Experiment No. 3 Modified limit test for Chlorides and Sulphates Limit test for Iron

Modified limit test for Chlorides and Sulphates Limit test for Iron

Experiment No. 3a

Aim: To carry out the Modified Chloride limit test of the given test substance. 

Requirements: (a) Glasswares: Nesslers’ cylinder, measuring cylinder and glass rod. 

 (b) Chemicals: Dil. Nitric acid, 0.1 M silver chloride, conc. HCl, distilled water. 

Principle: Limit test of chloride is based on the precipitation reaction. The precipitates of chlorides develop on reaction of soluble chloride with silver nitrate in the presence of dilute nitric acid to form silver chloride, which appears as solid particles (opalescence) in the solution. The intensity of turbidity depends on the amount of chlorides present in the test substance. 

Procedure: With reference to International Pharmacopoeia 6th Edition 2016, the limit test of chloride has been modified in the context of standard solution preparation. Earlier the standard solution of chloride was prepared by dissolving sodium chloride (NaCl, known Cl− impurity) but now it has been modified by using hydrochloric acid (HCl) instead of sodium chloride (NaCl). 

                                                             HCl + AgNO3 → AgCl + HNO3 

 Conclusion: If opalescence produced in sample solution is less than the standard solution, the sample will pass the limit test of chloride and vice versa.


Experiment No. 3b

Aim: To perform the Modified limit test for Sulphate of the given test sample. 

Requirements: (a) Glassware: Nesslers’ cylinder, measuring cylinder and glass rod. 

 (b) Chemicals: Potassium sulphate, test substance, hydrochloric acid, barium sulphate reagent and distilled water. 

Principle: The principle involved in the limit test for sulphates is precipitation method. The sulphates are precipitated as barium sulphate by reacting with barium chloride in the presence of hydrochloric acid. The hydrochloric acid used prevents the reaction of other acid radicals with barium chloride as in the presence of hydrochloric acid, only sulphates are precipitated. 



Due to the formation of precipitates, the solution appears turbid and the extent of turbidity depends on the amount of sulphates present. If the turbidity produced by the test is less than that of standard, it means that the sample contains sulphates within prescribed limits. 


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