In this experiment I have provided the complete information regarding limit test for sulphate and also preparation of 0.1 N sulphuric acid and barium sulphate reagent for your better understanding.

1. EXPERIMENT NO:2
LIMIT TEST FOR SULPHATES
Prepared by
Dr Anumalagundam Srikanth
Dept. of Pharmaceutical Analysis

2. LIMIT TEST
Theory :
limit test are the quantitative and semi quantitative test designed to
identify and control small quantity of impurities which are likely to be present
in the drugs or pharmaceutical substance.
(or)
Limit test are used for identify and control small quantity of impurities in
drugs.

3. Aim:
To carry out the limit test for Sulphates.
Apparatus :
Nessler’s cylinders 50 ml 2 nos., beakers, glass rod etc…,
Materials:
 Sodium chloride (NaCl) (sample which does not contains chlorides)
Sulphuric acid (H2SO4)
Hydrochloric acid (HCl)
Barium chloride (BaCl2)
Potassium sulphate (K2SO4 )
Alcohol

4. Solutions :
 Sulphuric acid ( 0.1 M) :
5.4 ml of sulphuric acid and dilute up to 1000 ml with distilled water.
Assay of H2SO4 normally available was 96 % - 98 % ( 98 ml in 100 ml / likely 980 ml in 1000 ml )
Density of HCl was 1.8
Density = mass/ volume
Mass= density X volume
Mass= 1.8 X 980 = 1764 gm
No. of moles present in H2SO4
No.of moles present in sample = weight of sample / molecular weight
For H2SO4 = 1764 ( weight of H2SO4) / 98 (M.W)
= 18 N of H2SO4

5. We need to prepare 0.1 N by using the formula
N1 V1 = N2 V2
Where
N1 = 18 , V1 = ? , N2 = 0.1 , V2 =1000
18 X v1 = 0.1 X 1000
V1 = 0.1 X 1000/18
= 5.4 ml

6. Barium sulphate reagent (BaSO4):
Mix 15 ml of 0.5% barium chloride (BaCl2)with 55 ml of water and 20ml of
sulphate free alcohol and 5 ml of 0.0181 % of Potassium sulphate (K2SO4 ).
Dilute to 100 ml with distilled water. Always use freshly prepared Barium
sulphate reagent (BaSO4).

7. PRINCIPLE :
The limit test for Sulphate is mainly used to control sulphate impurities in inorganic
substances. If depends upon the precipitation of the sulphate with Barium sulphate reagent
(BaSO4) in the presence of HCl. The turbidity so obtained is compared with standard turbidity
contain a known amount of sulphate ion.
The reaction involved is as follows.
H2SO4 + BaCl2 BaSO4 + 2HCl

8. PROCEDURE:
Sample :
 Dissolve the specified quantity of the NaCl in 10 ml of distilled water and transfer
to a Nessler cylinder or glass.
 Add 2 ml of dil.HCl.
 Dilute to 45 ml with distilled water.
 Add 5 ml of BaSO4 reagent.
 Stirr immediately with a glass rod, and set a side for 5 min the turbidity
produced is not greater than the standard turbidity.

9. Standard :
 Take 2.5 ml of 0.1 H2SO4 and transfer to a Nessler cylinder.
 Add 10 ml of dil.HCl.
Dilute to 45 ml with distilled water.
Add 5 ml of BaSO4 reagent.
 Stirr immediately with a glass rod, and set a side for 5 min.

10. Observation :
Standard shows more turbidity than sample.
Report :
The given sample was passes limit test of sulphates.
References:
1. Practical pharmaceutical inorganic chemistry by Dr.G.Devala Rao., Birla
publications Pvt.Ltd., New Delhi. Page no: 38.
2. IP 1985