CDC 7  (207) CD 2 
 
 
 
 
 
© TBS 2020                  First Edition 2020  
 DRAFT TANZANIA STANDARD  
 
 
 
 
 
 
 
 
Sodium carbonate (Soda ash)  – Specification  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TANZANIA BUREAU OF STANDARDS  
 
 
 
 CDC 7 (207)  CD 2 
 
2 
  
Introduction  
Sodium carbonate , anhydrous (Na 2CO 3) is commonly named as s oda ash . It is a white, finely 
crystalline, water soluble material produced in several commercial forms, which differ only in 
their physical characteristics, that is, with respect to size, shape of particles, and bulk density. 
The standard forms are light, medium a nd dense soda ash, graded according to the bulk 
density. Dense soda ash is further classified with reference to particle size and is generally 
used for glass, silicate and chromate industries.  
Soda ash is one of the most important industrial chemicals and  the most widely used fixed 
alkali for the manufacture of other alkali products, sodium salts, glass, soap, pulp and paper, 
iron and steel, cellulose and rayon, cleaning compounds, water softening chemicals, textiles, 
drugs, etc. There are few industries, indeed which do not consume soda ash in their own 
operations or do not employ materials which were made partly with soda ash.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 7 (207)  CD 2 
 
©TBS 2020 – All rights reserved                                                                                              3  
Foreword  
 
This Draft Tanzania Standard is being developed by the Industrial and Laboratory Chemicals 
Technical Committee under supervision of the Chemical Division Standards Committee and it 
is in accordance with the procedures of the Bureau.  
 
In the preparation of this Tanzania Standard assistance has been drawn from:  
 
IS 251:1998  (Reaffirmed 201 9) Soda ash, technical - Speci fication , published  by the 
Bureau of Indian Standards  
 
Acknowledgement is hereby made for the assistance derived from this source.  
 
In reporting the result of a test or analysis made in accordance with this Tanzania Standard, if 
the final value, observed or calculated is to be rounded off, it shall be done in accordance with 
TZS 4 rounding  off numerical values.   CDC 7  (207) DTZS  
 
 
©TBS 2020 – All rights reserved                                                                                                   
                                                                                                                                           
 DRAFT TANZANIA STANDARD                                                                        CDC 7 (207) DTZS  
 
 
Sodium carbonate (Soda ash)  – Specification  
 
 
1 Scope  
 
This Draft Tanzania S tandard prescribes the requirements, sampling and test methods for  sodium 
carbonate  (soda ash).  This standard does not cover Sodium Carbonate for food application.  
 
2 Normative references  
 
The following referenced documents are indispensable for the application of this document. The 
latest edition of the referenced docume nt (including any amendments) applies;  
 
TZS 59 Water for analytical laboratory use – Specification and test method  
TZS 505  Specification for hydrochloric acid  
 
3. Terms and definitions  
 
<<<<<Not applicable>>>>>  
 
4. Requirements  
 
4.1 General requirements  
 
4.1.1 Grades  
 
The material shall be of three grades, namely, dense, medium and light depending upon the bulk 
density  described in 4.1.2 below;  all having the same chemical composition as given in Table 1.  
 
4.1.2 Bulk Density  
 
When determined as prescribed  in Annex A the bulk density of the material shall be as given below:  
 
a) Dense Grade - 951 to 1 250 kg/ m3  
b) Medium Grade - 751 to 950 kg/m3  
c) Light Grade 500 to 750 kg/m3  
 
4.1.3 Appearance  
The material shall be a white, uniform texture d, free from dirt and other foreign matter.  
 
4.2 Specific requirements  
The material, when tested according to the methods prescribed in Annex C, shall comply with the  
specific  requirements given in Table 1.  
 
 
 
 
 
 
 
 
 CDC 7 (207) DTZS  
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Table 1 Specific requirements for Sodium carbonate  (Soda ash).  
 
S/N Characteristic  Requirement (on dry basis)  Method of test  
1.  Total alkalinity (as Na 2CO 3), 
percent by mass, Min  98.5 C-3 
2.  Matter insoluble in water. percent 
by mass, Max  0.15 C-4 
3.  Volatile matter content, percent 
by mass, Max  2 Annex B  
4.  Sulphate (Na 2SO4), percent by 
mass, Max  0.081 C-5 
5.  Chloride (as NaCl), percent by 
mass, Max  1.02 C-6 
6.  Iron (as Fe 2O3) percent by mass, 
Max 0.007  C-7 
 
1when produced by the modified Solvay process, the sulphate content shall be 0.5 percent, Max. 
2For sodium dichromate industry, chlorides (as NaCl), percent by mass. Max, shall be 0.4.  
 
5 Packing and Marking  
5.1 Packing  
The material shall be supplied in clean, dry and tight containers, without faults , made of material 
which do not  affect the contents.  
5.2 Marking  
Each package shall be securely closed and marked with the following information  in English and/or 
Kiswahili :  
a) Name of material  and grade  
b) Manufacturer's name  and address  
c) Recognized trade -mark, if any  
d) Country of origin  
e) Net content   
f) Lot or batch number  
g) Manufacturing date  
 
6 Sampling   
 
Representative samples of the material shall be drawn as prescribed in Annex D.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 7 (207) DTZS  
©TBS 2020 – All rights reserved                                                                                              3 
Annex A   
(Normative ) 
 Determination of Bulk Density  
 
 
A-1 Apparatus    
A-1.1 Assemble the apparatus as shown in Fig. 1. The base of the measuring cylinder A shall be 
ground flat and the empty measuring cylinder together with the rubber bung shall weigh 250 ± 5 g. It 
shall be accurately calibrated to 250  mL with an error, if any, of less than 1 mL. The distance 
between  zero and 250  mL graduation mark on the measuring cylinder A shall not be less than 220 
mm and not more than 240 mm.  The distance between the flat -ground part of the base of measuring 
cylinder A and the rubber base pad B, when the measuring cylinder A is raised to the full height, shall 
be 50 ± 2 mm.  
A-1.1.1 Rubber Base Pad  
 
The rubber base pad B shall have a share hardness of 42 to 50.  
A-1.1.2 Funnel  
Made of glass, with an angle of 60°C . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
All dimensions in millimeters.  
Fig. 1 APPARATUS FOR 
DETERMINATION OF BULK 
DENSITY  
A-2 Procedure  
 
Take a sufficient quantity of the material on a glazed paper and slip it gently and smoothly through 
the funnel into the measuring cylinder A up to 100  mL mark without knocking. With the thumb and 
fingers of one hand, gently grasp the upper portion of the cylinder and lift it as far as 50 mm height. 
Release the cylinder on the table. Repeat this knocking a second time. Again, slip more of the 
material into the cylinder gently and smoothly as before up to 200  mL mark and give two knocks as 
before by lifting the cylinder to 50  mm height. Finally, slip more of the material into the  cylinder as 
before up to 250  mL mark and give two further knocks of 50 mm hei ght. Level the cylinder with the 
material without any further knocking. Empty out the material from the cylinder and weigh the 
material to the nearest 0.1 g.  
 
A-3 Calculation  
 
Bulk density, kg/m3 = 4 M  
 
where  
M = massing of the material in the cylinder  
 CDC 7 (207) DTZS  
4 
  
Annex B  
(Normative)  
 Determination of volatile matter content  
 
 
B.1 Apparatus   
 
B.A.1 weighing  scale  
B.A.2 weighing bottle with glass stopper  
B.A.3 Heater (capacity of 350 °C) 
 
B-2 Procedure  
Place about 2 g of the material in a weighing bottle provided with a glass stopper and weigh 
accurately. Remove the stopper and heat for about one hour at a temperature of 250 °C to 300°C. 
Cool in a desiccator, and replace the stopper and weigh. Repeat unti l mass remains constant.  
 
B-2 Calculation  
 
Volatile matter content, percent by mass = 100  (𝑀1− 𝑀2)
𝑀1 
 
where  
𝑀1= mass  in g of the material before heating, and  
𝑀2= mass in g of the material after heating.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 7 (207) DTZS  
©TBS 2020 – All rights reserved                                                                                              5  
Annex C   
(Normative)  
Methods of test for sod ium carbonate (sod a ash ) 
 
 
C-1 Quality of reagents  
Unless specified otherwise, water for analytical laboratory use (see clause 2) shall be used in  tests.  
 
C-2 Preparation of the material  
Dry about 25 g of the material as prescribed in Annex B and keep in a desiccator. Use this prepared 
sample for analysis.  
  
C-3 Determination of total alkalinity  
C-3.1 Reagents  
C-3.1.1 Standard Sul furic Acid  – 1N 
C-3.1.2 Methyl Orange Indicator Solution  
Dissolve 0.0 1 g of methyl orange in 100 m L of water.  
 
C-3.2 Procedure  
Weigh about 1 g of the prepared sample (see C-2). Transfer it completely to a 500  mL conical flask 
and dissolve it in a 100 m L of water. Add 4 drops of methyl orange indicator solution and titrate with 
standard sul furic acid. The colour changes from yellow to pale red orange at the end point.  
  
C-3.3 Calculation  
Total alkalinity (as Na 2CO3), percent by mass  = 5.3 𝐴 𝑁
𝑀  
Where,  
A = volume in m L of standard sulfuric acid used in the titration,  
N = normality of standard sulfuric acid, and  
M = mass  in g of the prepared sample (see C-2) taken for the test.  
 
C-4 Determination of matter insoluble in water  
C-4.1 Procedure  
Weigh about 10 g of the prepared sample (see C-2). Transfer it to a 400  mL beaker, add about 200 
mL of freshly boiled distilled water and boil the solution for about 10 min. Filter through a  weighed 
sintered glass crucible (G No. 4) . Wash thoroughly with hot water and dry to constant mass at 110 ± 
2°C. 
  
C-4.2 Calculation  
Matter insoluble in water, percent by mass= 100  𝑀1
𝑀2  
 
where  
𝑀1 = mass in g of the residue, and  
𝑀2 = mass in g of the prepared sample taken for the test.  
 
 
  CDC 7 (207) DTZS  
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C-5 Determination of sulphates  
 
C-5.1 Reagents  
C-5.1.1 Concentrated hydrochloric acid (See TZS 505 )  
C-5.1.2 Barium chloride solution - 10 percent.  
 
C-5.2 Procedure   
Dissolve about 10 g of the prepared sample (see C-2), in 100 m L of water and add hydrochloric acid 
to make the solution slightly acidic. Boil to decompose the carbonates. Cool  the contents,  filter 
through a folded filter paper and wash the filter paper thoroughly, collect the filtrate and washings in a 
500 mL beaker.  Dilute the combined filtrate and washings to about 250 m L, boil and add 10 mL of hot 
barium chloride solution to the boiling solution. Boil again for 2 min, let it stand for 4 h rs and filter 
through a tared sintered  crucible. Wash the precipitate and dry to constant mass at 105 ± 2°C.  
 
C-5.3 Calculation  
Sulphates (as Na 2SO 4), percent by mass = 60.86 𝐶
𝑀  
 
where  
C = mass in g of the precipitate, and  
M = massing of  the prepared sample (see C-2) taken  for the test.  
 
 
C-6 Determination of chlorides  
 
C-6.1 Reagents  
C-6.1.1 Concentrated Nitric Acid,  
C-6.1.2 Standard Silver Nitrate Solution, 0.1 N.   
C-6.1.3 Nitrobenzene  
C-6.1.4 Standard Ammonium Thiocyanate Solution, 0.1 N.  
C-6.1.5 Ferric Alum Indicator, saturated solution.  
 
C-6.2 Procedure  
Transfer about 2 g of the prepared sample (see C-2) to a conical flask, neutralize with nitric acid and 
then add 5 m L of the acid in excess. Add 20 m L of standard silver nitrate solution  followed by  3 mL of 
nitrobenzene and shake vigorously. Titrate with s tandard ammonium thiocyanate solution using ferric 
alum indicator, until the colour of indicator changes from colourless to faint distinct reddish brown 
colour.  
 
C-6.3 Calculation  
Chlorides (as NaCl ) percent by mass = 5.845  (20 𝑁1−𝑉 𝑁2
𝑀  
 
Where,  
  
𝑁1= normality of standard silver nitrate solution,  
𝑉 = volume in ml of standard ammonium thiocyanate solution used in C-6.2,  
𝑁2= normality of standard ammonium thiocyanate solution, and  
𝑀 = mass in g of the prepared sample (see C-2) taken for the test.  
 
 
 
 
C-7 Determination of Iron  CDC 7 (207) DTZS  
©TBS 2020 – All rights reserved                                                                                              7  
C.7.1 Method A.   
C-7.1.1 Apparatus  
Nessler cylinders, 100 mL capacity  
 
C-7.1.2 Reagents  
C-7.1.2.1 Dilute hydrochloric acid, approximately 15 percent (m/v), free from iron.  
C-7.1.2.2 Ammonium persulfate  
C-7.1.2.3 Potassium thiocyanate solution, 5 percent.  
C-7.1.2.4 Dilute sulfuric acid, 10 percent (m/v).  
C-7.1.2.5 Standard iron solution - Dissolve 0.490 g of ferrous ammonium sulphate                   
[FeSO 4.(NH 4)2 SO 4.6H 2O] in 10 mL of dilute sulfuric acid and dilute with water to 1 000 mL. 1  mL of 
the dilute solution is equivalent to 0.1 mg of iron (as Fe 2O3).  
 
C-7.1.3 Procedure   
Weigh accurately 1.00 g of the prepared sample (see C-2) and dissolve it in about 20 mL of water. 
Add about 5 mL  of hydrochloric acid to make it acidic and 30 mg of ammonium persulfate and boil to 
oxidize the iron. Cool and transfer the contents to a Nessler cylinder, add 5 mL of potassium 
thiocyanate solution, dilute to the mark with water, and stir thoroughly. Int o a second Nessler 
cylinder, add 5 ml of hydrochloric acid, about 30 mg of ammonium persulfate, 5 mL of potassium 
thiocyanate solution and 0. 7 mL  of standard iron solution. Dilute to the mark with water. Compare the 
colour of the solution in the two cylinders.  
C-7.1.4 Conformity criteria  
The limit prescribed in Table 1 shall be taken as not having been exceeded if the intensity of colour 
produced with the prepared sample (see C-2) is not greater than that produced by the standard iron 
solution.  
 
Alternative Method  
C.7.2 Method B   
C.7.2.1  Reagents:  
C.7.2.1.1  Conc. Hydrochloric acid  
C.7.2.1.2  Sodium hydroxide solution  1 M 
C.7.2.1.3  Citric acid  20% w/v  
C.7.2.1.3  Thioglycolic acid (mercaptoacetic acid)  
C.7.2.1.3  Ammonia  10 M 
C.7.2.1.3  Iron standard solution , 0.7 ppm  
 
C.7.2.1.3  Procedure  
i) Solution S: Dissolve 1 g of sodium carbonate in portions in a mixture of 5 mL Hydrochloric acid and 
25 mL d istilled water. Heat the solution to boiling, then cool. Add dilute sodium hydroxide solution 
until the solution is neutral and dilute to 50 mL with distilled water  
ii) Dilute 5 mL of solution S to 10 mL with water in a Nessler  cylinder. Add 2  mL of 20% w/v solution 
ofcitric acid and 0.1 mL of thioglycolic acid, mix, then make alkaline with 10  M ammonia, dilute to 20 
mL with water and allow to stand for 5 min. Treat 10 mL of iron standard solution (0.7 ppm) in the 
same manner a s sample. The sample is considered to not having more than 0.007% m/m if the pink CDC 7 (207) DTZS  
8 
 colour produced is not more intense than that produced by the standard solution.  
Alternatively: To quantify the exact amount of Iron, solution S can be subjected to any eleme ntal 
analyzer  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 7 (207) DTZS  
©TBS 2020 – All rights reserved                                                                                              9 Annex D  
(Normative)  
Sampling of Sodium carbonate (S oda ash ) 
 
 
D-1 General requirements of sampling  
D-1.0 While drawing samples  the following precautions and directions shall be observed.  
D-1.1 Samples shall not be taken in an exposed place.  
D-1.2 The sampling instrument shall be clean and dry.  
D-1.3 Precautions shall be taken to protect the samples, the material being sampled,  the sampling 
instrument and the containers for samples from the adventitious contamination.  
D-1.4 Samples shall be placed in suitable, clean, dry and air -tight glass containers,  
D-1.5 The sample containers shall be of such a size that they are almost co mpletely filled by the 
sample.  
D-1.6 Each sample container shall be sealed air -tight after filling and marked with full details of 
sampling, the date of sampling and the year of manufacture of the material.  
 
D-2 Scale of sampling  
 
D-2.1 Lot  
In any consignment of one grade of soda ash, all the containers of the same size and drawn from a 
single batch of manufacture shall constitute a lot. If a consignment of one grade of soda ash is known 
to consist of different batches of manufacture or of di fferent sizes of containers, then the containers 
belonging to the same batch and size shall be grouped together and each such group shall constitute 
a separate lot.  
D-2.2 For ascertaining the conformity of the lot to the requirements of the specification,  tests shall be 
carried out for each lot separately. The number of containers (n) to be selected for this purpose shall 
depend on the size of the lot (N) and shall be in accordance with Table 2.  
D-2.3 The container shall be selected at random from the lot and in order to ensure randomness of 
selection, the following procedure is recommended for use.  
 
Arrange all the containers in the lot in a systematic manner  and starting from any container, count 
them as 1, 2, 3,......, etc, up to r and so on, where r is the integral part of N/n. Every rth container thus 
counted shall be withdrawn to give sample for tests.  
 
Table 2 Scale of Sampling  
 
Lot size  No. of containers to be selected  
N n 
Up to 15  3 
16 to 40 4 
41 to 65  5 
66 to 110  7 
111 and above  10 
 
 
D-3 Preparation of test samples  
D-3.1 In taking out samples from a container of soda ash, care shall be taken to exclude portions 
where caking is noticeable (due to absorption of moisture and carbon dioxide). This may be done by 
removing from the top about 20 cm of the material in the containe r and then taking out the sample 
from the centre of the remaining portion. The total quantity of the material so collected from a CDC 7 (207) DTZS  
10 
 container shall be not less than 300 g. The material drawn from different containers shall be mixed 
together and by the proces s of coning and quartering an ultimate sample of about 750 g shall be 
obtained. This test sample shall be divided into three equal parts, one for the purchaser, another for 
the supplier and the third shall be used as a refere nce sample.  
D-3.2 AII the test  samples shall be transferred to separate containers and shall be sealed and 
labelled with full identification particulars. The referee test sample, bearing the seal of both the 
purchaser and the supplier, shall be kept at a place agreed to between the two  and shall be used in 
case of any dispute.  
 
D-4 Number of tests and criteria for conformity  
  
D-4.1 Tests for the determination of all the requirements given in 3 shall be performed on the test 
sample as obtained in D-3.1.  
D-4.2 The lot shall be declared as conforming to the requirements of this specification if all the test 
results as obtained under D-4.1 are found satisfactory.