Reference number  
DRS 127 -1: 2018  
© RSB 2018  
 
 
 RWANDA 
STANDARD  DRS 
127-1 
 
Second e dition  
2018 -mm-dd 
 
Bleaching agents — Specification  — 
Part 1: 
Sodium hypochlorite  solutions for water 
treatment  
  DRS 127 -1: 2018  
©RSB 2018 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2018  
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 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rs b.gov.rw   
ePortal: www.portal.rsb.gov.rw   DRS 127 -1: 2018  
iii                ©RSB 2018 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Application  ................................ ................................ ................................ ................................ .... 1 
3 Description  ................................ ................................ ................................ ................................ .... 1 
3.1 Identification  ................................ ................................ ................................ ................................ . 1 
3.2 Commercial form  ................................ ................................ ................................ ..........................  1 
3.3 Physical properties  ................................ ................................ ................................ ......................  2 
4 Normative references  ................................ ................................ ................................ ...................  2 
5 Requirements  ................................ ................................ ................................ ................................  2 
6 Packaging and labelling ................................ ................................ ................................ ...............  2 
6.1 Packaging  ................................ ................................ ................................ ................................ ...... 2 
6.2 Labelling  ................................ ................................ ................................ ................................ ........  3 
Annex  A (normative)  Testing for insoluble matter in sodium hypochlorite solution  ........................  4 
A.1 Procedure  ................................ ................................ ................................ ................................ ...... 4 
A.2 Calculation  ................................ ................................ ................................ ................................ .... 4 
Annex  B (normative)  Determination of available chlorine  ................................ ................................ ... 5 
B.1 Principle of test methods  ................................ ................................ ................................ ............  5 
B.2 Reagents  ................................ ................................ ................................ ................................ ....... 5 
B.3 Procedure  ................................ ................................ ................................ ................................ ...... 5 
B.4 Calculation  ................................ ................................ ................................ ................................ .... 6 
Annex  C (normative)  Determination of free alkali  ................................ ................................ .................  7 
C.1 Principle of test method ................................ ................................ ................................ ...............  7 
C.2 Reagents  ................................ ................................ ................................ ................................ ....... 7 
C.3 Procedure  ................................ ................................ ................................ ................................ ...... 7 
C.4 Calculation  ................................ ................................ ................................ ................................ .... 7 
Annex  D (norma tive)  Determination of heavy metals (as Fe)  ................................ ..............................  9 
D.1 Apparatus  ................................ ................................ ................................ ................................ ...... 9 
D.2 Reagents  ................................ ................................ ................................ ................................ ....... 9 
D.3 Procedure  ................................ ................................ ................................ ................................ ...... 9 
Annex  E (normati ve)  Measurement of pH value  ................................ ................................ ..................  10 
Annex  F (normative)  Determination of sodium chlorite  ................................ ................................ ..... 11 
F.1 Principle of method  ................................ ................................ ................................ ....................  11 
F.2 Apparatus  ................................ ................................ ................................ ................................ .... 11 
F.3 Reagents  ................................ ................................ ................................ ................................ ..... 11 
F.4 Calculate  ................................ ................................ ................................ ................................ ...... 12 
F.5 Principle of method  ................................ ................................ ................................ ....................  12 
 DRS 127 -1: 2018  
©RSB 2018 - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with  Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 127-1 was prepared by Technical Committee RSB/TC 013, Water and sanitation . 
This second  edition cancels and replaces the first  edition (RS  127-1: 2011), which has  been technically revised.  
DRS 127 consists of the following parts, under the general title Bleaching agents  — Specification : 
 Part 1: Sodium hypochlorite solutions for water treatment  
 Part 2: Sodium hypochlorite solutions for industrial and domestic use   
Committee membership  
The following organizations were represented on the Technical Committee on Water and sanitation (RSB/TC 
013) in the preparation of this standard.  
Integrated Polytechnic Regional Centre/Kigali ( IPRC -Kigali ) 
Rwanda Utility Regulatory Authority (RU RA) 
TAI Consult Ltd  
University of Rwanda/College of Sciences and Technology ( UR/CST ) 
Water and Sanitation Corporation Ltd (WASAC) Rwanda  Standards Board  (RSB) – Secretariat  
  DRS 127-1: 2018  
1                ©RSB 2018 - All rights reserved  
 Bleaching agents — Specification — Part 1: Sodium hypochlorite  
solutions for water treatment    
1 Scope  
This Draft Rwanda Standard specifies the requirements and methods of test for sodium hypochlorite solutions 
used to produce potable water.  
2 Application  
This standard applies only to sodium hypochlorite solutions used to produce potable water. It does not apply to 
sodium hypochlorite solutions used for general disinfecting and bleaching.  
3 Description  
3.1 Identification  
3.1.1  Chemical name  
Sodium hypochlorite.  
3.1.2  Synonym or common names  
Liquid bleach, soda bleach, bleach lye.  
3.1.3  Relative molecular mass  
74,44.  
3.1.4  Empirical formula  
NaClO.  
3.1.5  Chemical formula  
NaClO . 
3.2 Commercial form  
The product is supplied as an aqueous solution with an available (active) chlorine concentration up to a mass  
fraction of 18 %.   
©RSB 2018 - All rights reserved                  2 
 3.3 Physical properties  
3.3.1  Appearance and odour  
Sodium hypochlorite solution (NaClO) is a clear light -yellow liquid  with a faint chlorinous odour.  
3.3.2  Density  
The density of the product varies between 1,13 g/ml and 1,30 g/ml at 20 °C  
4 Normative references  
There are no normative references in this  document . 
5 Requirements  
4.1 Sodium hypochlorite solution shall be a clear liqui d containing not more than 0.15 % insoluble matter, by 
weight.  
4.2 Sodium hypochlorite solution shall be miscible in water in all proportions.  
4.3 Sodium hypochlorite solution shall also, in addition to 4.1, comply with the requirements specified in Tabl e 
1, when tested in accordance with the tests specified therein . 
Table 1 — Requirements  for sodium hypochlorite solutions  
S/N Characteristic  Requirement  Method of test  
(i) Insoluble matter, % by mass, max  0.15  Annex A   
(ii) Available chlorine, % m/v, min.   10  Annex B   
(iii) Total free alkali (as NaOH), % m/v, max.  1.5  Annex C   
(iv) Iron (as Fe),  ppm, max.  0.4  Annex D  
(v) pH, min.   9  Annex E  
6 Packaging and labelling  
6.1 Packaging  
The sodium hypochlorite solutions shall be packaged in suitable containers made of polyethylene or stainless 
steel which shall be properly sealed, appropriately vented and able to withstand normal usage and 
transportation.  DRS 127-1: 2018  
3                ©RSB 2018 - All rights reserved  
 6.2 Labelling  
The containers shall b e labelled legibly and indelibly with the following information:  
a) chemical name of the product indicating its intended use;  
b) name and address of manufacturer and/or trademark;  
c) instructions for use and safety precautions;  
d) batch or code number of the solut ion  
e) net volume of the solution;  
f) per cent mass by volume of available chlorine;  
g) storage conditions;  
h) manufacture and expiry date; and  
i) country of origin  
  
©RSB 2018 - All rights reserved                  4 
 Annex  A 
(normative)  
 
Testing for insoluble matter in sodium hypochlorite solution  
A.1 Procedure  
Pour approximately 100 mL of the sodium hypochlorite solution into a tared 400 mL beaker, place on a 
laboratory platform balance and weigh to the nearest 0.1 g. Add 100 mL of distilled water and mix thoroughly. 
Filter through a tared gooch crucible. Wash the be aker and crucible with distilled water. Dry the crucible to a 
constant weight from 100 °C to 105 °C. 
A.2 Calculation  
Per cent  insoluble  matter =𝑀𝑎𝑠𝑠𝑜𝑓𝑟𝑒𝑠𝑖𝑑𝑢𝑒
𝑀𝑎𝑠𝑠𝑜𝑓𝑠𝑎𝑚𝑝𝑙𝑒 ×100 
  DRS 127-1: 2018  
5                ©RSB 2018 - All rights reserved  
 Annex  B 
(normative)  
 
Determination of available chlorine  
 
 
B.1 Principle  of test methods  
The sample is added to an acidified solution of potassium iodine and the released iodine titrated with standard 
sodium thiosulphate solution to the starch end point.  
B.2 Reagents  
B.2.1  Glacial acetic acid  
B.2.2  Standard potassium iodate solution — 0.1 N  
B.2.3  Starch indicator solution  — 0.5. Mix 0.5 % of solution starch with 5 mL of cold water and 
add 95 mL of boiling water. Mix, cool and store in a glass bottle. Replace frequently or add 0.1 % 
m/v salicylic acid to the starch solution to minimize deterioration . 
B.2.4  Potassium iodine crystals — Iodate Free.  
B.2.5  Standard Sodium Thiosulphate Solution — 0.1 N.  
Dissolve 25 g of sodium thiosulphate (Na2S2O3.5H2O) crystals in freshly boiled and cooled water, and dilute 
to 1 000 mL.  
NOTE  The solution is more stable if the glassware is cleaned with sulphuric or chromic acids and thoroughly rinsed 
with water before use.  
B.3 Procedure  
Dissolve 2 g to 3 g of potassium iodide crystals in 50 mL of water in a 250 mL conical flask.  
Add 10 mL of gla cial acetic acid, then pipette out a 3 mL aliquot of sample into the solution, keeping the tip of 
the pipette beneath the surface of the solution until drained.  
Titrate at once with 0.1 N standard sodium thiosulphate solution until the iodine colour is ne arly gone then add 
1 mL of starch indicator solution and complete the titration to the disappearance of the blue colour.   
©RSB 2018 - All rights reserved                  6 
 B.4 Calculation  
Available  chlorine  (as Cl)percent  mass  by volume =0.03546  ×100  ×AN
𝑉 
where,  
A = Volume in mL of standard sodium thiosulphate s olution required for titration of the sample,  
N = Normality of the standard sodium thiosulphate solution, and  
V = Volume in mL of original sample in aliquot used.  
 
 
 
 
 
 
 
 
 DRS 127-1: 2018  
7                ©RSB 2018 - All rights reserved  
 Annex  C 
(normative)  
 
Determination of free alkali  
C.1 Principle of test method  
The sample solution is added to a neutralized, mixed solution of barium chloride and hydrogen peroxide, which 
precipitates any carbonate and reduces the hypochlorite to chloride. The free alkali is then titrated with standard 
hydrochloric acid using phenolphth alein indicator.  
C.2 Reagents  
C.2.1 Barium chloride solution  — 100 g/L. Dissolve 100 g of barium chloride (BaCl2.2H2O) in water and dilute 
to one litre. Filter if turbid.  
C.2.2  Hydrochloric acid, standard  — 0.1 N.  
C.2.3  Hydrogen peroxide solution  — 3 %.  
C.2.4 Phonolphthalein indicator solution  — 0.5 %. Dissolve 0.5 g of phenolphthalein in 60 mL of 95 % ethyl 
alcohol and dilute to 100 mL with water.  
C.2.5  Sodium hydroxide solution  — 4 g/L.  
C.3 Procedure  
Place 50 mL of barium chloride solution and 30 mL of  hydrogen peroxide solution in a 250 mL conical flask, add 
10 drops of phenolphthalein indicator solution, and neutrolize with Na0H solution. Introduce into this neutral 
mixture 10 mL of the sample solution, shake or stir vigorously for one minute, and tit rate the sodium hydroxide 
solution with 0.1 N HCl until the pink colour disappears.  
C.4 Calculation  
Free  alkali  (as NaOH )g/L=𝑉1×N ×40
𝑉 
 
where,  
V1= Volume, in mL of standard HCL required,  
N = Normality of the hydrochloric acid, and   
©RSB 2018 - All rights reserved                  8 
 V = Volume, in mL of sample solution  DRS 127-1: 2018  
9                ©RSB 2018 - All rights reserved  
 Annex  D 
(normative)  
 
Determination of heavy  metals (as Fe)  
D.1 Apparatus  
C.1.1   Nessler Cylinders — 50 mL capacity.  
D.2 Reagents  
D.2.1  Ammonium per Sulphate  
D.2.2 Butanoic potassium thiocyanate solution  — Dissolve 10 g of potassium thiocynate in 10 mL  of water. 
Add suffiecient n -butonal to make up to 100 mL and shake vigorously till the solution is clear.  
D.2.3  Standard iron solution A — Dissolve 0.7202 g of ferrous ammonium sulphate in 100 mL of water, and 
5 mL of 1.5 (v/v) sulphuric acid and run in cautiously a dilute solution of potassium permangenate (0.2 % m/v) 
until a slight pink coloration remains after stirring well. Dilute with water to 1 000 mL and mix thoroughly. One 
millilitre of this solution contains 0.1 mg of iron as Fe.  
D.2.4  Standard iron solution B  — Taken 100 mL of standard iron solution A and dilute to 1 000 mL with 
water. One millilitre of this solution contains 0.01 mg of iron as Fe. This dilute solution shall be prepared fresh.  
D.3 Procedure  
D.3.1  Weigh 50.0 g of the sodium hypochlorite solution and evaporate it to dryness. Dilute it to 30 mL in a 
Nessler cylinder, add about 30 mg of ammonium persulphate and 15 mL of butanoic potassium thiocyanate 
solution. Make up to 50 mL, shake vigorously for abo ut 30 seconds and allow the layers to separate. Carry out 
a control test in another Nessler cylinder using 2 mL of standard iron and solution B. Compare the intensity of 
the colour produced in the butanol layers in the two cylinders.  
D.3.2  The limit presc ribed in Table 1 shall be taken as not having been exceeded if the intensity of colour 
produced with the sample is not greater than that produced in the control test.  
  
©RSB 2018 - All rights reserved                  10 
 Annex  E 
(normative)  
 
Measurement of pH value  
E.1 Measure the pH, at room temperature, using a pH meter equipped with a glass electrode capable of 
measuring pH values to an accuracy of 0.1 or better.  
A= Reaction vessel  
B= 250 mL separating funnel  
C= Test tube  
D= Rubber tube  
E= Rubber stoppers  
   
 Figure 1 — Apparatus for determination of sodium chl orate  
 
DRS 127-1: 2018  
11                ©RSB 2018 - All rights reserved  
 Annex  F 
(normative)  
 
Determination of sodium chlorite  
F.1 Principle of method  
Sodium chlorate is reduced by sodium bromide in 8 N hydrochloric acid. After dilution and addition of potassium 
iodide, the released iodine (equivalent to hypochlorite plus chlorate)  is titrated with standard sodium thiosulphate 
solution and starch indicator.  
F.2 Apparatus  
The apparatus ( see Figure 1) consists of a 1 000 mL of wide mouth reaction bottle (A), fitted with a double hole 
rubber stopper carrying a separating funnel B, conven iently graduated or marked at 10, 20 and 100 mL levels, 
and a delivery tube leading to a 50 mL test tube gas trap C. The test tube trap is fitted with rubber tubing and a 
glass mouthpiece, D.  
F.3 Reagents  
F.3.1  Concentrated hydrochloric acid.  
F.3.2  Sodium  bromide solution — 10 % w/v.  
F.3.3  Potassium iodine solution — 10 w/v.  
F.3.4  Standard sodium thiosulphate solution — 0.05 N.  
F.3.5  Starch indicator solution — 0.5 % m/v.  
F.3.6  Sodium bicarbonate.  
F.3.7  Procedure  
Pipettee out a 3 mL aliquot of the sample into the reaction bottle (A), add one millilitre of concentrated 
hydrochloric acid and 0.3 g of pure sodium bicarbonate to expel all the air from the vessel through the long test 
tube C, containing a saturated solu tion of sodium bicarbonate. Then add 20 mL of sodium bromide solution 
followed by 80 mL of concentrated HCL.  
Stopper the bottle and shake well. Allow to stand for 10 minutes. Add 20 mL of 10 % m/v potassium iodide 
solution through the separating funnel ca refully and titrate the liberated iodide against 0.05 N sodium thiosulphte 
solution using a few drops of a starch indictor solution. Turn a blank with all the reagents except the sample by 
proceeding in the same manner as that of the test.   
©RSB 2018 - All rights reserved                  12 
 F.4 Calculate  
Sodiu m chlorate  (as NaClO )g
Lx=(𝑉2−𝑉1) ×N ×17.75
𝑉 
where,  
V2= Volume in mL of sodium thiosulphate used for the test;  
V1= Volume in mL of sodium thiosulphate used for the blank;  
N = Normality of sodium thiosulphate solution;  
V = Voume in mL of sample solution used  
F.5 Principle of method  
Sodium chlorate is reduced by sodium bromide in 8 N hydrochloric acid. After dilution and addition of 
potassium iodide, the released iodine (equivalent to hypochlorite plus chlorate) is titrated w ith standard 
sodium thiosulphate solution and starch indicator.  
 DRS 127-1: 2018  
ICS 71.100.80  
 
 
©RSB 2018 - All right s reserved