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Ref. No. : ISO/R 997-1969(E)
IS0
I N T E RN AT I ON A L O R G A N IZAT I ON FO R STA N DA RD IZATl O N
IS0 RECOMMENDATION
R 997
POTASSIUM HYDROXIDE FOR INDUSTRIAL USE
DETERMINATION OF CALCIUM
EDTA COMPLEXOMETRIC METHOD
1st EDITION
February 1969
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 997, Potassium hydroxide for industrial use - Determination of calcium -
EDTA complexometric method, was drawn up by Technical Committee ISO/TC 47, Chemistry, the Secretariat
of which is held by the Ente Nazionale Italian0 di Unificazione (UNI).
Work on this question led, in 1966, to the adoption of a Draft IS0 Recommendation.
In December 1966, this Draft IS0 Recommendation (No. 1106) was circulated to all the IS0 Member
L.
Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature, by the following
Member Bodies .
Austria Israel Spain
Belgium Italy Switzerland
Brazil Japan Thailand
Chile Netherlands Turkey
Czechoslovakia New Zealand U.A.R.
Poland United Kingdom
Germany
Hungary Portugal U .S.S.R.
India Romania Yugoslavia
Ireland South Africa, Kep. of
Two Member Bodies opposed the approval of the Draft :
France
U.S.A.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council, which
decided, in February 1969, to accept it as an IS0 RECOMMENDATION.
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ISO/R 997- 1969(E)
February 1969
IS0 Recommendation R 997
POTASSIUM HYDROXIDE FOR INDUSTRIAL USE
DETERMINATION OF CALCIUM
EDTA COMPLEXOMETRIC METHOD
1. SCOPE
This IS0 Recommendation describes a complexometric method for the determination of calcium in potassium
hydroxide for industrial use.
2. PRINCIPLE
Titration with disodium ethylenediaminetetracetate in the presence of glyoxal bis (2-hydroxy-anil) as indicator,
after elimination of impurities which may hinder the determination.
3. REAGENTS
Distilled water or water of equivalent purity should be used in the test.
3.1 Hydrochloric acid, approximately d = 1.19, 38 (mlm) or 12 N solution.
3.2 Hydrochloric acid, approximately d = 1.035, 7 (m/m) or 2 N solution.
Addsome water to 165 ml of the approximately d = 1 .i9 hydrochloric acid solution and dilute to 1000 ml.
3.3 Sulphuric acid, approximately d = 1.06, 9 (m/m) or 2 N solution.
Add 55 ml of approximately d = 1.83 sulphuric acid solution to some water, allow to cool and dilute to
1 O00 mi.
3.4 Sodium hydroxide, approximately d = 1.08, 7.5 (mlm) or 2 N solution.
Dissolve 80 g of sodium hydroxide in water and dilute to 1000 ml.
Ammonium hydroxide, approximately d = 0.983, 3.5 'lo (mlm) or 2 N solution.
3.5
Add some water to 250 ml of approximately d = 0.94 ammonium hydroxide (14.5 'lo (m/m) or 8 N
solution approximately) and dilute to 1000 rnl.
3.6 Iron (III) chloride, hydrochloric solution containing approximately 2 g/l of Fe.
Weigh, to the nearest O. 1 g, 1 O g of crystals of iron (III) chloride hexahydrate. Place in a 1 O00 ml one-mark
volumetric flask and dissolve in approximately 600 ml of water.
Add 10 ml of the hydrochloric acid solution (3.1). Dilute to the mark and mix thoroughly.
3.7 Sodium sulphide, saturated solution.
Prepare a solution using crystals of sodium sulphide hydrate (Naz S.9Hz O) previously washed with water.
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ISO/R Y97-1969(E
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3.8 Ethanol, 95 "lo (vlv).
Alternatively, alcohol denatured with acetone, but not coloured, may be used.
3.9 Calcium chloride, 0.02 M standard solution.
Weigh, to the nearest 0.001 g, 2.002 g of precipitated calcium carbonate (CaC03) and place in a 600 ml
beaker. Mix 75 ml of water with 25 ml of the hydrochloric acid solution (3.2) and transfer this solution to
the beaker. Boil for about 5 minutes to eliminate carbon dioxide. Cool to about 20 OC, transfer quantita-
tively to a 1000 ml one-mark volumetric flask, dilute to the mark and mix thoroughly.
3.10 Disodium ethylenediaminetetracetate (EDTA), 0.002 M standard volumetric solution.
Dissolve approximately 7.7 g of EDTA in water.
Transfer quantitatively to a 1000 ml one-mark volumetric flask, dilute to the mark and mix thoroughly.
Adjust the concentration of this solution to 0.02 M exactly, calculated on the calcium chloride standard
solution (3.9), operating as follows :
Transfer 25.0 ml of the calcium chloride solution (3.9) to a 250 ml conical flask.
Successively add approximately 25 ml of water, then, by means of graduated pipettes, 4 ml of the sodium
hydroxide solution (3.4), 15 ml of ethanol (3.8) and 1 .O ml of the glyoxal bis (2-hydroxy-anil) solution
(3.12). Wait for about 1 minute, then titrate with the solution whose strength is to be determined, until the
colour turns from red to pure
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