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IS0
I N T ERN AT1 O N A L O RG A NI Z AT1 O N FO R STAN DA RD IZATl ON
IS0 RECOMMENDATION
R 731
FORMIC ACID FOR INDUSTRIAL USE
METHODS OF TEST
1st EDITION
May 1968
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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 73 1, Formic acid for industrial use - Methods of test, 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 by the Technical Committee began in 1956 and led, in 1963, to the
adoption of a Draft IS0 Recommendation.
In December 1964, this Draft IS0 Recommendation (NO. 761) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial nature, by
the following Member Bodies :
Argentina India Romania
Austria Iran South Africa,
Belgium Israel Rep. of
Spain
Bulgaria Italy
Chile Japan Switzerland
Korea, Rep. of Turkey
Czechoslovakia
Netherlands U.A.R.
France
New Zealand United Kingdom
Germany
Greece Poland U.S.S.R.
Portugal Yugoslavia
Hungary
One Member Body opposed the approval of the Draft
U.S.A.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council
which decided, in May 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 731-1968 (E)
IS0 Recommendation R 731 May 1968
FORMIC ACID FOR INDUSTRIAL USE
METHODS OF TEST
1. SCOPE
This IS0 Recommendation describes methods of test for formic acid for industrial use.
2. SAMPLE*
The laboratory sample should be of sufficient size for carrying out all the analysis. It should be
preserved in an air-tight glass-stoppered bottle of such a size that it is nearly filed by the sample.
If it has been necessary to seal the container, care should be taken to avoid the risk of contaminating
the contents in any way.
3. DETERMINATION OF TOTAL ACIDITY
3.1 Principle
Titration of acidity using a standard volumetric solution of sodium hydroxide using phenol-
phthalein as indicator.
3.2 Reagents
Freshly boiled and cooled distilled water or water of equivalent purity should be used in
the test.
3.2.1 Sodium hydroxide, N standard volumetric solution (see Note, clause 3.5).
3.2.2 Phenolphthalein, 5 g/1 ethanolic solution. Dissolve 0.5 g of phenolphthalein in 100 ml of
(v/v) ethanol and make faintly pink by the addition of dilute sodium hydroxide
95
solution.
3.3 Apparatus
Ordinary laboratory apparatus and
3.3.1 Thin glass ampoule, diameter approximately 20 mm (see the Figure). This is only required
for samples believed to contain more than 90 (m/m) of total acidity.
The preparation of an IS0 Recommendation dealing with sampling from the consignment of the products will be
undertaken as soon as the relevant IS0 Technical Committee specifies the general procedure to be followed.
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ISOlR 731 -1968 (E
Dimensions in millimetres
FIGURE - Glass ampoule
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ISO/R 731-1968 (E)
3.4 Procedure
3.4.1 For acids believed to contain more than 90 yo (m/m) of total acidity, expressed as formic
acid.
Weigh the glass ampoule (3.3.1) to the nearest 0.5 mg and introduce a test portion of about
1.5 g by partially immersing the ampoule in the bottle containing the laboratory sample.
Seal the capillary without loss of glass, using the oxidizing flame of the burner; withdraw the
ampoule and invert it. Wipe the end that was immersed in the laboratory sample with a filter
paper and seal rapidly. Weigh the ampoule again to the nearest 0.5 mg and determine to the
nearest milligramme, by difference between the two weighings, the mass of test portion taken.
Place the sealed ampoule in a 250 ml conical flask containing about 50 ml of water. Break up
the ampoule with a glass rod, shake, add 0.5 ml of phenolphthalein solution (3.2.2)and
titrate with the sodium hydroxide solution (3.2.1) to a faint pink end point.
3.4.2 For acids believed to contain less than 90 yo (m/m) of total acidity, expressed as formic acid.
Place a test portion of 1.5 to 2.0 g weighed to the nearest milligramme, into a 250ml
conical flask containing about 50 ml of water. Add 0.5 ml of phenolphthalein solution (3.2.2)
and titrate with the sodium hydroxide solution (3.2.1) to a faint pink end point.
3.5 Expression of results
Total acidity, expressed as formic acid (HCOOH), is given as a percentage by mass by the
following formula :
where
V is the volume, in millilitres, of the N sodium hydroxide solution (3.2.1) used
for the titration,
A is the mass, in grammes, of formic acid (HCOOH) corresponding to 1 ml of N sodium
hydroxide solution.
(Theoretical value 1 ml 2 0.04603 g of HCOOH, see Note below),
E is the mass, in grammes, of the test portion.
NOTE.- If the standard volumetric solution is not of exactly the strength indicated in the list of reagents,
asuitable correction factor should be employed in calculating the results.
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ISO/R 731 -1968 (E)
4. DETERMINATION OF ACIDS OTHER THAN FORMIC ACID
4.1 Field of application
This method is applicable to formic acid containing between 0.5 and 6.0
(m/m) of other
acids calculated as acetic acid.
4.2 Principle
Titration with sodium hydroxide solution using a pH meter, of the acids remaining after
quantitative oxidation of formic acid with excess mercuric oxide.
4.3 Reagents
Freshly boiled and cooled distilled water, or water of equivalent purity should be used in the
test.
4.3.1 Aceticacid, approximately 0.5
(vlv) solution. Dilute 5 ml of glacial acetic acid to 1000 ml.
4.3.2 Mercuric oxide (red).
4.3.3 Sodium hydroxide, 0.1 N standard volumetric solution (see Note, clause 3.5).
4.4 Apparatus
Ordinary laboratory apparatus and
4.4.1 Conical flasks, with ground-glass necks, capacity 250 ml;
4.4.2 Reflux condenser, water cooled. with ground-glass joints to fit the flasks;
4.4.3 pH meter, with a glass electrode.
4.5 Procedure
4.5.1 Test portion
For content of acids other than formic acid less than 2 yo (mfm)
(a)
Weigh 5 g of the laboratory sample (see section 2) to the nearest 0.01 g.
For content of acids other than formic acid 2 yo (mfm) and over
(b)
Weigh 2 g of the laboratory sample (see section 2) to the nearest 0.005 g.
4.5.2 Blank test. At the same time as the analysis, carry out a blank test using the procedure
described in clauses 4.5.3 and 4.5.4 and the same quantities of all reagents.
4.5.3 Preparation of test solution. Place the test portion (4.5.1) in one of the conical flasks (4.4.1).
Add exactly 5.0 ml of acetic acid solution (4.3.1) and an amount of mercuric oxide (4.3.2)
calculated on the basis of 5.5 g of mercuric oxide per gramme of formic acid present in the
test portion. Then add sufficient water to bring the total volume to about 30 ml.
Fit the flask with a condenser (4.4.2) and heat gently for 10 minutes. Fairly strong evolution
of carbon dioxide from the solution containing the test portion occurs. Reflux gently for
30 minutes and rinse the condenser with 20 to 25 ml of water. Cool the flask to room
temperature and pour the contents without fitering into a 250 ml beaker. Rinse the flask into
the beaker with 20 to 25 ml
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