M. M. NIGAM(Alternate)

SJUUMATILAXMI RAWATSHRI B, GOBINDANNAIR (Alternate)

Smu V. K. KAPUR

Smu S. N. S. Gmu(Alternate)

13

1S 15557:2005

Organization

Tarnilnadu Petroproducts Ltd, Chennai

Tata Chemicals Ltd, Mithapur

BIS Directorate General

Representative(s)

Cn HANUMANTHARAO

DR D. D. KUMTA

SHRI U. C. SHRIVASTAVA, Director and Head (CHD)[Representing Director General (fi-oficio)]

MemberSecretarySHRI P. GHOSH

Director (CHD), 91S

Analytical Method Validation for Inorganic Chemicals Subcommittee, CHD 1 :,1

National Chemical Laboratory, Pune

Bhabha Atomic Research Centre, Mumbai

Central Indian Pharmacopoeia Laboratory, Ghaziabad

Central Salt and Marine Chemicals Research Institute (CSMCRI),Bhavnagar

Hindustan LeverLimited,Mumbai

IndianInstituteof ChemicalTechnology,Hyderabad

IndianStatisticalInstitute,Kolkata

ltalab(P) Ltd, Mumbai

National Metallurgical Laboratory, Jamshedpur

National Physical Laboratory, New Delhi

National Test House, Kolkata

SGS India Pvt Ltd, Gurgaon

Shriram Institute of Industrial Research, Delhi

S]CART, Ahmedabad

Y’imta Laboratory, Hyderabad

DR A. A. NATO (Convener)

DR M. SUOERSANAN

DR RAMAN M. SINGH

Saru P. S. MANOAL (Mternare)

REPRESENTATIVE

DR V. KRISHNAN

DR G. S. R. SASTRY

DR A. S. R. KIUSHNAMURTHY(A1/ernafe)

DR S. R. MOHAFI

DR ARVINO SETH (Alternate)

Smu AVINASH S. KAMBLI

SHRS K. K. GUPTA

DR N. N. DAS (Alternate)

DR A. K. AGARWAL

RI?PWSENTATSVE

DR JASVIR SINGH

Statr S. K. MA- (Alternate)

.%numn LAXMSIUWAT

Smu B. GOWNOAN NAIR (Alternate)

REPRESENTATIVE

R13PRSSENTATIVE

14

Bureau of Indian Standards

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Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standardsshould ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of‘BIS Catalogue’ and ‘Standards : Monthly Additions’.

This Indian Standard has been developed from Doc ~No. CHD 1 (1 194).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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