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SLOVENSKI STANDARD
01-julij-2022
Nadomešča:
SIST EN 12125:2013
Kemikalije, ki se uporabljajo za pripravo pitne vode - Natrijev tiosulfat
Chemicals used for treatment of water intended for human consumption - Sodium
thiosulfate
Produkte zur Aufbereitung von Wasser für den menschlichen Gebrauch -
Natriumthiosulfat
Produits chimiques utilisés pour le traitement de l'eau destinée à la consommation
humaine - Thiosulfate de sodium
Ta slovenski standard je istoveten z: EN 12125:2022
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 Kemikalije za čiščenje vode Chemicals for purification of
water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 12125
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2022
EUROPÄISCHE NORM
ICS 71.100.80 Supersedes EN 12125:2012
English Version
Chemicals used for treatment of water intended for human
consumption - Sodium thiosulfate
Produits chimiques utilisés pour le traitement de l'eau Produkte zur Aufbereitung von Wasser für den
destinée à la consommation humaine - Thiosulfate de menschlichen Gebrauch - Natriumthiosulfat
sodium
This European Standard was approved by CEN on 27 March 2022.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12125:2022 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Description . 5
4.1 Identification . 5
4.2 Commercial form . 6
4.3 Physical properties . 6
4.4 Chemical properties . 7
5 Purity criteria . 7
5.1 General. 7
5.2 Composition of commercial product . 7
5.3 Impurities and main by-products . 7
5.4 Chemical parameters. 7
6 Test methods . 8
6.1 Sampling . 8
6.2 Analyses. 8
7 Labelling – Transportation – Storage . 14
7.1 Means of delivery . 14
7.2 Labelling according to the EU legislation . 14
7.3 Transportation regulations and labelling . 14
7.4 Marking . 14
7.5 Storage . 14
Annex A (informative) General information on sodium thiosulfate . 15
Annex B (normative) General rules relating to safety . 16
Bibliography . 17
European foreword
This document (EN 12125:2022) has been prepared by Technical Committee CEN/TC 164 “Water
supply”, the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by November 2022, and conflicting national standards
shall be withdrawn at the latest by November 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 12125:2012.
In comparison with the previous edition, the following technical modifications have been made:
a) Modification of 7.3 on transportation regulations and labelling, adding the sentence “The user must
be aware of the incompatibilities between transported products.”;
b) Modification of 7.4 on marking. The requirements of marking are also applied to the accompanying
documents.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Introduction
In respect of potential adverse effects on the quality of water intended for human consumption caused
by the product covered by this document:
a) this document provides no information as to whether the product may be used without restriction
in any of the Member States of the EU or EFTA;
b) it should be noted that, while awaiting the adoption of verifiable European criteria, existing national
regulations concerning the use and/or the characteristics of this product remain in force.
NOTE Conformity with this document does not confer or imply acceptance or approval of the product in any
of the Member States of the EU or EFTA. The use of the product covered by this document is subject to regulation
or control by National Authorities (see Annex A).
1 Scope
This document is applicable to sodium thiosulfate used for treatment of water intended for human
consumption. It describes the characteristics and specifies the requirements of sodium thiosulfate and
refers to the corresponding analytical methods. It gives information for its use in water treatment.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN ISO 3696, Water for analytical laboratory use - Specification and test methods (ISO 3696)
ISO 3165, Sampling of chemical products for industrial use — Safety in sampling
ISO 5993, Sodium hydroxide for industrial use — Determination of mercury content — Flameless atomic
absorption spectrometric method
ISO 6206, Chemical products for industrial use — Sampling — Vocabulary
ISO 6353-1, Reagents for chemical analysis — Part 1: General test methods
ISO 8213, Chemical products for industrial use — Sampling techniques — Solid chemical products in the
form of particles varying from powders to coarse lumps
ISO 10636, Photography — Processing chemicals — Specifications for anhydrous sodium thiosulfate and
sodium thiosulfate pentahydrate
ISO 22743, Water quality — Determination of sulfates — Method by continuous flow analysis (CFA)
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at
— IEC Electropedia: available at
4 Description
4.1 Identification
4.1.1 Chemical name
Sodium thiosulfate.
4.1.2 Synonym or commons names
Sodium thiosulfate, sodium hyposulfite.
4.1.3 Relative molecular mass
158,11 (anhydrous).
4.1.4 Empirical formula
Na S O .
2 2 3
4.1.5 Chemical formula
Na S O .
2 2 3
4.1.6 CAS-Registry Number
7772-98-7 (anhydrous); 10102-17-7 (pentahydrate).
4.1.7 EINECS reference
231-867-5.
4.2 Commercial form
The product is a crystalline powder.
4.3 Physical properties
4.3.1 Appearance
The hydrated product is colourless crystal. The anhydrous product is a white powder.
4.3.2 Density
3 3
The particle density of the hydrated product is 1,69 g/cm to 1,73 g/cm at 20 °C.
4.3.3 Solubility in water
The solubility of the product in water is 700 g/l at 20 °C (anhydrous); for pentahydrate : 2 910 g/l
at 45 °C.
4.3.4 Vapour pressure
Not applicable.
4.3.5 Boiling point at 100 kPa
Not applicable.
4.3.6 Crystallization point
The product starts to decompose at 45 °C to 50 °C.
4.3.7 Specific heat
Not known.
4.3.8 Viscosity, dynamic
Not applicable.
4.3.9 Critical temperature
Not applicable.
Chemical Abstracts Service Registry Number.
European Inventory of Existing Commercial Chemical Substances.
100 kPa = 1 bar.
4.3.10 Critical pressure
Not applicable.
4.3.11 Physical hardness
Not applicable.
4.4 Chemical properties
The pH value of a diluted aqueous solution of sodium thiosulfate is approximately neutral (6,5 to 8).
Sodium thiosulfate dissolves silver halogenids and other silver salts.
At elevated temperatures (>50 °C), sulfur dioxide is generated.
Sodium thiosulfate releases sulfur dioxide when mixed with acids.
Sodium thiosulfate reacts violently with oxidising agents; e.g. with sodium hypochlorite or hydrogen
peroxide. It shall not come into contact with acids, iodine, lead and silver salts. For additional
information on Sodium thiosulfate, see Annex A.
5 Purity criteria
5.1 General
This document specifies the minimum purity requirements for sodium thiosulfate used for the
treatment of water intended for human consumption. Limits are given for impurities commonly present
in the product. Depending on the raw material and the manufacturing process other impurities may be
present and, if so, this shall be notified to the user and when necessary to relevant authorities.
The national regulations allow users to clarify whether the product is of appropriate purity for the
treatment of water intended for human consumption, taking into account raw water quality, required
dosage, contents of other impurities and additives used in the product and not stated in this document.
Limits have been given for impurities and chemical parameters where these are likely to be present in
significant quantities from the current producti
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