ISO 3771:1994
(Main)Petroleum products — Determination of base number — Perchloric acid potentiometric titration method
Petroleum products — Determination of base number — Perchloric acid potentiometric titration method
Cancels and replaces the first edition (1977). Establishes a method for the determination of basic constituents in petroleum products by potentiometric titration with perchloric acid in glacial acetic acid. Two variations of the method are described, using different titration solvent volumes and test sample masses. The ranges of base number values for which precision values for the method have been established are: unused oils - base numbers from 6 to 70; additive concentrates - base numbers from 5 to 300; used oils on which were employed the forward titrations - base numbers from 5 to 27.
Produits pétroliers — Détermination de l'indice de base — Méthode par titrage potentiométrique à l'acide perchlorique
Naftni proizvodi - Določanje baznega števila - Metoda potenciometrične titracije s perklorovo kislino
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INTERNATIONAL
Is0
STANDARD
3771
Second edition
1994-08-15
Petroleum products
- Determination of
base number - Perchloric acid
potentiometric titration method
Produits p&roliers
- Dbtermination de I ’indice de base - M6thode par
titrage potentiom&rique B I ’acide perchlorique
Reference number
IS0 3771 :I 994(E)
---------------------- Page: 1 ----------------------
IS0 3771:1994(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(I EC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 3771 was prepared by Technical Committee
lSO/TC 28, Petroleum products and lubricants.
This second edition cancels and replaces the first edition
(IS0 3771:1977), which has been technically revised.
0 IS0 1994
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
---------------------- Page: 2 ----------------------
INTERNATIONAL STANDARD 0 IS0 IS0 3771:1994(E)
Petroleum products - Determination of base
number - Perchloric acid potentiometric titration
method
- The use of this International Standard may involve hazardous materials, operations
WARNING
and equipment. This standard does not purport to address all of the safety problems associated
with its use. It is the responsibility of the user of this standard to establish appropriate safety and
health practices and determine the applicability of regulatory limitations prior to use.
these oils, and of service conditions of the oils. Neverthe-
1. Scope
less it was not possible to cover the complete range of base
numbers. It is reasonable to suppose that interpolation
This International Standard specifies a method for the
within and extrapolation, from the ranges actually tested will
determination of basic constituents in petroleum
not introduce serious errors in the precision.
products by potentiometric titration with perchloric
acid in glacial acetic acid.
2 Normative references
The constituents that may be considered to have
The following standards contain provisions which,
basic characteristics include organic and inorganic
through reference in this text, constitute provisions
bases, amino compounds, salts of weak acids (for
of this International Standard. At the time of publi-
example soaps), basic salts of polyacid bases, and
cation, the editions indicated were valid. All standards
salts of heavy metals.
are subject to revision, and parties to agreements
Two variations of the method are described, Pro-
based on this International Standard are encouraged
cedures A and B, using different titration solvent vol-
to investigate the possibility of applying the most re-
umes and test sample masses.
cent editions of the standards indicated below.
Members of IEC and IS0 maintain registers of cur-
Round-robin tests on a series of unused and
NOTE 1
rently valid International Standards.
used oils and additive concentrates have shown the Pro-
cedures A and B to give statistically equivalent results.
IS0 385-l :1984, Laboratory glassware - Burettes -
Part 1: General requirements.
The ranges of base number values for which precision
values for the method have been established are:
IS0 3696: 1987, Water for analytical laboratory use -
Specification and test methods.
unused oils - base numbers from 6 to 70;
additive concentrates - base numbers from 5 to 300;
3 Definition .
used oils on which were employed the forward
For the purposes of this International Standard, the
titration - base numbers from 5 to 27.
following definition applies.
NOTE 2 During the development of the original test
3.1 base number: The quantity of perchloric acid,
method (Procedure A) and the test method using reduced
expressed in terms of the equivalent number of milli-
titration solvent volume (Procedure B), cooperative testing
grams of potassium hydroxide, required to titrate 1 g
was done on samples covering a wide range of types of
oils, of additive concentrates which are used to prepare of sample dissolved in the specified solvent to a.
---------------------- Page: 3 ----------------------
IS0 3771:1994(E) 0 IS0
well-defined inflection point as specified in this Inter-
5.7 Titration solvent.
national Standard.
Add 1 volume of acetic acid (5.1) to 2 volumes of
chlorobenzene (5.3).
4 Principle
5.8 Perchloric acid, HCl04, 0,l mol/l standard
4.1 The test sample is dissolved in an essentially
volumetric acetous solution.
anhydrous mixture of chlorobenzene and glacial acetic
acid and titrated with a standard volumetric solution
of perchloric acid in glacial acetic acid using a
5.8.1 Preparation
potentiometric titrimeter. A glass indicating electrode
and a calomel reference electrode are used, the latter
Either mix 8,5 ml of perchloric acid (70 % to 72 %
being connected with the test sample solution by
mass fraction) with 500 ml of acetic acid (5.1) and
means of a salt bridge. The meter readings are plotted
30 ml of acetic anhydride (5.2) or, if the titrant is pre-
against the corresponding volumes of titrating sol-
pared using 60 % to 62 % mass fraction perchloric
ution, and the endpoint is taken as the last inflection
acid, use 10,2 ml of 60 % to 62 % mass fraction per-
in the resulting cun/e.
chloric acid and 38 ml of acetic anhydride or, if the
titrant is prepared using 57 % mass fraction perchloric
acid, use 11,8 ml of 57 % mass fraction perchloric
4.2 Procedure A uses 120 ml of titration solvent;
acid and 40 ml of acetic anhydride.
Procedure B uses 60 ml of titration solvent. In ad-
dition, the two procedures use different equations for
Avoid adding excess acetic anhydride to prevent
the calculation of appropriate sample masses. Many
acetylation of any primary or secondary amines which
portions of Procedures A and B are identical. Only the
may be present in the sample under test.
unique portions are described separately for the two
procedures.
Dilute to 1 000 ml with acetic acid (5.1) and allow the
solution to stand 24 h before standardization.
4.3 Occasionally certain used oils give no inflection
when titrated according to 4.1, in which case back-
5.8.2 Standardization
titration with a standard volumetric acetous sodium
acetate solution titrant is carried out (see clause 11).
5.8.2.1 Procedure A
Dry a quantity of potassium hydrogen phthalate (5.4)
5 Reagents
in an oven at 120 “C for 2 h and allow it to cool. Take
0,l g to 0,2 g of the potassium hydrogen phthalate
During the analysis, use only reagents of recognized
analytical grade, and water equivalent to Grade 3 of weighed to the nearest 0,l mg, and dissolve it with
IS0 3696. care in 40 ml of warm acetic acid (5.1). Add 80 ml of
chlorobenzene (5.3), cool, and titrate with the per-
chloric acid solution (5.8.1), using the electrode sys-
5.1 Acetic acid, CH&OOH, glacial.
tem and procedures given in 8.1 to 8.4 and 9.4.
Detect the endpoint by the same procedure used for
5.2 Acetic anhydride, (CH3-CO)zO.
the base number determination (see 10.2). Carry out
a blank titration on 40 ml of acetic acid plus 80 ml of
chlorobenzene (see 9.6).
5.3 Chlorobenzene, CGH5CI.
5.8.2.2 Procedure B
5.4 Potassium hydrogen phthalate, KHCaH404.
Dry a quantity of potassium hydrogen phthalate (5.4)
5.5 Sodium carbonate, Na2C03, anhydrous.
in an oven at 120 “C for 2 h and allow it to cool. Take
0,05 g to 0,l g of the potassium hydrogen phthalate
weighed to the nearest 0,l mg and dissolve it with
5.6 Sodium perchlorate, NaCl04, electrolyte.
care in 20 ml of warm acetic acid (5.1). Add 40 ml of
Prepare a saturated solution of sodium perchlorate in chlorobenzene (5.31, cool, and titrate with the per-
the acetic acid (5.1). An excess of undissolved sodium chloric acid solution (5.8.1) as described in 5.8.2.1.
perchlorate shall always be present at the bottom of Carry out a blank titration on 20 ml of acetic acid plus
the solution. 40 ml of chlorobenzene (see 9.6).
2
---------------------- Page: 4 ----------------------
0 IS0
IS0 3771:1994(E)
5.8.3 Calculation of concentration 5.9.3 Calculation of concentration
Calculate the concentration, Co, in moles per litre, of Calculate the concentration, C,, in moles per litre, of
the perchloric acid solution from the formula: sodium acetate from the formulae:
1 OOOm
@too - Vo> Co
co = . . .
=
(1) . . . (2)
C for Procedure A
1
204,23 (V, - Vo)
Y2
where (400 - Vo) co
c, = for Procedure B . . . (3)
v2
m is the mass, in grams, of potassium hy-
drogen phthalate;
where
is the numerical value of the volume, in
VO and V. are as defined for equation (I);
CO
millilitres, of perchloric acid solution used
for the blank titration; is the numerical value of the volume, in
v2
millilitres, of sodium acetate (5.9) used in
is the numerical value of the volume, in
5 the standardization.
millilitres, of perchloric acid solution used
for the titration. Restandardize the sodium acetate solution at least
once a week, or more often if there is any reason to
Because of the relatively large coefficient of cubic
suspect that the concentration has changed.
expansion of organic liquids, use the acetous per-
chloric acid solution either within 5 “C of the tem-
5.10 Cleaning solution, strongly oxidizing acid, e.g.
perature at which it was standardized or, if used at a
chromiumsulfuric acid.
temperature more than 5 “C higher, multiply the vol-
ume used by the factor [I - (t x O,OOl)], or if used at
WARNING - When using chromiumsulfuric acid
a temperature more than 5 “C lower, multiply by the
cleaning solution, eye protection and protective
factor [I + (t x O,OOl)], where t is the difference, in
clothing are essential. Never pipette the cleaning
degrees Celsius, between the temperatures of stan-
solution by mouth. After use, do not pour cleaning
dardization and use (and is always positive).
solutions down the drain, but neutralize them
with great care owing to the concentrated sulfuric
Restandardize the perchloric acid solution at least
acid present, and dispose of them in accordance
once a week, or more often if there is any reason to
with standard procedures for toxic laboratory
suspect that the concentration has changed.
waste (chromium is highly dangerous to the en-
vironment).
5.9 Sodium acetate, NaC2H302, 0,l mol/l standard
volumetric acetous solution.
6 Apparatus
5.9.1 Preparation
Ordinary laboratory apparatus, and in particular the
Dissolve 5,3 g of anhydrous sodium carbonate (5.5) in
following are required.
300 ml of acetic acid (5.1). Dilute to 1 I with acetic
acid after dissolution is complete.
6.1 Potentiometric titrimeter, either automatic re-
cording or manual.
5.9.2 Standardization
6.2 Glass electrode, pH 0 to pH 11, general-
5.9.2.1 Procedure A
purpose type.
Use 120 ml of titration solvent (5.7) and 8,00 ml of the
perchloric acid solution (5.8). Titrate with sodium
6.3 Reference electrode, sleeve-type saturated
acetate solution (5.9) using the electrode system and
calomel electrode with non-aqueous salt bridge as
procedure given in 8.1 to 8.4 and 9.4. Detect the
described in clause 8.
endpoint by the same procedure used for the base
number determination (see 10.2).
Some reference electrodes with fritted or fibre
NOTE 3
diaphragms and some combined glass plus reference
5.9.2.2 Procedure B electrode systems are commercially available, such as the
single-rod glass plus silver/silver chloride electrode as-
Use 60 ml of titration solvent (5.7) and 4,00 ml of
sembly. During the development of this method, the use
perchloric acid (5.8). Titrate as described in 5.9.2.1. of electrodes of these types gave problems in some lab-
3
---------------------- Page: 5 ----------------------
IS0 3771:1994(E)
oratories, but not in others. Accordingly, these electrodes
8 Preparation of electrode system
are permitted in this method, provided that the sodium
perchlorate bridge is used; however, if stability or other
problems arise with their use, the sleeve-type electrode
8.1 Preparation of electrodes
should be used.
If the calomel electrode (6.3) is to be changed from
aqueous bridge to non-aqueous, drain out the
6.4 Stirrer, either mechanical or electrical, with
aqueous solution, wash out crystals of potassium
variable speeds and with propeller or paddle of
chloride with water, then rinse the outer jacket (salt
chemically inert material.
bridge) several times with the sodium perchlorate
electrolyte (5.6). Finally, fill the outer jacket with the
If an electrical stirrer is used, it shall be grounded
sodium perchlorate electrolyte up to the filling hole.
(earthed) so that disconnecting or connecting the
When using the sleeve-type electrode, carefully re-
power to the motor will not produce a permanent
move the ground-glass sleeve and thoroughly wipe
change in meter reading during the course of a
both ground-glass surfaces. Replace the sleeve
titration. A magnetic stirrer with stirring bar may be
loosely and allow a few drops of electrolyte to drain
used provided that it meets the above conditions.
through to flush the ground-glass joint and to wet the
ground surfaces thoroughly with electrolyte. Set the
6.5 Burette, manual or automatic, conforming to the
sleeve firmly in place, refill the outer jacket with the
requirements of IS0 385-1, 10 ml or 20 ml capacity,
sodium perchlorate electrolyte and rinse the electrode
graduated in 0,05 ml divisions, calibrated with an ac-
with chlorobenzene (5.3). When in use, keep the
curacy of + 0,02 ml.
- electrolyte level in the calomel electrode above that
of the liquid in the titration beaker (6.6) to prevent
entry of contaminants in the salt bridge. When not in
6.6 Titration beaker, tall-form, made of borosilicate
use, fill the calomel electrode with sodium perchlorate
glass or plastic that is inert to the reagents listed in
e
...
SLOVENSKI STANDARD
SIST ISO 3771:1996
01-december-1996
1DIWQLSURL]YRGL'RORþDQMHED]QHJDãWHYLOD0HWRGDSRWHQFLRPHWULþQHWLWUDFLMHV
SHUNORURYRNLVOLQR
Petroleum products -- Determination of base number -- Perchloric acid potentiometric
titration method
Produits pétroliers -- Détermination de l'indice de base -- Méthode par titrage
potentiométrique à l'acide perchlorique
Ta slovenski standard je istoveten z: ISO 3771:1994
ICS:
75.080 Naftni proizvodi na splošno Petroleum products in
general
SIST ISO 3771:1996 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 3771:1996
---------------------- Page: 2 ----------------------
SIST ISO 3771:1996
INTERNATIONAL
Is0
STANDARD
3771
Second edition
1994-08-15
Petroleum products
- Determination of
base number - Perchloric acid
potentiometric titration method
Produits p&roliers
- Dbtermination de I ’indice de base - M6thode par
titrage potentiom&rique B I ’acide perchlorique
Reference number
IS0 3771 :I 994(E)
---------------------- Page: 3 ----------------------
SIST ISO 3771:1996
IS0 3771:1994(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for
which a technical committee has been established has the right to be
represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(I EC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 3771 was prepared by Technical Committee
lSO/TC 28, Petroleum products and lubricants.
This second edition cancels and replaces the first edition
(IS0 3771:1977), which has been technically revised.
0 IS0 1994
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
---------------------- Page: 4 ----------------------
SIST ISO 3771:1996
INTERNATIONAL STANDARD 0 IS0 IS0 3771:1994(E)
Petroleum products - Determination of base
number - Perchloric acid potentiometric titration
method
- The use of this International Standard may involve hazardous materials, operations
WARNING
and equipment. This standard does not purport to address all of the safety problems associated
with its use. It is the responsibility of the user of this standard to establish appropriate safety and
health practices and determine the applicability of regulatory limitations prior to use.
these oils, and of service conditions of the oils. Neverthe-
1. Scope
less it was not possible to cover the complete range of base
numbers. It is reasonable to suppose that interpolation
This International Standard specifies a method for the
within and extrapolation, from the ranges actually tested will
determination of basic constituents in petroleum
not introduce serious errors in the precision.
products by potentiometric titration with perchloric
acid in glacial acetic acid.
2 Normative references
The constituents that may be considered to have
The following standards contain provisions which,
basic characteristics include organic and inorganic
through reference in this text, constitute provisions
bases, amino compounds, salts of weak acids (for
of this International Standard. At the time of publi-
example soaps), basic salts of polyacid bases, and
cation, the editions indicated were valid. All standards
salts of heavy metals.
are subject to revision, and parties to agreements
Two variations of the method are described, Pro-
based on this International Standard are encouraged
cedures A and B, using different titration solvent vol-
to investigate the possibility of applying the most re-
umes and test sample masses.
cent editions of the standards indicated below.
Members of IEC and IS0 maintain registers of cur-
Round-robin tests on a series of unused and
NOTE 1
rently valid International Standards.
used oils and additive concentrates have shown the Pro-
cedures A and B to give statistically equivalent results.
IS0 385-l :1984, Laboratory glassware - Burettes -
Part 1: General requirements.
The ranges of base number values for which precision
values for the method have been established are:
IS0 3696: 1987, Water for analytical laboratory use -
Specification and test methods.
unused oils - base numbers from 6 to 70;
additive concentrates - base numbers from 5 to 300;
3 Definition .
used oils on which were employed the forward
For the purposes of this International Standard, the
titration - base numbers from 5 to 27.
following definition applies.
NOTE 2 During the development of the original test
3.1 base number: The quantity of perchloric acid,
method (Procedure A) and the test method using reduced
expressed in terms of the equivalent number of milli-
titration solvent volume (Procedure B), cooperative testing
grams of potassium hydroxide, required to titrate 1 g
was done on samples covering a wide range of types of
oils, of additive concentrates which are used to prepare of sample dissolved in the specified solvent to a.
---------------------- Page: 5 ----------------------
SIST ISO 3771:1996
IS0 3771:1994(E) 0 IS0
well-defined inflection point as specified in this Inter-
5.7 Titration solvent.
national Standard.
Add 1 volume of acetic acid (5.1) to 2 volumes of
chlorobenzene (5.3).
4 Principle
5.8 Perchloric acid, HCl04, 0,l mol/l standard
4.1 The test sample is dissolved in an essentially
volumetric acetous solution.
anhydrous mixture of chlorobenzene and glacial acetic
acid and titrated with a standard volumetric solution
of perchloric acid in glacial acetic acid using a
5.8.1 Preparation
potentiometric titrimeter. A glass indicating electrode
and a calomel reference electrode are used, the latter
Either mix 8,5 ml of perchloric acid (70 % to 72 %
being connected with the test sample solution by
mass fraction) with 500 ml of acetic acid (5.1) and
means of a salt bridge. The meter readings are plotted
30 ml of acetic anhydride (5.2) or, if the titrant is pre-
against the corresponding volumes of titrating sol-
pared using 60 % to 62 % mass fraction perchloric
ution, and the endpoint is taken as the last inflection
acid, use 10,2 ml of 60 % to 62 % mass fraction per-
in the resulting cun/e.
chloric acid and 38 ml of acetic anhydride or, if the
titrant is prepared using 57 % mass fraction perchloric
acid, use 11,8 ml of 57 % mass fraction perchloric
4.2 Procedure A uses 120 ml of titration solvent;
acid and 40 ml of acetic anhydride.
Procedure B uses 60 ml of titration solvent. In ad-
dition, the two procedures use different equations for
Avoid adding excess acetic anhydride to prevent
the calculation of appropriate sample masses. Many
acetylation of any primary or secondary amines which
portions of Procedures A and B are identical. Only the
may be present in the sample under test.
unique portions are described separately for the two
procedures.
Dilute to 1 000 ml with acetic acid (5.1) and allow the
solution to stand 24 h before standardization.
4.3 Occasionally certain used oils give no inflection
when titrated according to 4.1, in which case back-
5.8.2 Standardization
titration with a standard volumetric acetous sodium
acetate solution titrant is carried out (see clause 11).
5.8.2.1 Procedure A
Dry a quantity of potassium hydrogen phthalate (5.4)
5 Reagents
in an oven at 120 “C for 2 h and allow it to cool. Take
0,l g to 0,2 g of the potassium hydrogen phthalate
During the analysis, use only reagents of recognized
analytical grade, and water equivalent to Grade 3 of weighed to the nearest 0,l mg, and dissolve it with
IS0 3696. care in 40 ml of warm acetic acid (5.1). Add 80 ml of
chlorobenzene (5.3), cool, and titrate with the per-
chloric acid solution (5.8.1), using the electrode sys-
5.1 Acetic acid, CH&OOH, glacial.
tem and procedures given in 8.1 to 8.4 and 9.4.
Detect the endpoint by the same procedure used for
5.2 Acetic anhydride, (CH3-CO)zO.
the base number determination (see 10.2). Carry out
a blank titration on 40 ml of acetic acid plus 80 ml of
chlorobenzene (see 9.6).
5.3 Chlorobenzene, CGH5CI.
5.8.2.2 Procedure B
5.4 Potassium hydrogen phthalate, KHCaH404.
Dry a quantity of potassium hydrogen phthalate (5.4)
5.5 Sodium carbonate, Na2C03, anhydrous.
in an oven at 120 “C for 2 h and allow it to cool. Take
0,05 g to 0,l g of the potassium hydrogen phthalate
weighed to the nearest 0,l mg and dissolve it with
5.6 Sodium perchlorate, NaCl04, electrolyte.
care in 20 ml of warm acetic acid (5.1). Add 40 ml of
Prepare a saturated solution of sodium perchlorate in chlorobenzene (5.31, cool, and titrate with the per-
the acetic acid (5.1). An excess of undissolved sodium chloric acid solution (5.8.1) as described in 5.8.2.1.
perchlorate shall always be present at the bottom of Carry out a blank titration on 20 ml of acetic acid plus
the solution. 40 ml of chlorobenzene (see 9.6).
2
---------------------- Page: 6 ----------------------
SIST ISO 3771:1996
0 IS0
IS0 3771:1994(E)
5.8.3 Calculation of concentration 5.9.3 Calculation of concentration
Calculate the concentration, Co, in moles per litre, of Calculate the concentration, C,, in moles per litre, of
the perchloric acid solution from the formula: sodium acetate from the formulae:
1 OOOm
@too - Vo> Co
co = . . .
=
(1) . . . (2)
C for Procedure A
1
204,23 (V, - Vo)
Y2
where (400 - Vo) co
c, = for Procedure B . . . (3)
v2
m is the mass, in grams, of potassium hy-
drogen phthalate;
where
is the numerical value of the volume, in
VO and V. are as defined for equation (I);
CO
millilitres, of perchloric acid solution used
for the blank titration; is the numerical value of the volume, in
v2
millilitres, of sodium acetate (5.9) used in
is the numerical value of the volume, in
5 the standardization.
millilitres, of perchloric acid solution used
for the titration. Restandardize the sodium acetate solution at least
once a week, or more often if there is any reason to
Because of the relatively large coefficient of cubic
suspect that the concentration has changed.
expansion of organic liquids, use the acetous per-
chloric acid solution either within 5 “C of the tem-
5.10 Cleaning solution, strongly oxidizing acid, e.g.
perature at which it was standardized or, if used at a
chromiumsulfuric acid.
temperature more than 5 “C higher, multiply the vol-
ume used by the factor [I - (t x O,OOl)], or if used at
WARNING - When using chromiumsulfuric acid
a temperature more than 5 “C lower, multiply by the
cleaning solution, eye protection and protective
factor [I + (t x O,OOl)], where t is the difference, in
clothing are essential. Never pipette the cleaning
degrees Celsius, between the temperatures of stan-
solution by mouth. After use, do not pour cleaning
dardization and use (and is always positive).
solutions down the drain, but neutralize them
with great care owing to the concentrated sulfuric
Restandardize the perchloric acid solution at least
acid present, and dispose of them in accordance
once a week, or more often if there is any reason to
with standard procedures for toxic laboratory
suspect that the concentration has changed.
waste (chromium is highly dangerous to the en-
vironment).
5.9 Sodium acetate, NaC2H302, 0,l mol/l standard
volumetric acetous solution.
6 Apparatus
5.9.1 Preparation
Ordinary laboratory apparatus, and in particular the
Dissolve 5,3 g of anhydrous sodium carbonate (5.5) in
following are required.
300 ml of acetic acid (5.1). Dilute to 1 I with acetic
acid after dissolution is complete.
6.1 Potentiometric titrimeter, either automatic re-
cording or manual.
5.9.2 Standardization
6.2 Glass electrode, pH 0 to pH 11, general-
5.9.2.1 Procedure A
purpose type.
Use 120 ml of titration solvent (5.7) and 8,00 ml of the
perchloric acid solution (5.8). Titrate with sodium
6.3 Reference electrode, sleeve-type saturated
acetate solution (5.9) using the electrode system and
calomel electrode with non-aqueous salt bridge as
procedure given in 8.1 to 8.4 and 9.4. Detect the
described in clause 8.
endpoint by the same procedure used for the base
number determination (see 10.2).
Some reference electrodes with fritted or fibre
NOTE 3
diaphragms and some combined glass plus reference
5.9.2.2 Procedure B electrode systems are commercially available, such as the
single-rod glass plus silver/silver chloride electrode as-
Use 60 ml of titration solvent (5.7) and 4,00 ml of
sembly. During the development of this method, the use
perchloric acid (5.8). Titrate as described in 5.9.2.1. of electrodes of these types gave problems in some lab-
3
---------------------- Page: 7 ----------------------
SIST ISO 3771:1996
IS0 3771:1994(E)
oratories, but not in others. Accordingly, these electrodes
8 Preparation of electrode system
are permitted in this method, provided that the sodium
perchlorate bridge is used; however, if stability or other
problems arise with their use, the sleeve-type electrode
8.1 Preparation of electrodes
should be used.
If the calomel electrode (6.3) is to be changed from
aqueous bridge to non-aqueous, drain out the
6.4 Stirrer, either mechanical or electrical, with
aqueous solution, wash out crystals of potassium
variable speeds and with propeller or paddle of
chloride with water, then rinse the outer jacket (salt
chemically inert material.
bridge) several times with the sodium perchlorate
electrolyte (5.6). Finally, fill the outer jacket with the
If an electrical stirrer is used, it shall be grounded
sodium perchlorate electrolyte up to the filling hole.
(earthed) so that disconnecting or connecting the
When using the sleeve-type electrode, carefully re-
power to the motor will not produce a permanent
move the ground-glass sleeve and thoroughly wipe
change in meter reading during the course of a
both ground-glass surfaces. Replace the sleeve
titration. A magnetic stirrer with stirring bar may be
loosely and allow a few drops of electrolyte to drain
used provided that it meets the above conditions.
through to flush the ground-glass joint and to wet the
ground surfaces thoroughly with electrolyte. Set the
6.5 Burette, manual or automatic, conforming to the
sleeve firmly in place, refill the outer jacket with the
requirem
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